System and method for a SKIM foiling electric-powered boat

Abstract

A system and method of skim foiling electric-powered boat apparatus. This electric recreational boat or watercraft will utilize "skim foiling," a simplified hydrofoil approach designed to make the benefits of hydrofoil technology. The apparatus consists of a main foil behind a center of gravity (CG) to create a nose-down moment and a left-side and right-side mounted transom elevons that are in contact with and submerged underwater. The apparatus is configured for low-speed skimming and high-speed skimming. As speed increases, the apparatus flattens along the surface of the water.

Description

SYSTEM AND METHOD FOR A SKIM FOILING ELECTRIC-POWERED BOAT APPARATUSCross Reference to Related Applications

[0001] This application claims the benefit of, and priority to U.S. Provisional Application No. 63 / 675,321 filed on July 25, 2024 and entitled “SYSTEM AND METHOD FOR A SKIM FOILING ELECTRIC- POWERED BOAT APPARATUS”, the entirety of which is incorporated by reference herein.Background

[0002] The embodiments described herein relate to watercraft, and more particularly to an electric powered boat equipped with a hydrofoil system that lifts the hull just above the water surface (“skim foiling”) to reduce drag while maintaining stability and simplicity.

[0003] Recreational motorboats traditionally use planing hulls that skim along the water at speed, supported by hydrodynamic lift from the hull’s underside. In recent years, hydrofoiling boats - which use wing-like foils below the hull to lift the entire hull out of the water - have demonstrated dramatic improvements in efficiency by reducing wetted surface area and drag. However, full hydrofoil designs come with challenges. They typically require complex mechanical systems (retractable foils, active control surfaces) and advanced control algorithms to maintain stable flight above the water. This complexity leads to high manufacturing and maintenance costs and can intimidate average boaters. The significant elevation (often several feet above water) also makes the ride different from a normal boat, potentially limiting mainstream appeal. On the other hand, conventional planing boats are simpler and familiar but inherently inefficient - a large portion of the hull remains in contact with water, causing high drag and fuel (or battery) consumption.

[0004] There exists a need for a solution that combines the efficiency gains of hydrofoils with the practicality and simplicity of planing hulls. Some attempts have been made in this direction, such as hydrofoil -assisted boats that use small foils to augment lift (e.g. “foil assist” kits on pontoon boats that lift the bow a few inches). While these reduce drag somewhat, they do not eliminate most of the hull -water contact and thus miss the full benefit.

[0005] Fully foiling electric boats (for example, the Candela C-8 or Navier N30) achieve drag reduction but at the cost of complex electronics, multiple foils, and high price points - essentially targeting a luxury market. The average boater would benefit from a simpler system that yields significant drag reduction(approaching that of true hydrofoils) but with simplified hardware and software. Additionally, stability in real-world conditions (choppy water, turns, varying loads) is a concern.

[0006] A traditional fully submerged foil boat can be less stable without active control, whereas a conventional boat naturally regains stability by contacting the water. An ideal solution would keep the hull very close to the water surface, allowing it to re-engage for stability when needed, while normally operating with the hull just out of the water to minimize drag. Keeping the hull close to the water is also a stability advantage when operating in choppy or wavy water. In summary, the disclosure addresses the need for a cost-effective, user-friendly hydrofoil system that provides substantial efficiency gains, maintains a familiar boating experience, and is easier to control and produce.

[0007] Traditional hydro-foiling boats, which elevate the hull far above the water to reduce drag, come with several challenges that limit their appeal and practicality for the broader recreational boating market. These challenges include high manufacturing costs due to complex mechanical and hydraulic systems, operational complexity that may deter average consumers and increase maintenance costs, and potential stability issues in choppy conditions. Furthermore, the significant elevation above water can make these boats look and feel unfamiliar and intimidating to traditional boaters, thus hindering broader market adoption. Additionally, the complexity and cost associated with traditional hydrofoil designs can make them less accessible to the average boater, creating a barrier to the adoption of cleaner, more efficient hydrofoil technologies.Summary

[0008] A system and method of skim foiling electric-powered boat apparatus. This electric recreational boat or watercraft will utilize "skim foiling," a simplified hydrofoil approach designed to make the benefits of hydrofoil technology more available to the broader public. The apparatus consists of a main foil behind a center of gravity (CG) to create a nose -down moment and left-side and right-side mounted transom elevons that are in contact with the water. Elevons are flaps / control surfaces that combine the function of elevator and ailerons and must remain submerged under the water to have control effect. The apparatus is configured for low-speed skimming and high-speed skimming. As speed increases, the apparatus flattens along the surface of the water.

[0009] The present disclosure provides a skim foiling boat system that lifts the hull only minimally out of the water - just enough to significantly cut drag - thereby blending efficiency with stability. In one aspect, the disclosure is a watercraft (e.g., an electric recreational boat) having: (a) a main hydrofoil mounted slightly aft of the craft’s center of gravity (CG), which generates lift to raise the hull and inherently producesa small nose-down pitching moment; (b) a pair of transom-mounted control flaps, one on each side at the stem, referred to as elevons (combined elevator and aileron surfaces). These elevons remain submerged in the water flow and serve to actively control the boat’s pitch and roll; and (c) a central steerable outboard motor assembly at the stem (which may be an electric outboard) that provides propulsion and also can be tilted (trimmed) to influence the craft’s pitch or lift. Other standard marine propulsion systems, such as stem drive may be used preferably if they are capable of tilt and directional steering. The system is configured to operate in two primary modes - a low-speed mode (hull supported by buoyancy / planing) and a high-speed skim-foiling mode where the hull is lifted preferably clear of the water. As the boat accelerates and transitions to the foiling mode, it automatically levels out (reducing pitch angle) so that it skims along the surface at a steady, low elevation.Brief Description of the Drawings

[0010] FIG. 1 is a diagram illustrating a right-side view of an exemplary watercraft.[Oi l] FIG. 2 is a diagram illustrating a back plan view of the watercraft.

[0012] FIGURES 3A and 3B are diagrams illustrating operation of the watercraft..

[0013] FIG. 4 is a control system block diagram of the exemplary watercraft.Detailed Description

[0014] In a typical hydrofoil -equipped watercraft, the hydrofoil (or “foil”) is rigidly mounted to the underside of the watercraft.. Traditional hydrofoil boats (e.g. modem electric foilers like the Candela C8 or Navier N30 ) fully lift the hull out of water for efficiency but require complex control systems and multiple foils. In contrast, conventional planing boats or bolt-on hydrofoil assist kits (e.g. Hydrofin pontoon foils or Doel-Fin outboard fins) only partially lift the boat hull from the water (i.e., counter only a fraction of the weight of the hull) or simply improve planing speed.

[0015] The herein-disclosed skim foiler finds a middle ground: it aims to lift the hull minimally out of the water (just skim the surface) to greatly reduce drag yet keep the boat very close to the water for passive stability and simpler control. The disclosed disclosure combines a main foil, placed slightly aft of the center of gravity (CG) to create a self-correcting nose-down moment, with a pair of small stem elevons for active pitch and roll control, all integrated with a conventional steerable outboard motor. Elevons are flaps / control surfaces that combine the function of elevator and ailerons and generally remain submerged under the waterto have the best control effect. One embodiment of the disclosure uses a single fixed main foil just behind the CG (creating inherent longitudinal stability) and two stem “elevon” flaps for control.

[0016] According to the disclosure, a watercraft is disclosed with a foil mounted to a moveable assembly (a motor / foil assembly, or MFA), which assembly is configured to retract by moving up towards the underside of the watercraft when extension of the foil is not required, and to deploy by moving downwards away from the underside of the watercraft when extension of the foil is required. The movement may be actuated by actuators or may be affected through forces created by the primary propulsion motor and control surfaces of the watercraft.

[0017] This disclosure introduces a skim foiling system designed primarily for recreational boats. It leverages a minimal hydrofoil elevation strategy, keeping the boat's hull at or just above the water surface, which simplifies the design and reduces the need for complex control mechanisms. The system comprises a central steerable motor with integrated tilt-lift functionality for propulsion and lift control, two lateral elevons at the aft for enhanced pitch and roll stability, and a fixed main foil with a straightforward linear retraction mechanism for depth adjustment. Alternate embodiments include a hinged swing-down deployment system or a 4-bar mechanism. This design markedly lowers the boat's mechanical complexity and manufacturing costs compared to traditional hydrofoiling systems, while still offering the core benefits of hydrofoiling such as reduced drag and increased efficiency. By maintaining close proximity to the water, the disclosure also addresses stability concerns in varied water conditions, making it more approachable and appealing to the general boating market. The use of a conventional outboard motor (i.e., electric or combustion outboard style motor) enhances the system's versatility, parts re-use and familiarity, further broadening its appeal.

[0018] A unique feature of the skim foiling system is its adaptability to conventional outboard motors, allowing for an easier integration into existing boat designs and manufacturing processes, including retrofit potential. This adaptability could be a distinctive marker in identifying the use of this technology in competitor products.

[0019] In alternate embodiments of the disclosure, a variable geometry foil system that can adjust its lift characteristics without impinging on the specific design of the skim foiling system may be considered. Detecting the use of this disclosure by competitors could involve monitoring for boats that advertise the combined benefits of hydrofoil efficiency and planing boat simplicity, particularly those that specify low- elevation hydro-foiling capabilities.Design Overview

[0020] According to the disclosure, elements of this design comprise the following:• Skim Foiling Technology: A streamlined hydrofoil design that maintains minimal height above water for efficiency, paired with a conventional outboard motor for propulsion• User-Friendly Mechanics: Featuring fewer actuators and simplified controls, the watercraft is designed for ease of use and maintenance, appealing to a wide range of boaters.• Optimized Stability and Performance: The watercraft will provide stable, efficient cruising, particularly on flat water, with quick acceleration and a comfortable ride, making it versatile for various recreational activities.Concept and Configuration

[0021] FIG. 1 is a diagram illustrating a right-side view of an exemplary watercraft configured for highspeed skimming. According to FIG. 1, the hull just above the water surface, with the main hydrofoil aft of the center of gravity and the stem elevon flaps at the waterline. The transom of the exemplary watercraft is in (or nearly in) contact with the water. The main foil is mounted behind (slightly aft of) the boat’s center of gravity (CG), to create nose-down moments which can be counteracted by the elevon flaps. This is important for longitudinal stability (similar to an aircraft with an aft tail producing downforce) and directional stability: placing the lifting foil (and its stmt) behind the CG means any lateral slippage will create a self-centering yaw moment, improving straight-line tracking.

[0022] According to FIG. 1, features of the exemplary watercraft include the following:• No ailerons or moving parts on the Main foil• Transom-mounted elevons are at minimal depth at each side• Pitch of boat controls lift on main foil• Center transom minimal depth outboard motor steers and propels• As speed increases, the boat flattens along the surface (to reduce the lift on the main foil and hold elevation above the water)

[0023] FIG. 2 is a diagram illustrating a back plan view of the watercraft that further illustrates the configuration of the watercraft. According to FIG. 2, the watercraft comprises a left elevon, a right elevonand an outboard motor or steering motor. The span of the main foil (beneath the hull) and its struts, as well as the water surface relative to the hull, are depicted.

[0024] In the illustrated embodiment the skim-foiling architecture employs only five powered actuators: two on the elevon control flaps, one on the retractable main-foil strut, and the two standard actuators already present on a commercial outboard motor (power-trim and power-steer). Accordingly, the foiling upgrade adds just three actuators compared with a conventional planing boat, thereby minimising new hardware, weight and cost.

[0025] According to the disclosure, referencing FIGURES 1 and 2, an embodiment of the skim foiling watercraft 100 comprises a hull 110, a propulsion unit 120, a main lifting foil 130, and control surfaces 140L and 140R. The hull 110 can be of a size suitable for recreational use (for example, a 20-30 foot boat) and is preferably a planing-type hull shape with a transom 111 at the stem. The hull includes a bottom surface 112 that, in traditional operation, would plane on the water.

[0026] According to the disclosure, the bottom 112 is largely lifted off the water at speed, but the hull is kept close enough that it can touch down when needed. The propulsion unit 120 in this embodiment is an outboard motor mounted generally at the center of the transom 111. The outboard 120 provides thrust via a propeller 121 (or could be a jet-drive in variants) and is mounted on a swivel bracket that allows it to pivot for steering (arrow 122 indicating yaw rotation) and tilt up or down (arrow 123 indicating trim angle change). The outboard 120 may be an electric motor for an all-electric boat (which is an appealing configuration for eco-friendly, low -noise operation), but the system is equally applicable to gasoline / diesel outboards or inboard-outboard drives - any propulsion that provides a means of steering and trimming.

[0027] The main hydrofoil 130 is positioned under the hull and generally aft of the longitudinal center of gravity (CG) of the loaded boat. In one embodiment, the foil 130 is attached to a retractable stmt assembly. In other embodiments, the main hydrofoil could also be split into two foils (left and right) with one stmt per foil. For example, as shown conceptually in FIG. 1, the foil 130 is mounted to one or more stmts 132 that can move vertically relative to the hull (shown by arrow 133).

[0028] A linear actuator, rotational actuator 134 (FIG. 4) or similar mechanism drives this motion, allowing the foil to be deployed down into the water for operation or retracted upward into a recess 113 in the hull for docking or trailering. In the stowed position, the foil may tuck into a pocket in the hull bottom (possibly behind a step feature in the hull to avoid protruding). In the deployed position, the foil 130 extends below the hull a sufficient depth to generate lift (comparable to the draft of a normal outboard skeg - e.g., 1-2 feet below the hull). The main foil 130 in the preferred design is a fixed geometry wing (no movingflaps on the foil itself). It can be a relatively wide-span, shallow-depth foil that produces lift even just below the surface. The foil may have an upward curve (dihedral or arched shape) so that its tips break the surface at moderate bank angles, providing some passive ventilation effect that limits lift in a bank and thus aids roll stability (similar to the self-stabilizing behavior of surface-piercing foils).

[0029] According to the disclosure, the chord and camber of foil 130 can be optimized for low speeds and to delay cavitation. Notably, because the hull doesn’t rise far, the foil doesn’t need to be very far below the surface - keeping strut lengths short. The foil 130 is generally centered on the boat’s centerline and may have a span wide enough to extend near the port and starboard sides of the hull (as seen in FIG. 2, dashed outline).

[0030] According to the disclosure, the fore -aft position relative to the CG 115 is such that the lift force (arrow L in FIG. 3B) is slightly behind the CG. This creates a natural nose-down pitching moment on the hull (since the lift is pushing up aft of the mass center). In the absence of other forces, this would tend to lower the bow. This inherent moment is deliberately used as a stabilizing tendency: if the boat tilts up too much, the foil’s leverage increases the nose-down pull, discouraging a runaway climb. The magnitude of this moment is designed to be modest - enough to be counteracted by the aerodynamic / hydrodynamic force on the elevons 140L / R when they are appropriately deflected. In essence, the main foil and elevons form a stable trim system akin to an airplane’s wing and tail, with the elevons providing an adjustable counter moment to the foil’s fixed moment.

[0031] At the stem on both the port and starboard sides are the control surfaces 140L and MOR, which are referred to as elevons (FIG. 2). These are akin to small wing flaps or spoilers mounted at the transom edges, one on each side of the outboard 120. In one implementation, each elevon is a plate or foil segment hinged to the hull (or swim platform) such that it can rotate up and down (controlled by an actuator 141L, 141R). They are positioned so that in normal foiling attitude, these elevons are partially submerged - typically their bottom edge is below the water surface.

[0032] By remaining in the water flow, they can exert force on the water: when deflected downward (like an elevator flap), an elevon generates additional lift at the stem (pushing the stem up / nose down), and when deflected upward, it reduces lift at the stem (allowing the nose to rise). By moving them symmetrically, they control the boat’s pitch; by moving them differentially (one up, one down), they control roll. In effect, these are analogous to trim tabs or flaps, but in this design they are actively used during foil- bome operation to balance and stabilize the craft. The elevons 140L / R might be flat plates or could have slight airfoil cross-sections for efficiency. They could be integrated into the transom or attached via smallstruts. In some embodiments, the elevons might double as small buoyant planing surfaces when the hull is in contact with water - for example, if they are shaped like extensions of the hull chines, they could help facilitate a smooth transition onto the foil by providing extra lift at the stem during the hump phase of planing.

[0033] Furthermore, these elevons are fixed-depth (non-retractable) in many designs - since they are at the stem, they don’t typically hinder trailerability much (they can be made robust to withstand some bump or have a simple up-fold hinge if needed). They are also preferably placed at minimal depth to begin with: just deep enough to stay submerged during most mnning conditions (perhaps 6-12 inches below the waterline).

[0034] The combination of elements - main foil 130 aft of CG, twin elevons 140L / R at the stem, and a centrally located propulsion / steering unit 120 - yields a distinctive configuration for the skim foiling system. The elevons essentially act as a tailplane for the boat, providing active stability, while the outboard serves the dual role of thmst and directional control via steering angle

[0035] According to the disclosure, FIG. 1 highlights some of these features in a high-speed skim state: the transom (and elevons) are just at the water surface, the hull bottom ahead of the transom is slightly above the water, and the main foil is below generating lift. FIG. 2 shows how the components are laid out in plan view from the rear. Notably, there are no moving parts on the main foil - all lift modulation and balance is achieved by changing the boat’s angle (which changes foil angle of attack) and by the elevons. This greatly simplifies waterproofing and reliability of the foil assembly.Actuators and Control Hardware

[0036] In one embodiment, the system employs a total of five actuators: two for the elevons 140L, 140R (each driven by an electric linear actuator or servo); one for the main foil retraction mechanism 134; one for motor tilt (many outboards have an integrated hydraulic tilt actuator); and one for motor steering (which could be an optional addon, as traditional steering can be manual via cable / hydraulic linkage). This count is summarized from FIG. 4. Another embodiment could be set-up where there are two non-steerable motors and turning is accomplished by differential thrust (spinning propellers at different speeds). Another embodiment would consist of a main foil split into two half-foils.

[0037] According to the disclosure, only a subset of these need to be under automatic control for basic operation - for example, the core “fly-by-wire” control could involve just the elevon actuators under an electronic control unit, while the human operator controls steering and throttle in the usual way. The flightcontroller (described later) would sense the steering input and boat behavior and adjust the elevons to keep the ride smooth. In more advanced implementations, the steering could also be under electronic control (with the wheel sending signals to a steering servo on the outboard), and the motor tilt could be autoadjusted continuously for optimal trim. The main foil actuator 134 is typically used at specific times (deploying at launch, retracting for shallow water or transit); it could be manually controlled by a switch or automated as part of a mode switch. Another possible embodiment for retraction would be a manual retraction mechanism operated with a lever or a crank, then locked or fixed in place.

[0038] By designing the system such that only 2 new control axes (the two elevons) must be actively and rapidly controlled, one achieves a significant simplification compared to fully actuated foil systems (which might have 4+ control surfaces continuously moving). In essence, the base system adds only “3 actuators beyond a normal planing boat” - the port elevon, starboard elevon, and foil lift (since many planing boats already have power trim and some have power steering).Operation

[0039] According to the disclosure, the operation of the skim foiling recreational boat is similar to the typical hydrofoil, but the main difference is the lower elevation that the boat maintains above the water surface. Because it only tries to foil at a low elevation, the structures (foils, struts, propellers) do not need to extend as far below the boat. This means that the draft of the boat (the lowest point below the water surface) is reduced to that of a traditional planing boat where the lowest point is usually the skeg of the outboard motor or stem drive.

[0040] The amount of lifting force generated by a hydrofoil is proportional to the speed through the water and the angle of attack with respect to the oncoming water. The skim foiling recreational boat relies on the buoyancy of the hull when not in motion. As the motor spins the propeller, it accelerates the boat forward. At this low speed, there is not enough lift generated on the foils to offset the weight of the boat, so it remains fully in contact with the water. The hull picks up speed and transitions to planing. Once the speed of the boat reaches the take-off speed (minimum foiling speed), the foil lift is sufficient to lift the boat hull up and out of the water. At the minimum foiling speed, the angle of attack of the foil relative to the water needs to be large (approximately 5-8 degrees) to generate the required lift. This angle means that the transom of the boat is much lower than the bow of the boat. This geometry is helpful since the submersion of the propeller and elevons at the back of the boat is maximized.

[0041] The pitch angle of the boat (and angle of attack of the main foil) is actively controlled by the elevons acting (changing flap angles) in unison to create pitching (nose up / down) moments on the boat hull. The roll angle (bank left / right) is controlled by moving the elevons differentially.

[0042] The heading angle (direction) of the boat is controlled by steering the outboard motor (or stemdrive) to point the propeller laterally and create a yawing moment. When skimming, the boat will perform a coordinated (banking) turn using a combination of motor steering and elevon differential control inputs. When planing or trolling / docking, the boat will steer as a typical boat by adjusting the angle of the outboard motor (or stemdrive).

[0043] As the skimming boat increases speed, the amount of foil angle of attack (and therefore, boat pitch) required to balance the boat weight decreases and the boat pitch reduces and the boat flattens out. The flight control software works to keep the transom of the boat just above the surface of the water.

[0044] When the boat is ready to be transported via a trailer, the main foil can be retracted up into a recess in the hull, potentially behind a step feature. The outboard motor can be tilted up (as is done typically in COTS outboards), and the elevons could have a rotation feature to swing up and back (similar to the outboard). Now, the boat can be loaded onto a standard trailer for transportation.Operation - Low Speed (Takeoff)

[0045] FIGURES 3A and 3B are diagrams illustrating the operation of the watercraft. FIG. 3A illustrates the watercraft in low-speed skimming operation and FIG. 3B illustrates the watercraft in high-speed skimming operation.

[0046] FIG. 3A is a schematic side view of the watercraft during low-speed operation (displacement / planing mode), prior to foiling. According to FIG. 3A, the hull is partly supported by buoyancy and dynamic lift, with the bow raised and the stem low in the water. When starting from rest, the boat 100 floats with its hull 110 displacing water (the foil 130 alone cannot support it until moving fast).

[0047] The takeoff sequence resembles a normal planing boat. As the throttle is applied, propeller 121 drives the boat forward. Water flows over the hull and foil generates some lift. Initially, the hull provides most of the lift (buoyancy plus planing force), and the boat may go through a hump where the bow rises (point in FIG. 3A). During this phase, the elevons 140L / R can be angled downward to help push the stem up (this is analogous to trim tabs pushing the bow down to get on the plane faster). The main foil 130 at low speed operates at a high angle of attack - the boat is trimmed bow-up, say 5-8° up from level, which means the foil is tilted at a similar angle relative to incoming water.

[0048] This high angle is necessary to generate enough lift at the lower speed. At the takeoff speed (minimum foiling speed, which might be about e.g. 12-15 knots depending on boat weight and foil size), the foil’s lift equals the weight of the boat. At that moment, the foil 130 starts to carry the load and the hull 110 begins to rise out of the water.

[0049] The transition is smooth; as soon as the hull lifts, wetted area (hull drag) drops dramatically, causing a surge in efficiency - the boat can accelerate further with less resistance. The design ensures the propeller and elevons remain submerged during this transition. For that reason, the initial bow-up attitude is actually helpful: it keeps the stem (where the prop and elevons are) deeper in the water at low speed, preventing ventilation.

[0050] The main foil being aft helps here as well, since the boat naturally wants to trim bow -up until the foil takes over. During this phase, the flight controller (or pilot) gradually adjusts the elevons to prevent any sudden pitch-up. Because the foil is behind the CG, as soon as it generates significant lift, it will start exerting a nose-down moment (trying to push the bow down) which counteracts the bow -up tendency from propeller thrust line. The result is that the boat balances into a foiling attitude automatically to some degree, even before active control input, which is a useful self-stabilizing characteristic.Operation - High Speed (Slimming Flight)

[0051] FIG. 3B is a schematic side view of the watercraft during high-speed operation (skim-foiling mode). The hull is lifted clear of the water, riding almost level (flatter pitch) as compared to FIG. 3A, with the foil carrying most of the weight and the elevons keeping the boat trimmed.

[0052] According to FIG. 3B, once at speed, the boat transitions to the skim foiling mode. Here, the hull 110 is entirely out of the water (aside from perhaps some occasional touches or spray). The main foil 130 supports most or all of the weight. As speed increases further above the takeoff point, the foil’s lift would increase (potentially lifting the boat higher), but the control system prevents excessive altitude: the elevons 140L / R are trimmed to adjust the pitch such that the foil generates just enough lift to maintain a target elevation.

[0053] In practice, the “target” is to keep the transom of the hull just inches above the water - essentially skimming. If the boat tends to rise too much (perhaps due to a gust or a rapid acceleration), the controller deflects the elevons downward a bit, which pushes the stem up / bow down, reducing the angle of attack of the main foil and therefore reducing lift - the boat then settles back down.

[0054] Conversely, if the boat starts to drop too low and the hull is about to touch the water, the elevons can be tilted up slightly (allowing the stem to drop relative to the bow), which increases foil angle of attack and lift, raising the boat back up. This forms a closed-loop height control system. Because the hull is so close to the water, even if the control lagged, the hull would gently kiss the water and provide an immediate upward force (and drag) to stop a descent - a very forgiving safety net compared to flying several feet high. During steady cruise the controller holds the bow at ~l-2 deg up trim to minimise foil angle of attack (AoA) and drag.

[0055] According to the disclosure, the flight control system uses inputs from sensors such as an inertial measurement unit (IMU) (monitoring pitch, roll, and heave accelerations) and optionally height sensors. Height above water could be measured by small sonar or lidar units at the stem, or even by a pair of diminutive mechanical wands that skim the surface (one possible embodiment is a short spring-loaded rod attached to each elevon or its stmt, that rotates a potentiometer - as used in some legacy hydrofoil systems for height control). Because the height to maintain is small (on the order of centimeters to tens of centimeters), these sensors can be relatively low-range and compact.

[0056] The control response required is also moderate; the elevons operate in water (which is dense and damps rapid changes) and the system’s natural stability means one may not need extreme control surface deflections. As speed increases, the boat automatically “flattens” its pitch angle - this was observed in experiments. At higher speeds, less angle of attack is needed on the foil for the same lift.

[0057] The controller gradually brings the bow down close to level. In steady cruise, the boat might ride with only a 1-2° bow-up trim. At that point, the elevons might even return to a neutral or near neutral position, and the foil 130 carries the load with the hull gliding just clear of the surface.

[0058] The watercraft in high-speed skimming mode experiences drastically reduced drag (only the stmts 132, foil 130, lower part of outboard 120, and the small elevon surfaces are in the water). For an electric boat, this means much improved range and higher attainable speeds for the given battery capacity. In one estimation, the power consumption in this skim state is comparable to a fully elevated hydrofoil boat on flat water, because nearly all hull drag is eliminated.Turning and Maneuvering

[0059] According to the disclosure, steering the craft can be done just like a normal boat - by turning the outboard motor 120. At low speeds or when not foiling, the hull behaves conventionally (it pivots and turnsvia rudder action of the outboard). When foiling, turning dynamics resemble an aircraft: the boat will bank into a turn. The flight controller can coordinate this by adjusting elevons differentially.

[0060] For example, to initiate a right turn, the operator turns the wheel (or a command from an autopilot) which angles the outboard’s thrust to the right. The craft yaws right, and the controller will simultaneously drop the right-side elevon slightly and raise the left-side elevon - causing the boat to roll right (bank) in concert with the turn, much like an airplane performing a coordinated turn.

[0061] Banking is desirable as it counters centrifugal force and keeps passengers comfortable. The low height means the hull’s bottom comer might touch the water on the inside of the turn, but that can actually serve as a turn assist (akin to a carving turn on a ski - the hull edge contact provides a grip).

[0062] In some embodiments, small turning fins or chines on the hull underside can be provided to improve this contact during aggressive turns. These could be akin to a hydroplane race boat’s turn fins - when the boat banks, a fin on the hull side bites the water to prevent lateral slip. Because our hull never rises far, implementing such features is feasible and can further enhance high-speed turning stability. After the turn, the elevons are leveled again and the boat returns to wings-level skim.Retraction and Shallow Water

[0063] According to the disclosure, when the boat needs to operate in shallow water, or is coming to a dock or being loaded on a trailer, the foil 130 should be retracted. The operator can command foil retraction (or in an advanced system the boat might automatically retract the foil below a certain speed, at a detected water depth, when an impediment or obstacle is detected, or for some other reason). The actuator 134 pulls the stmt(s) 132 up into the hull recess 113.

[0064] In one design, the hull has a small step or cavity such that when retracted the foil’s bottom is flush with or slightly above the keel line - thus it won’t snag when loading onto a trailer. The outboard motor 120 is also tilted up as per normal practice (most outboards have a tilt range that lifts the propeller and skeg out of harm’s way). The elevon flaps 140L / R can either stay as they are (if they don’t protrude below the hull much), or they could be designed with a hinge that allows them to flip up out of the way for storage.

[0065] For instance, an elevon could swing upward and latch, so it doesn’t hang below the hull when not in use. At this point, the boat’s underside has no major projections - it can be handled like a regular boat for trailering or beaching. This ability to quickly revert to a conventional form is a significant practicaladvantage of the system over some fully foiling boats that have intricate folding mechanisms or an inability to fully retract.Control System Architecture

[0066] FIG. 4 is a block diagram of an example control system architecture for the skim foiling boat. It shows the flight controller, various sensors (e.g., inertial measurement unit, speed sensor, height sensors), user controls, and the actuators (for the elevons, motor tilt, steering, and foil lift) that the controller coordinates to maintain stable operation.

[0067] According to FIG. 4, the brain of the system is a flight control unit 150, which may be a marine - grade microcontroller or computer that takes sensor data and outputs actuator commands. The control unit 150 is connected to an IMU 151 (measuring pitch, roll, yaw rates / angles, acceleration), a GPS or speed sensor 152 (for forward speed), and optionally one or more height sensors 153 (e.g., ultrasonic rangefinders at the stem or wand sensors). The unit also monitors the user control inputs 154 - namely steering angle (from the wheel or a steering position sensor on the motor), throttle level, and any mode switches.

[0068] The actuators the flight control unit controls include the port elevon 14 IL, starboard elevon 141R, the foil lift actuator 134, and possibly the trim angle motor 123’ (if the outboard’s trim is motorized and tied in) and steering servo 122’ (if using autopilot or assisted steering). The software in controller 150 uses a control law (which could be a one or more PID controllers or state feedback controller, potentially with feedforward) to maintain desired pitch and height. For example, the controller might target a certain pitch angle and height above water; it compares sensor feedback and adjusts the elevons accordingly.

[0069] According to the disclosure, the system can operate in a manual-assist mode where the pilot is primarily controlling throttle and direction, and the controller simply adjusts elevons to keep the ride smooth (the pilot may not even notice these adjustments). In a fully automated mode, the controller could manage everything: it could, for instance, execute a takeoff by commanding motor trim down, accelerating the foil speed, then trimming up and managing elevons, etc.

[0070] For safety, the system is designed to fail safe - if the controller or actuators fail, the boat will just settle back into hull-borne operation (i.e., the hull will touch the water and behave like a normal boat). The elevons could even be spring biased to return to a neutral position in case of power loss.Adaptability and Retrofits

[0071] According to further embodiments of the disclosure, one additional embodiment is offering the foil and elevon system as a retrofit kit for existing boats. Because the disclosure uses a standard outboard motor as the thrust and primary steering device, many boats could be converted by adding the retractable foilmechanism and integrating a pair of elevon flaps into the stem leveraging the ubiquity of commercial outboards to lower cost and simplify service..

[0072] The elevon actuators and a small flight controller could then be added. This could allow aftermarket upgrading of popular boat models to skim-foiling capability without redesigning the entire boat. The uniqueness of using an existing outboard cannot be overstated - many prior hydrofoil craft use custom propulsion (e.g., submerged electric pods). Furthermore, the ubiquity and reliability of outboards to lower cost and ease maintenance or replacement. The main foil doesn’t interfere with the outboard’s normal function (it is separate and retractable) means one can still use the motor for slow -speed maneuvering and there’s no permanent drag penalty when foils are up (the hull behaves like a normal hull when foil is retracted).Powertrain Variations

[0073] While the preferred embodiment is an electric-powered boat (due to the synergy between efficient foiling and extending electric range), the disclosure is power-source agnostic. It can be implemented on an internal combustion engine boat or a hybrid system as well. For instance, a gasoline outboard could be used in exactly the same manner - the foil and elevon system will improve that boat’s fuel efficiency by reducing drag. In a hybrid, the foil might enable a smaller engine to do the work of a larger one by reducing required power at cruise.Example Use Cases

[0074] In the recreational context, this skim foil boat would allow boaters to have a smoother, more efficient ride on lakes or coastal waters without needing pilot training - the boat essentially auto-stabilizes its height. In a rental fleet scenario, operators could benefit from lower fuel costs and simpler maintenance (fewer complex parts than full foils, and the boat inherently caps its height).

[0075] In a water-taxi or transport context, multiple skim-foiling boats could operate with less wake (since the hull is barely touching water, wave making is reduced) and reduced fuel consumption, while still being easy to service (using known outboard engines).

[0076] For search & rescue or military applications, the advantage would be high speed with lower noise (electric) and shallow draft capability when needed (retract foils to get into shallow zones). In all these cases, the robust simplicity of the system is a selling point - There are fewer components to malfunction in a harsh marine environment.Design Benefits

[0077] According to the disclosure, the aforementioned design provides the following further benefits:• Hydrodynamic Efficiency: Lifting the hull only a few centimeters above the water removes almost all wet areas, reducing wave-making and viscous drag and yielding power-per-knot figures comparable to full-height hydrofoils.• Integrated Stability & Safety: With the main foil positioned aft of the centre of gravity, any excess lift produces a passive nose-down moment, while close proximity of the hull to the surface allows immediate buoyant damping. Active pitch -and-roll control is provided by twin stem elevons; yaw is managed by the steerable propulsion unit.• Mechanical Simplicity: The architecture employs a single fixed-geometry main foil and two small elevons, for a total of approximately five actuators — only three more than a conventional planing boat. No complex multi -foil linkages, hydraulic foil flaps or bespoke propulsion systems are required.• Reduced Sensor and Software Burden: Because the craft operates near the surface, simple feedback from an inertial measurement unit and a low -range height sensor is sufficient; high -cost wave -prediction or radar systems are unnecessary.• Ease of Operation: Take-off, cruise and turning are handled with familiar throttle and steering inputs while the control module automatically trims the elevons, making specialised pilot training unnecessary and limiting the consequences of control error to a gentle hull touchdown.• Versatility and Retrofit Capability: The foil can be retracted, the outboard tilted and the elevons latched upward for shallow -water running, beaching or trailering. The system can be supplied as an OEM feature or as a retrofit kit for existing outboard-powered hulls.• Cost-Effective Manufacturing: Use of commercial off-the-shelf outboard motors, a fixed foil and short struts minimise new tooling, part count and weight, yielding lower production and maintenance costs than high -elevation hydrofoils.• Market Appeal: The craft retains the look and feel of a traditional runabout, making high- efficiency foiling accessible to mainstream recreational, rental and commercial operators, and supporting electric, internal -combustion or hybrid powertrains.• Enhanced Acceleration: Locating the propulsor closer to the centre of gravity reduces nose-up pitching moment during hole -shot, permitting quicker acceleration onto foil.Design Advantages

[0078] According to the disclosure, some advantages of this design are as follows:• Significantly Reduced Drag: By lifting the hull just clear of the water, wetted surface area and wave drag are minimized, yielding much higher propulsive efficiency. On calm water, the power per knot is comparable to full hydrofoil boats, translating to fuel savings or longer electric range.• Lower Mechanical Complexity: The system uses only a single main foil (fixed geometry) and two small flaps, with a total of ~5 actuators (only ~3 new ones beyond a normal boat). No complex multi-foil linkages or heavy hydraulics are required. This simplicity cuts manufacturing cost and maintenance. It also reduces weight, making the system feasible on smaller boats.• Improved Stability & Safety: The hull’s close proximity to the water provides immediate feedback and support. In rough water, if a wave causes a momentary loss of lift, the hull will slap down onto the water, acting as a damper to prevent wild oscillations (whereas a high-flying foil might drop abruptly). The configuration (foil aft of CG, etc.) ensures inherent stability - e.g., if the stem lifts too high (foil over-lifting), a nose-down moment is induced, slowing the boat or submerging the stem elevons more, which corrects the attitude. Additionally, because the boat never flies high, the consequences of any control error are much milder (in effect, it can’t “crash” from a height, it simply splashes down into normal planing).• Ease of Use: The boat can take off and foil automatically without complex user input - a standard throttle up will do, with the system managing trim. Turning does not require special skill (the pilot steers normally; the system handles the banking coordination). The low height means common boating maneuvers remain intuitive - for example, crossing another boat’s wake: a skim foiler will touch the wake like a planing boat. Psychologically, pilots and passengers may feel more comfortable being near the water surface rather than towering above it.• Retained Versatility: The craft still essentially functions as a normal boat when needed. It can operate in shallow water or be beached / trailered by retracting the foil. There is no permanent addition that precludes traditional use - you can still navigate at hull speed under bridges (foil up)or run on plane if needed. The outboard-based propulsion means service and parts are familiar and widely available.• Retrofit and Manufacturing Integration: Because the disclosure can use conventional outboards and mostly self-contained foil modules, manufacturers can integrate this system into existing hull designs without a ground-up redesign. The elevons could be built into new hull molds or added as kits. This lowers the barrier for adoption in the industry. It also makes it harder for competitors to duplicate efficiency without infringing key aspects, since simply bolting generic foils won’t achieve the same controlled skim effect.• Market Appeal: The boat looks and feels more familiar than extreme hydrofoils. From marketing standpoint, it can be pitched as a “next-gen runabout” that is eco-friendly and efficient, rather than an exotic craft. Its lower cost aims to make hydrofoil-like performance affordable to a much wider customer base, including average family boaters. It’s also adaptable to various applications (recreation, rental fleets, fast water taxis, etc.) broadening its market impact.• Reduced Sensor / Software Burden: Unlike fully foiling boats that often require multiple high-end sensors (sonar, radar, etc. for wave sensing) and advanced predictive control algorithms, this system can get by with minimal sensing. The small height makes simple feedback control effective. This not only reduces initial cost but improves robustness (fewer sensitive components that could fail or require calibration).Disadvantages and Limitations

[0079] According to the disclosure, it is acknowledged that the skim-foiling approach has some trade-offs:• Wave Handling: The boat relies on the hull to tackle larger waves. In very rough conditions, a skim foiler will behave more like a normal boat - it will slam waves and experience more drag, whereas a full hydrofoil (if it had long enough struts) could fly over moderate chop smoothly. Thus, the ride advantage diminishes as wave height approaches or exceeds the skim height. Essentially, it can’t completely decouple from wave action beyond a certain sea state.• Height Control Sensitivity: To fully realize the drag reduction, precise height control is needed to keep the hull just out of water without letting it ride too high or touch down too often. This requires a well-tuned control system. Inexperienced operators might find it challenging to manually maintain the optimal trim without assistance. Thus, the automatic control of elevons is an integral part - reliance on this system is a factor (though as noted, failures revert to planing mode). Themargin for error in altitude is smaller than on a long-strut hydrofoil (you only have, say, <1 foot of optimal range). However, the control problem is made easier by the natural stability and damping described earlier.• Efficiency at High Chop: In choppy water where hull contact is frequent, the drag reduction will be less dramatic. The system may repeatedly slap the hull, causing more drag and a less comfortable ride compared to a fully elevated hydrofoil that stays above the wave peaks. So, the performance gains are context-dependent (optimal in mild to moderate chop or calm water, less so in very rough water).• Structural Considerations: The foil being retractable and mounted to the hull (or outboard assembly) means a moving part that must handle significant loads. Proper engineering is needed to ensure the foil strut mechanism is strong and locks securely in place when deployed (to avoid any wobble). Additionally, because the foil is aft, the hull’s structure must carry lift loads somewhat differently (it’s effectively pulling up near the stem); reinforcement of the transom or aft sections may be needed in retrofit cases.• Learning Curve: While it is easier to pilot than a full hydrofoil, the watercraft described herein is still a novel type of boat. Operators will need to leam the “feel” of skim foiling, such as how the boat will settle back onto the hull at very low speeds, or how it banks in turns. Some traditional boaters may require a little time to trust the automated stability system (though it acts in the background).Differences

[0080] The aforementioned skim foiling design has been used in hydrofoiling boats and planing boats.• Full Hydrofoiling Boats: Utilize complex mechanical and hydraulic systems to lift the boat's hull above the water, reducing drag but increasing cost and operational complexity. These lift the hull completely out of water on one or more foils, resulting in very low drag at speed. However, they typically require active control surfaces on the foils or movable foils, plus sensors and computers to manage stability. They also often have multiple foils (e.g., a forward foil and a rear foil) for pitch stability. The complexity drives up cost, and the boats ride high above water which can be unsettling to some users. In contrast, our skim foiler forgoes the last bit of elevation - it doesn’t fly high, thus avoiding the need for large stmts and fast-responding foil flaps. The design achieves efficiency gains with one fixed foil and simpler control (transom flaps). The result is a big drop in mechanicaland electronic complexity (and cost) for a slight sacrifice in absolute performance across varying sea states. For many users and use-cases, this trade-off is beneficial because the boat is cheaper and easier to operate while still drastically improving efficiency (we bridge the gap between planing and foiling).• Traditional Planing Boats: Achieve speed and lift through hull design and engine power but are less efficient and have higher. These rely entirely on the hull shape and engine power to lift partially out of the water at speed. They are simple and robust, but once on a plane they still drag a significant wet area, leading to higher fuel bums and limited speed for a given power. The skim foiler improves upon this by removing almost all hull drag when at speed - essentially it’s like turning a planing hull into a near-hydrofoil once on step. Unlike adding just trim tabs or static fins (which mostly help with planing angles but don’t remove hull drag), our system actually carries the hull’s weight on a wing. Compared to planing boats, tests indicate the skim foiling system offers greatly improved fuel economy or battery endurance (especially at cruise) and a smoother ride in moderate chops (less hull pounding). And when off-foil, the boat still behaves as a normal planing boat, so low-speed handling (docking, etc.) is just as easy. An increase in operational costs is also created due to greater drag.• Foil Assist Kits and Other Hybrids: Some prior art includes partial lift systems - for example, small foils under catamaran hulls or on transom interceptors that reduce wetted area in the range of 40-50%. The current disclosure is estimated to achieve closer to ~90+% reduction in hull wetted area (essentially the whole hull out except maybe a very small area at transom near the elevons). By actively controlling attitude, one improves the performance beyond passive foil assists. The use of an aft-placed main foil with active trim control is unique. Earlier concepts envisioned include a passive pivoting stem foil to stabilize a main foil and multiple static foils. This disclosure effectively inverts that concept whereby a static main foil and small active “stem foils” (elevons) that are easier to control and don’t have to carry full load themselves. This inversion and simplification are a novel approach in the continuum between planing and foiling.

[0081] Compared to full hydrofoiling boats, the skim foiling methodology significantly reduces operational complexity and manufacturing costs by minimizing the elevation height and simplifying the foil and actuation system. This approach makes hydrofoil technology more accessible to the average boater, combining the efficiency benefits of hydrofoiling with the familiarity and simplicity of traditional boating. Unlike traditional planing boats, the skim foiling system offers improved efficiency through reduced dragand energy consumption, providing a greener, cost-effective boating option without sacrificing performance.

[0082] According to the disclosure, as people and cargo move around the boat, the movement of mass can shift the total Center of Mass (COM) around. The location of the main foil needs to be accurately placed so that it exerts the lifting force behind the COM. That will create the nose-down pitching moment that is relied on. The boat design and placement of components needs to be robust to the movement of people and cargo around on the boat deck.

[0083] According to the disclosure, the aforementioned skim foiling system can also be applied to internal combustion engines and / or hybrid electric boats.Further Design Consideration

[0084] The following are further design considerations of interest:• Center of Gravity (CG) and Loading: It is important that the main foil 130 is placed correctly to the boat’s CG 115. As people or cargo move on board, the CG might shift slightly. The design should accommodate this by having some margin in the foil placement and control authority. In general, keeping the main foil lift line just aft of the nominal CG in all loading conditions ensures the boat will always tend to self-correct (nose-down) if lift increases. The elevons and control system can then trim out any steady-state difference. In practice, one might locate the foil about 5- 15% of the boat’s length behind the CG. The boat’s internal layout (battery placement, seating, fuel, etc.) should strive to keep the CG near the design point. If the Center of Mass (COM) moves too far (e.g., everyone runs to the bow), the foil might end up forward of CG which would invert the stability (making it nose-up unstable). Therefore, the specification may include recommended limits on load distribution or even weight sensors to warn if out of balance.• Strut Design: The struts 132 forthe foil could be designed with an airfoil cross-section to minimize drag. They might also be slightly swept to help with ventilation behavior. When retracted, the struts might fold or slide into a recess. In one embodiment, a single central strut attaches to the foil midspan (like a T-foil); in another, two struts attach near foil tips and then join in a “V” shape to the hull. The arrangement can be chosen based on what integrates best with the hull structure.• Elevon Placement: The elevons could be mounted on transom extensions or on outriggers. Ideally, they are placed as far apart (laterally) as possible to maximize roll control moment arm, and as faraft as possible to maximize pitch control moment arm. On some boats, small “blister” pods on the stem could house these flaps. Alternatively, one could integrate them into the outboard’s cavitation plate (though that moves them closer together and might lose some leverage). One chooses transom comers for illustrative purposes due to leverage and ease of mounting.• Failsafe Behavior: The system is preferably designed so that any failure (power, sensor, etc.) does not cause a dangerous situation. This typically means if the controller fails, the elevon actuators either lock or float in a neutral position. The boat will then behave like a normal boat with perhaps a bit of a list or trim change and settle on the hull. Including manual overrides (ability to manually trim the elevons via a switch, etc.) can be a good safety feature. The pilot should also be able to disable foiling mode and force the boat to act as a pure planing boat if needed (maybe by fully retracting the foil and locking elevons neutral).Variations and Alternate Embodiments

[0085] According to the disclosure, while the discussion has focused on a monohull with a single main foil and outboard, alternate embodiments of the disclosure could be adapted to other configurations, including the following:• A twin-hull (catamaran) could employ a similar skim foil concept, with perhaps one foil under each hull or a single foil spanning both hulls, and controlled flaps on each hull’s transom. The stability principles remain, though control might be distributed.• The elevon control surfaces could be replaced or augmented by active trim tabs or interceptor plates at the stem that serve the same purpose (controlling pitch and roll). Essentially, any device that can modulate stem lift could act as the “elevon” in our system.• In an embodiment, the outboard itself could have a small foil attached (for example, a foil on the outboard’s lower unit that provides some lift). Some prior products attach hydrofoil fins to outboards to improve planing. In our context, an outboard -mounted foil could potentially work in conjunction with the main foil - however, care must be taken as the outboard moves for steering. For simplicity, the separate main foil is kept. But in an alternate design, the outboard and foil could be part of one assembly (the “motor / foil assembly” or MFA concept in the original provisional application). This might allow the use of the motor’s tilt actuator to double as foil depth control. For instance, tilting the motor could lift the attached foil out of water. Such variations areconsidered within the scope of this design and can also include the fundamental design elements of skim-height, stability via aft foil & control surfaces.• Another variation is a variable-geometry foil. The disclosure notes that one could employ a foil with a controllable chamber or flap (like aircraft wings have flaps). This could allow adjusting lift characteristics without altering the basic skim foil setup - e.g., a flap on the main foil to fine-tune lift at different speeds. This isn’t necessary in one embodiment, as elevons as used instead, but it’s an option for future refinement and is an anticipated design variation.• The control system could incorporate advanced features like wave sensing (as high-end hydrofoils do) to pre-adjust for waves. Given our lower height, a simpler approach may suffice, but such sensing of waves and variable sea states and coupling this information to the stability control system is another design aspect, especially if operating at the edge of its wave-handling capability.

[0086] According to the disclosure, a watercraft configured for low-elevation hydrofoil operation is disclosed. The watercraft comprises a hull having a bow, a stem and a longitudinal center of gravity (CG) in an operating condition, a primary hydrofoil mounted to an underside of the hull at a location selected to generate lift sufficient to raise the hull out of the water during forward motion of the watercraft, a propulsion arrangement providing forward thrust, at least one set of hydrodynamic control surfaces positioned to remain submerged during foiling and operable, when actuated, to adjust pitch and / or roll of the hull, one or more actuators coupled to the control surfaces, at least one actuator configured to vary a vertical position or angle of the primary hydrofoil relative to the hull, thereby enabling deployment for operation and retraction for shallow- water running or trailering and a control system comprising an electronic controller configured to receive data indicative of watercraft orientation or height above water and to command the control- surface actuators to stabilise pitch and roll while the hull is lifted.

[0087] According to the disclosure, the propulsion arrangement further comprises at least one vectorable propulsor for producing a yaw steering moment or two or more laterally spaced propulsors operable at differential rotational speeds to produce a yaw steering moment.

[0088] According to the disclosure, the primary hydrofoil of the watercraft is attached to a retractable stmt assembly that moves between a deployed position and a retracted position within a hull recess, movement being driven by a linear, rotary or linkage-based actuator. The primary hydrofoil of the watercraft is located aft of the center of gravity such that lift generated by the hydrofoil inherently produces a nose-down pitching moment, and the control surfaces are configured to produce compensating forces to maintain a desired pitch attitude.

[0089] According to the disclosure the hydrodynamic control surfaces comprise port and starboard elevons mounted at or near stem comers of the hull, symmetric deflection of the elevons controlling pitch and differential deflection controlling roll. At least one hydrodynamic control surface is disposed forward of the center of gravity, thereby acting as a canard elevator.

[0090] According to the disclosure, the propulsion arrangement of the watercraft comprises at least one propulsor selected from the group consisting of a steerable outboard motor mounted on a transom of the hull, an inboard / outboard (stem-drive) unit having an articulating drive leg, a water-jet drive with a steerable nozzle, a submerged pod or torpedo drive steerable about a substantially vertical axis or two or more laterally spaced propulsors whose differential rotational speeds generate a yaw moment for steering, wherein each propulsor being located sufficiently close to the waterline, when the hull is in its foiling attitude, to remain submerged without requiring an extended shaft or stmt.

[0091] According to the disclosure, each propulsor of the watercraft is driven by an electric motor, an internal -combustion engine, or a hybrid power unit. The watercraft further comprises an auxiliary hydrofoil rigidly affixed to the steerable outboard motor or a support stmt or housing of the submerged pod or torpedo drive, wherein adjustment of a trim angle of the motor or drive alters an incidence angle of the auxiliary hydrofoil and thereby generates a pitch-control moment.

[0092] According to the disclosure, at least one height sensor of the watercraft is configured to measure distance between a portion of the hull and an underlying water surface, the electronic controller being arranged to use feedback from the height sensor to maintain the hull at a target elevation by actuating the control surfaces.

[0093] According to the disclosure, the electronic controller of the watercraft includes an inertial measurement unit (IMU) and is programmed to deflect the control surfaces symmetrically downward when pitch or height exceed predetermined thresholds, thereby decreasing foil angle of attack, deflect the control surfaces symmetrically upward when pitch or height fall below predetermined thresholds, thereby increasing foil angle of attack and deflect the control surfaces differentially in response to roll deviation.

[0094] According to the disclosure, the control system is configured to coordinate turns by linking control- surface actuation to a steering command so as to bank the watercraft into a turn. The watercraft further comprises at least one stabilizing stmcture on the underside of the hull that engages water when the hull rolls or pitches beyond a predetermined angle and thereby provides damping. Furthermore, the hull, when foiling, rides no more than a predetermined distance above the undisturbed water surface.

[0095] According to the disclosure, a control system for a skim-foiling watercraft, the control system comprises a set of sensors including at least one inertial sensor and at least one height-above -water sensor, a set of actuators including at least two control-surface actuators for adjusting stem-mounted hydrodynamic control surfaces, and a processor configured with control software that maintains the watercraft in a stable foiling state by regulating pitch and roll via the control-surface actuators, and that optionally interfaces with propulsion steering or throttle for assisted or autonomous operation.

[0096] According to the disclosure, a method of operating a watercraft comprising the steps of deploying the primary hydrofoil into the water beneath the hull, accelerating the watercraft forward so that the hull initially planes on the water, continuing acceleration until lift generated by the hydrofoil raises the hull clear of the water, sensing hull pitch and height above water, actuating hydrodynamic control surfaces in response to the sensed parameters so as to stabilise the hull at a target skim height, during a turn, differentially actuating the control surfaces to bank the watercraft and reducing forward thrust below a foiling sustain threshold so that the hull settles back onto the water for displacement or planing operation.

[0097] According to the disclosure, after the hull has settled onto the water, the watercraft further comprising the step of retracting the primary hydrofoil into a hull recess and, where fitted, tilting an outboard motor upward, thereby preparing the watercraft for shallow-water navigation or trailering. Prior to the step of accelerating the watercraft forward, an operator selects a trim setting for an outboard motor and then leaves the trim substantially unchanged while foiling.

[0098] According to the disclosure, the yaw steering of the watercraft is affected solely by differential rotational speeds of at least two laterally spaced propulsors. The primary hydrofoil includes a controllable twist or flap such that roll control is achieved by varying lift distribution across the span, and wherein a single elevator or trim tab disposed at the stem provides pitch control. The primary hydrofoil of the watercraft is formed as two half-span foils, each attached to a respective retractable stmt.

[0099] According to the disclosure, the watercraft when operated in accordance with the method achieves a reduction in propulsive power at a given cmise speed relative to a conventional planing hull of comparable displacement, attributable to reduced wet surface area during the foiling mode.

[0100] According to the disclosure, a watercraft configured for low -elevation hydrofoil operation is disclosed. The watercraft comprises a hull having a bow and a stem and determining a longitudinal center of gravity (CG) when in an operating condition, a primary hydrofoil mounted to an underside of the hull aft of said center of gravity, the primary hydrofoil being configured to generate lift to raise the hull out of water during forward motion of the watercraft, a propulsion and steering unit attached near the stem of thehull, the propulsion unit including a propulsor for driving the watercraft forward and a steering mechanism for turning the watercraft, wherein the propulsion unit is further configured with a trim adjustment to vary a thrust angle relative to the hull, left and right control flaps disposed at or near the stem of the hull on opposite sides of the propulsion unit, each control flap being a hydrodynamic surface pivotable about a horizontal axis to adjust a local lift force, wherein said control flaps are positioned such that during foiling operation they remain generally submerged in the water, one or more actuators operatively connected to said control flaps to actively adjust control flap angles, at least one actuator configured to adjust a vertical position or angle of the primary hydrofoil relative to the hull, with a mechanism for deployment or retraction of the primary hydrofoil, and a control system comprising an electronic controller configured to receive input indicative of the watercraft’s orientation or height above water and to command the control flap actuators to stabilize the watercraft’s pitch and roll.

[0101] According to the disclosure, the primary hydrofoil of the watercraft is attached via a retractable stmt assembly that retracts upward into a recess in the hull and extends downward for operation, thereby allowing the hydrofoil to be deployed for use and stowed for trailering or non -foil operation, whereby the stmt assembly includes a linear actuator to drive retraction and deployment. The primary hydrofoil of the watercraft has a fixed geometry with no movable control surface thereon, and is positioned such that a lift force vector of the hydrofoil acts at a location behind the center of gravity of the watercraft, wherein, when the hydrofoil generates lift, it inherently produces a nose-down pitching moment on the hull, and wherein the control flaps at the stem are configured to produce compensating forces to balance said pitching moment and maintain a desired pitch .

[0102] According to the disclosure, the propulsion and steering unit of the watercraft is an outboard motor mounted on the transom of the hull, the outboard motor providing both thrust and yaw steering. The outboard motor includes a tilt mechanism for trimming its angle, and wherein in the foiling mode of operation, the outboard’s trim angle is adjustable (manually or automatically) to influence the pitch of the watercraft or to assist in lifting the hull. The propulsion and steering unit are an electric motor powered by an onboard battery system, or an internal combustion engine.

[0103] According to the disclosure, each control flap (left and right) is mounted at a stem comer of the hull and configured as an elevon, such that when the flaps are deflected in the same direction (both up or both down) they induce a pitch change, and when deflected differentially (one up, one down) they induce a roll change and the control system is programmed to use symmetric flap deflection to control the ride height (altitude) and pitch angle of the watercraft, and differential deflection to control or damp roll motions.

[0104] According to the disclosure, the watercraft further comprises at least one height sensor oriented to measure distance to the water surface, wherein the sensor is mounted toward an aft portion of the craft whereby the electronic controller uses feedback from said height sensor to maintain the hull at a target elevation above the water by adjusting the control flaps, wherein the height sensor is a small electronic rangefinder device or a mechanical feeler arm that rotates towards the water surface, providing real-time altitude feedback.

[0105] According to the disclosure, the electronic controller includes an inertial measurement unit (IMU) and is configured to perform closed-loop stability control, the controller is further configured to adjust both control flaps downward in unison if the pitch sensor indicates the bow is rising too high or if the height above water exceeds a setpoint thereby pushing the stem up and nose down to reduce lift) and adjust both flaps upward if the bow is too low or hull is descending thereby allowing the stem to drop and nose to rise to increase foil angle of attack and lift, and adjust the flaps differentially in response to roll deviations, to counteract any heeling or bank angle error, wherein the hull is automatically maintained in a substantially level orientation at a small distance above the water surface during forward foiling motion.

[0106] According to the disclosure, the control system of the watercraft is further configured to coordinate turns by linking the flap control with the steering input, wherein when the steering mechanism indicates a turn (e.g., the operator turns the wheel or an autopilot signals a turn), the controller introduces a differential deflection of the left and right flaps to roll the watercraft into the turn, wherein the steering input produces a banked turn and keeps the foil and hull stable, leaning into the bank.

[0107] According to the disclosure, the hull of the watercraft is provided with one or more stabilizing structures that engage the water at certain bank angles or pitch angles to assist stability, the stabilizing structures further comprises small keel fins or chines on the underside of the hull that contact the water when the hull rolls beyond a predetermined angle, providing damping and a restoring moment during sharp turns and a stepped hull profile that helps channel airflow or ventilation under the hull when at foiling speed, reducing suction and aiding smooth re-entry of the hull into water, wherein the keel fins and stepped hulls complement the hydrofoil system by leveraging the hull’s proximity to water for additional stability in dynamic maneuvers.

[0108] According to the disclosure, the primary hydrofoil and control flaps of the watercraft are designed such that the boat’s hull, when foiling, rides no more than a set distance above the undisturbed water surface (measured at the stem).

[0109] According to the disclosure, a control system for an electric-powered skim -foiling boat is disclosed, The control system comprises a set of sensors including at least one of an inertial sensor for measuring boat motions and a height-above-water sensor, a set of actuators including two or more control surface actuators for adjusting stem mounted control flaps of the boat, or a trim actuator for adjusting an outboard motor tilt angle, a processor unit configured with control software, the processor receiving data from the sensors and sending commands to the actuators, wherein the control software is programmed to execute an algorithm that maintains the boat in a stable foiling state by controlling the stem-mounted flaps to regulate pitch and roll, and that optionally adjusts motor trim to regulate overall lift, and wherein the control system has a mode of operation in which only the stem flap actuators are actively controlled while the outboard motor’s steering and throttle are manually controlled by a human operator, such that the system augments a human pilot by automatically “leveling” the boat during foiling or a further mode of operation in which the control system also interfaces with motor steering or throttle to provide a higher level of autonomy or assisted driving .

[0110] According to the disclosure, a method of operating a watercraft equipped with a hydrofoil system and stem control surfaces, the method comprises the steps of accelerating the watercraft forward from rest using a propulsion system so that the hull initially planes on the water, deploying a main lifting hydrofoil into the water beneath the hull, the hydrofoil being located aft of the watercraft’s center of gravity, as the watercraft’s speed increases to a takeoff threshold, generating lift on the hydrofoil sufficient to raise the hull out of the water, sensing the watercraft’s pitch attitude and height above the water surface via onboard sensors, and automatically adjusting a pair of stem-mounted elevon control surfaces in response to the sensed pitch or height, including deflecting said control surfaces downward to arrest upward pitch or limit elevation, and deflecting them upward to correct downward pitch or insufficient elevation, and stabilizing the watercraft at a target skim height where the hull is substantially clear of the water, and during a turn maneuver initiated by the operator or autopilot via a steering input, differentially deflecting said elevon control surfaces (e.g., dropping the inner elevon and raising the outer elevon relative to the turn direction) to bank the watercraft into the turn while maintaining the hull above water, and maintaining the hull in a state of skimming just above the water for the duration of highspeed travel, such that drag is reduced and the watercraft operates in a foiling mode, and upon command or as the watercraft’s speed is reduced below a foiling sustain threshold, lowering the hull back onto the water by reducing hydrofoil lift (which may include retracting the hydrofoil or adjusting control surfaces to set the hull down gently), thereby transitioning the watercraft to a displacement or planing mode for low speed operation or stopping.

[0111] According to the disclosure, the step of automatically adjusting a pair of stem-mounted elevon control surfaces is performed by an electronic flight controller receiving input from an IMU and a waterlevel sensor, and outputting commands to electric actuators attached to each elevon, the controller using a proportional-integral-derivative (PID) control loop or similar feedback mechanism to achieve a stable height with minimal oscillation.

[0112] According to the disclosure, the method further comprising the steps of providing manual or automated control of an outboard motor’s trim angle as part of managing the watercraft’s longitudinal stability, during the acceleration and takeoff phase, trimming the outboard motor downwards to assist in raising the stem and lowering the bow (improving angle of attack for the hydrofoil), and after takeoff, trimming the motor upwards to reduce drag and optimize thrust angle once foiling, wherein the controller or operator dynamically adjusts motor trim in conjunction with elevon adjustments to maintain optimal performance and efficiency.

[0113] According to the disclosure, prior to the step of accelerating the watercraft forward from rest using a propulsion system, the method including the launch preparation steps of extending the hydrofoil from a retracted position to a deployed position and ensuring the control surfaces and system diagnostics are active.

[0114] According to the disclosure, after the step of lowering the hull back onto the water by reducing hydrofoil lift, the method further comprises the step of retracting the hydrofoil into a hull recess, tilting the outboard motor up out of the water; and optionally locking or raising the elevon control surfaces, thereby preparing the watercraft for safe low-speed navigation, beaching, or trailering with appendages minimally projecting below the hull.

[0115] According to the disclosure, when operated according to the method of claim 13, is capable of achieving a state in which the hull is clear of the water surface by a small margin, resulting in a reduction of drag on the hull compared to traditional planing mode at the same speed, thereby significantly increasing fuel efficiency or battery endurance.

[0116] Implementations disclosed herein provide systems, methods and apparatus for generating or augmenting training data sets for machine learning training. The functions described herein may be stored as one or more instructions on a processor-readable or computer-readable medium. The term “computer- readable medium” refers to any available medium that can be accessed by a computer or processor. By way of example, and not limitation, such a medium may comprise RAM, ROM, EEPROM, flash memory, CD- ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. It should be noted that a computer-readable medium may be tangible and non-transitory. As used herein, the term “code” may refer to software, instructions, code or data thatis / are executable by a computing device or processor. A “module” can be considered as a processor executing computer-readable code.

[0117] A processor as described herein can be a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be a controller, or microcontroller, combinations of the same, or the like. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, any of the signal processing algorithms described herein may be implemented in analog circuitry. In some embodiments, a processor can be a graphics processing unit (GPU) . The parallel processing capabilities of GPUs can reduce the amount of time for training and using neural networks (and other machine learning models) compared to central processing units (CPUs). In some embodiments, a processor can be an ASIC including dedicated machine learning circuitry custom-build for one or both of model training and model inference.

[0118] The disclosed or illustrated tasks can be distributed across multiple processors or computing devices of a computer system, including computing devices that are geographically distributed. The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and / or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and / or use of specific steps and / or actions may be modified without departing from the scope of the claims.

[0119] As used herein, the term “plurality” denotes two or more. For example, a plurality of components indicates two or more components. The term “determining” encompasses a wide variety of actions and, therefore, “determining” can include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” can include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” can include resolving, selecting, choosing, establishing and the like.

[0120] The phrase “based on” does not mean “based only on,” unless expressly specified otherwise. In other words, the phrase “based on” describes both “based only on” and “based at least on.” While the foregoing written description of the system enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The system should therefore not be limited by the above-described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the system. Thus, the present disclosure is not intended to be limited to the implementations shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

ClaimsWhat is claimed:

1. A watercraft configured for low-elevation hydrofoil operation, the watercraft comprising: a hull having a bow, a stem and a longitudinal center of gravity (CG) in an operating condition; a primary hydrofoil mounted to an underside of the hull at a location selected to generate lift sufficient to raise the hull out of the water during forward motion of the watercraft; a propulsion arrangement providing forward thrust, the propulsion arrangement further comprising: at least one vectorable propulsor for producing a yaw steering moment; or two or more laterally spaced propulsors operable at differential rotational speeds to produce a yaw steering moment; at least one set of hydrodynamic control surfaces positioned to remain submerged during foiling and operable, when actuated, to adjust pitch and / or roll of the hull; one or more actuators coupled to the control surfaces; at least one actuator configured to vary a vertical position or angle of the primary hydrofoil relative to the hull, thereby enabling deployment for operation and retraction for shallow-water running or trailering; and a control system comprising an electronic controller configured to receive data indicative of watercraft orientation or height above water and to command the control-surface actuators to stabilise pitch and roll while the hull is lifted.

2. The watercraft of claim 1, wherein the primary hydrofoil is attached to a retractable stmt assembly that moves between a deployed position and a retracted position within a hull recess, movement being driven by a linear, rotary or linkage -based actuator.

3. The watercraft of claim 1 or 2, wherein the primary hydrofoil is located aft of the center of gravity such that lift generated by the hydrofoil inherently produces a nose-down pitching moment, and the control surfaces are configured to produce compensating forces to maintain a desired pitch attitude.

4. The watercraft of any preceding claim, wherein the hydrodynamic control surfaces comprise port and starboard elevons mounted at or near stem comers of the hull, symmetric deflection of the elevons controlling pitch and differential deflection controlling roll.

5. The watercraft of any preceding claim, wherein at least one hydrodynamic control surface is disposed forward of the center of gravity, thereby acting as a canard elevator.

6. The watercraft of any preceding claim, wherein the propulsion arrangement comprises at least one propulsor selected from the group consisting of: a steerable outboard motor mounted on a transom of the hull; an inboard / outboard unit having an articulating drive leg; a water-jet drive with a steerable nozzle; a submerged pod or torpedo drive steerable about a substantially vertical axis; or two or more laterally spaced propulsors whose differential rotational speeds generate a yaw moment for steering; wherein each propulsor being located sufficiently close to the waterline, when the hull is in its foiling attitude, to remain submerged without requiring an extended shaft or stmt.

7. The watercraft of claim 6, wherein each propulsor is driven by an electric motor, an internalcombustion engine, or a hybrid power unit.

8. The watercraft of claim 6, further comprising an auxiliary hydrofoil rigidly affixed to the steerable outboard motor or a support stmt or housing of the submerged pod or torpedo drive, wherein adjustment of a trim angle of the motor or drive alters an incidence angle of the auxiliary hydrofoil and thereby generates a pitch-control moment.

9. The watercraft of any preceding claim, further comprising at least one height sensor configured to measure distance between a portion of the hull and an underlying water surface, the electronic controller being arranged to use feedback from the height sensor to maintain the hull at a target elevation by actuating the control surfaces.

10. The watercraft of any preceding claim, wherein the electronic controller includes an inertial measurement unit (IMU) and is programmed to:deflect the control surfaces symmetrically downward when pitch or height exceed predetermined thresholds, thereby decreasing foil angle of attack; deflect the control surfaces symmetrically upward when pitch or height fall below predetermined thresholds, thereby increasing foil angle of attack; and deflect the control surfaces differentially in response to roll deviation.

11. The watercraft of any preceding claim, wherein the control system is configured to coordinate turns by linking control-surface actuation to a steering command so as to bank the watercraft into a turn.

12. The watercraft of any preceding claim, further comprising at least one stabilizing structure on the underside of the hull that engages water when the hull rolls or pitches beyond a predetermined angle and thereby provides damping.

13. The watercraft of any preceding claim, wherein the hull, when foiling, rides no more than a predetermined distance above the undisturbed water surface.

14. A control system for a skim-foiling watercraft, the control system comprising: a set of sensors including at least one inertial sensor and at least one height-above -water sensor; a set of actuators including at least two control-surface actuators for adjusting stem-mounted hydrodynamic control surfaces; and a processor configured with control software that maintains the watercraft in a stable foiling state by regulating pitch and roll via the control-surface actuators, and that optionally interfaces with propulsion steering or throttle for assisted or autonomous operation.

15. A method of operating a watercraft according to any one of claims 1 to 13, the method comprising: deploying the primary hydrofoil into the water beneath the hull; accelerating the watercraft forward so that the hull initially planes on the water; continuing acceleration until the lift generated by the hydrofoil raises the hull clear of the water; sensing hull pitch and height above water; actuating hydrodynamic control surfaces in response to the sensed parameters so as to stabilise the hull at a target skim height; during a turn, differentially actuating the control surfaces to bank the watercraft; andreducing forward thrust below a foiling sustain threshold so that the hull settles back onto the water for displacement or planing operation.

16. The method of claim 15, further comprising, after the hull has settled onto the water, retracting the primary hydrofoil into a hull recess and, where fitted, tilting an outboard motor upward, thereby preparing the watercraft for shallow-water navigation or trailering.

17. The method of claim 15 or 16, wherein prior to step of accelerating the watercraft forward, an operator selects a trim setting for an outboard motor and then leaves the trim substantially unchanged while foiling.

18. The watercraft of any one of claims 1 to 13, wherein yaw steering is affected solely by differential rotational speeds of at least two laterally spaced propulsors.

19. The watercraft of any one of claims 1 to 13, wherein the primary hydrofoil includes a controllable twist or flap such that roll control is achieved by varying lift distribution across the span, and wherein a single elevator or trim tab disposed at the stem provides pitch control.

20. The watercraft of any one of claims 1 to 13, wherein the primary hydrofoil is formed as two half-span foils, each attached to a respective retractable stmt.

21. The watercraft of any one of claims 1 to 13, when operated in accordance with claim 15, achieves a reduction in propulsive power at a given cruise speed relative to a conventional planing hull of comparable displacement, attributable to reduced wet surface area during the foiling mode.

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