Twin hull watercraft

Abstract

Embodiments of the invention provide a displacement hull watercraft that has at least two pontoons, or two pontoon sections in the case of a unitary hull watercraft. The watercraft can recover energy from displaced water to aid in forward motion of the vessel. Advantages are reduced drag through pressure recovery owing to the long, slender stern of the pontoons or pontoon sections. Drag is further reduced at speeds below the hull speed through the close spacing of the pontoons from each other with respect to the pontoon width.

Description

TWIN HULL WATERCRAFT

[0001] The present invention relates to watercraft, particularly to twin hulled watercraft such as catamarans and the like.

[0002] Multihull vessels such as catamarans and pontoon boats are well known and widely used. Advantages can include greater stability, larger deck area, and lower drag as compared to monohull vessels. Examples of catamarans can be found in the following US patents: U.S. Pat. No. 5,191,848A to Roger C. Hatfield for Multihull vessels, including catamarans, with wave piercing hull configuration; U.S. Pat. No. 3,077,850A to William C. Beuby for Sailboat of the catamaran type; and Des. Pat. No. 305,637S to David Emmer for Row boat hull. An example of a pontoon boat can be found in U.S. Pat. No. 5,209,177A to Charles L. Granie et al for Pontoon-type boat.

[0003] The larger deck area possible with multihull vessels make them particularly well suited as automobile ferries. An example of a catamaran type ferry can be found in U.S. Pat. No. 4,304,190A to Nathan I. Daniel for Ferry boat. However, depending on the intended use, a vessel with a narrower overall beam can have the advantages of being more maneuverable and easier to transport out of the water. Examples of catamarans with closely spaced apart pontoons as compared to the width of each pontoon can be found in the following US patents: US8753156B2 to Gregory S. Ketterman et al for Remote Drive; and USD986132S1 to Lyon A. Jantzen for Catamaran.

[0004] The stability and low drag of catamaran type hulls make them well suited for autonomous and semi-autonomous operation, such as in sea drones for environmental monitoring, marine research, waste collection, surveillance and military applications. An example of sea drone can be found is U.S. Pat. No. 7,789,723B2 to Robert A. Dane et al for Unmanned ocean vehicle.

[0005] Multihull hull stand-up paddleboards and catamaran type paddleboards, also known as a standamarans, are known in the art. Advantages can include greater side-to-side stability and buoyancy as compared to single hull paddleboards. Examples can be found in the following US patents: US9248890B2 to Mark Raaphorst for Standup paddleboard system with steering mechanism; and USD662164S1 to Gino Morrelli et al for Stand-up paddleboard.

[0006] Employing a long, slender stern in single hull and multihull vessels can have the advantage of reducing drag through pressure recovery. Examples of single hull and multihull vessels with long sterns and sterns designed for low drag or pressure recovery can be found in the following US patents: USD293096S to Robert N Keller for Sailing vehicle; US996444 to Samual S. Yarrington for Catamaran; and US8122840B2 to Justin A. Harper for Transom stern hull form and appendages for improved hydrodynamics.

[0007] Reducing the length of the mid body so that it is shorter than the stern, or effectively eliminating the mid body by shortening it to zero length, while maintaining the stern and bow at comparable lengths can have the advantage of reducing drag for certain operating speeds. Examples of watercraft with a long stern and a mid body of zero length or short length to reduce drag can be found in the following US patents: US4079688A to George L. Diry for Displacement hull; and US6668743B1 to Zachary M. Reynolds for Semi-displacement hull.

[0008] Thus catamaran type hulls are used in various types of vessels including small, unmanned sea drones, personal human-powered watercraft, pleasure yachts, and large automobile ferries. The large deck area possible with such hull designs can be traded off for increased maneuverability and easier out-of-water transport depending on the intended application. While long, slender sterns can have the advantage of reduced drag through pressure recovery, they trade off buoyancy for a stern of similar height. Likewise, while reducing the length of the mid body can result in reduced drag at certain operating speeds, it also results in less buoyancy for a hull of the same length and height.

[0009] Embodiments of the invention provide a displacement hull watercraft that has at least two pontoons, or two pontoon sections in the case of a unitary hull watercraft. The watercraft can recover energy from displaced water to aid in forward motion of the vessel. Advantages are reduced drag through pressure recovery owing to the long, slender stern of the pontoons or pontoon sections. Drag is further reduced at speeds below the hull speed through the close spacing of the pontoons from each other with respect to the pontoon width. The vessel has low drag under constant speed (e.g. in the case of continuous drive power) and under varying speed or undulating speed (e.g. as in the case of intermittent drive power such as when paddling a human-propelled personal watercraft).

[0010] Experimentation and observation are suggestive that the reduced drag results from further pressure recovery at the inner side surfaces of the sterns in the case where the vessel is powered by a continuous forward drive force. In the case where the vessel is powered by repetitive intermittent pulses of a drive force, such as occurs when paddling a human-powered watercraft, experimentation is suggestive that drag is effectively reduced through energy recovery via interaction of the divergent bow waves between the pontoons and said surfaces of the sterns. Additionally, interaction of transverse waves in the vessel’s wake, which follow the vessel, with inner and outer surfaces of the sterns between pulses of the drive force can aid in propelling the vessel forward, thereby effectively reducing drag when the vessel is powered by repetitive intermittent pulses of a drive force. The effect of the latter depends on the time between pulses where the time between pulses is at least long enough for the transverse wave to catch up to the vessel and interact with said surfaces of the stern.

[0011] Embodiments of the invention provide a watercraft with two pontoons spaced apart and with length and angles of its bow and stern sections configured such that forward motion through a body of water can be aided by the transfer of momentum of the water that is displaced by the forward motion according to three factors under certain conditions. Those factors and conditions are: interaction of the wake from the bow section of one pontoon with the stern section of the other pontoon, and vice versa, when the vessel is gliding and hence its speed is decreasing according to exponential decay; interaction of transverse waves in the wake with the stern sections of the pontoons when the vessel is gliding as each transverse wave overcomes the vessel; and interaction of the stern sections with the displaced water as the water slows down after being displaced by the bow sections and therefore has increased hydrodynamic fluid pressure while the vessel moves forward at a constant speed and when the vessel is gliding.

[0012] According to an aspect of the invention there is provided a watercraft for travel in a body of water. The watercraft has a longitudinal axis and comprises: an elongated deck having a prow at a fore end of the watercraft; and a hull adjoined to the deck. The hull comprises:

[0013] two elongated pontoon sections, each pontoon section having an inner side facing the other pontoon section and an outer side opposite the inner side, an elongated bow section disposed at the fore of the pontoon section and an elongated stern section disposed at the rear of the pontoon section and adjoining the bow section. The inner and outer sides of each pontoon section adjoin at a forwardmost edge of the bow section and are spaced apart at a monotonously increasing distance towards a read end of the bow section. The inner and outer sides of each pontoon section are spaced apart at a maximum distance at a front end of the stern section where the bow and stern sections are adjoined, the maximum distance defining a width of the pontoon section, the width of the pontoon section decreasing towards a rear end of the stern section, and the width of the pontoon section of each pontoon being equal. The inner sides of the pontoon sections are spaced apart at a distance that decreases from the rear end of the stern sections towards the fore of the watercraft, the distance reaching a minimum distance at the front end of the stern section, the minimum distance defining a spacing between the pontoon sections.

[0014] The length of each bow section, the length of each stern section, the width of each pontoon section, and the spacing between the pontoon sections are configured to cause divergent waves emanating from the inner side at the rear end of the bow section of one pontoon section to reach the inner side at the stern section of the other pontoon section when the watercraft is travelling through a body of water in a forward direction along the longitudinal axis of the watercraft.

[0015] Additionally, each bow section has a length equal to a distance from the forwardmost edge of the bow section to the rear end of the bow section, where the length of the bow section of each pontoon may be equal and greater than or equal to one and a half times the width of the pontoon section. Alternatively or in combination, each stern section has a length equal to a distance from the rear end of the stern section to the front end of the stern section, where the length of the stern section of each pontoon may equal and greater than or equal to the length of the bow section. Additionally or in combination, the length of each stern section may be greater than or equal to three times the sum of half the width of one pontoon and the spacing between the pontoon sections.

[0016] Additionally or in combination, the spacing between the pontoon sections may be in a range from one half to two times the width of one pontoon section.

[0017] Additionally or in combination, the deck may have an elongated shape like that of a conventional stand-up paddleboard.

[0018] Additionally or in combination, a fin may be disposed adjacent the rear end of the stern section of each pontoon section to aid in straight tracking as the watercraft travels through the body of water in a forward direction along the longitudinal axis of the watercraft.

[0019] Additionally, the hull and deck may be constructed as a unitary body to reduce manufacturing costs and increase ruggedness of the watercraft among other advantages.

[0020] According to an aspect of the invention there is provided a watercraft that comprises: two elongated pontoons, wherein each pontoon comprises: an elongated bow section at a fore end of the pontoon, the bow section having a length that is the same in each pontoon; an elongated stern section at an aft end of the pontoon, the stern section having a length that is the same in each pontoon; and a mid-section between the bow and stern sections, the mid-section having a length and a width that are the same in each pontoon, wherein the mid-section has an inner side facing the mid-section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides being spaced apart from each other a distance no greater than the width of the mid-section, thereby defining a width of the pontoon, wherein the bow section has an inner side facing the bow section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides adjoining the inner and outer sides of the mid-section, respectively, at one end of the bow section and adjoining each other at the other end of the bow section, wherein the stern section has an inner side facing the stern section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides adjoining the inner and outer sides of the mid-section, respectively, at one end of the stern section and being spaced apart at a distance that decreases towards the other end of the stern section; a superstructure holding the pontoons in a spaced apart arrangement at a distance from each other; and a third pontoon held in position by the superstructure adjacent one of the other pontoons and at a distance that is the same as the distance between the other pontoons, the third pontoon having a bow section and a stern section that have the same length as those of the other pontoons and a width that is the same as the other pontoons.

[0021] An advantage of the third pontoon is increased beam, buoyancy, and lateral stability of the watercraft as compared to watercraft with only two pontoons.

[0022] Additionally, the length of each bow section may be greater than or equal to one and a half times the width of the pontoon. Additionally or in combination, the length of each stern section may be greater than or equal to the sum of the length of one bow section and the length of one mid-section. Additionally or in combination, the distance at which the superstructure holds adjacent pontons may be in a range from one half to two times the width of one pontoon.

[0023] According to an aspect of the invention there is provided, a watercraft that comprises:

[0024] a first pair of two elongated pontoons, each pontoon having an equal width and length, an elongated bow section having a length, and an elongated stern section having a length, the lengths of the bow section of each pontoon being equal and the lengths of the stern section of each pontoon being equal, each stern section having an end that adjoins a respective bow section and a width that decreases towards another end of the stern section; a superstructure holding the pontoons in a spaced apart arrangement at a distance from each other; and a second pair of pontoons, each pontoon of the pair having a bow section and a stern section that have the same length as those of the pontoons in the first pair and a width that is the same as the pontoons in the first pair, and being held in position by the superstructure at a distance from each other that is the same as the distance between the pontoons in the first pair, the second pair of pontoons being held by the superstructure at a spacing from an adjacent one of the pontoons in the first pair that is greater than the distance between the pontoons in the first pair.

[0025] An advantage of the second pair of pontoons is increased beam, buoyancy, and lateral stability of the watercraft as compared to with only one pair of pontoons.

[0026] Additionally, the distance between the pontoons in each pair may be in a range from one half to two times the width of one pontoon. Additionally or in combination, the length of each bow section may be greater than or equal to one and a half times the width of the pontoon, and the length of each stern section may be greater than or equal to the length of each bow section.

[0027] Embodiments of the invention can be advantageously deployed in many applications. For example some embodiments provide increased stability, less drag, and consequently longer glide, straighter tracking, and new uses as compared to conventional stand-up paddleboards.

[0028] Embodiments of the invention can be advantageously deployed as sea drones for the various uses previously described in which sea drones are used. Their low drag and consequent less consumption of energy used to power travel of the vessel would be beneficial in conserving energy, which could enable a reduction in the weight and cost of the drone’s power supply system as well as extending its reach.

[0029] Embodiments of the invention can be advantageously deployed in pleasure watercraft applications as sailing and powered pleasure watercraft and commercial watercraft such as those used as automobile ferries and those for shipping freight. As previously mentioned, their low drag can result in higher speeds of travel for the same drive power, allow for smaller, less costly, and lighter power systems, and extend the distance that can be covered for the same energy expenditure as compared to conventional watercraft of the same type.

[0030] The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

[0031] is an overhead view of a Kelvin wake pattern created by a single hull vessel as it moves forward through water;

[0032] is an overhead view of a wake pattern created by a dual hull vessel in accordance with an embodiment of the invention as it moves forward through water;

[0033] is an overhead view of a wake pattern created by a dual hull vessel in accordance with a preferred embodiment of the invention as it moves forward through water;

[0034] is an overhead view of a wake pattern created by a dual hull vessel in accordance with an embodiment of the invention having pontoons that are spaced wider apart than the embodiment depicted in;

[0035] is an overhead view of a wake pattern created by a dual hull vessel in accordance with an embodiment of the invention having pontoons that are spaced closer together than the embodiment depicted inand having longer mid-sections than the embodiment depicted in;

[0036] is an overhead view of various spacings of the pontoons in embodiments of the invention as compared to the Kelvin wake envelope depicted in;

[0037] is a plan view of a scale model of a dual hull vessel in accordance with a prior art catamaran used for testing and comparison with the performance of embodiments of the invention;

[0038] is a plan view of a scale model of a dual hull vessel in accordance with an embodiment of the invention used for testing and to determine the drag characteristics of the embodiment;

[0039] is a plan view of a dual hull vessel in accordance with an embodiment of the invention having pontoons with a different shape than those of the embodiment ofand used for testing to determine the drag characteristics of the embodiment;

[0040] is a plan view of a dual hull vessel in accordance with an embodiment of the invention having wider pontoons than those of the embodiment ofand used for testing to determine the drag characteristics of the embodiment;

[0041] is an overhead view of a wake pattern created by the embodiment depicted inas it moves forward through water, and which shows the locales of constructive interference of the wakes created by the pontoons in the area between them;

[0042] is a plan view of an embodiment of the invention with a third hull added to the embodiment of;

[0043] is a plan view of an embodiment in accordance with the invention in which two pairs of pontoons of the embodiment inare employed for increased beam and buoyancy of the embodiment.

[0044] is a plan view of an embodiment in accordance with the invention that could be put into use as a stand-up paddleboard;

[0045] is a side view of the embodiment of;

[0046] is a plan view of an embodiment in accordance with the invention that depict an alternative form to the embodiment ofand; and

[0047] is a side view of the embodiment of.

[0048] Like reference characters in the figures denote similar features.

[0049] Referring to, a single hull vessel 10 moves in a forward direction through water with a speed (v), thereby creating a Kelvin wake pattern 11, which includes divergent waves 12 and transverse waves 13. The divergent waves 12 are contained within a Kelvin envelope 14 that is at about 19.5 degrees on either side of the vessel with respect to the forward direction of motion. The divergent waves 12 spread outward and forward on either side of the vessel 10 resulting in wavefronts, or cusp waves 15, that are at an angle of about 53 degrees with respect to the forward direction of motion. The transverse waves 13 move in the same direction as the vessel 10 with the same speed as the vessel 10.

[0050] Referring to, an embodiment of the invention is depicted which is a dual hull vessel 20 having two twin pontoons 21a and 21b. The figure shows the vessel 20 moving in a forward direction through water with a speed (v), thereby creating a Kelvin wake pattern, which includes divergent waves 12 and transverse waves 13. In the figure, only the wake pattern created by the pontoon 21a on the left-hand side of the vessel 20 is shown for clarity. Additionally for clarity, a superstructure the connects the two pontoons 21a, 21b in a fixed position to one another, which position is shown in the figure, has been omitted for clarity. Each of the pontoons 21a, 21b are flat-bottomed with vertical sides, flat tops, and have a height that is half of the width of the pontoon at its widest point. The draft and freeboard are equal, which means the waterline is halfway up the height. Most of the superstructure in embodiments of the invention would remain above the waterline under normal operating conditions, except for operation in rough water conditions or overloading of the vessel 20 beyond its intended carrying capacity. Each pontoon 21a, 21b has a bow section 22 and a stern section 23 separated by a mid-section 24, which in this case has zero length. The stern section 23 is long enough such that divergent waves 12 generated by the opposite pontoon 21b, 21a and that are moving 16 across the area 25 between the two pontoons, contact the stern section 23 causing the divergent waves 12 to be reflected 26 back across the area 25 between the pontoons. This reflection 26 results in a change in the momentum of the divergent wave 12. The change in momentum includes both a change in direction of travel and speed of the divergent wave 12, as well as height and shape of the divergent wave 12, as kinetic energy is transferred from the divergent wave 12 to the opposing pontoon 21b, 21a. This transfer of kinetic energy aids in the forward motion of the vessel 20, thereby decreasing the drag on the vessel 20.

[0051] It should be noted that as a wave moves through water, the water in the wave does not flow in the direction of the travel of the wave but instead moves up at a given point at which a wave crest is approaching and later downward as the wave crest passes that point and the following wave trough approaches.

[0052] The extent to which the transfer of kinetic energy at the stern sections 23 ameliorates the drag depends on the mode of propulsion, that is, the continuous application of a forward driving force versus repetitive impulses of drive force with a resultant exponential decay in the speed of forward travel of the vessel 20 occurring between pulses. The extent to which the drag is reduced also depends on the length of the stern sections 23 and width of the mid-sections 24, which affect the angle of the inner sides of the stern section 23 with respect to the longitudinal axis 28 of each pontoon. The inner sides are the surfaces that face the opposite pontoon 21b, 21a and are adjacent the area 25 between the pontoons 21a, 21b. Longer stern sections 23 that allow the divergent waves 12 to be reflected 26 multiple times by the stern sections 23 further reduce the drag. However, increasing the length of the stern sections 23 also increases the wetted surface area of the vessel 20, which is the area below the waterline, consequently increasing the drag due to increased frictional forces that are directly proportional to the wetted surface area. Therefore, the length of the stern sections 23 must be made to balance the trade-off between positive and negative impacts on drag that result from lengthening the stern sections 23.

[0053] When the vessel 20 is moving at a constant speed (v) and the divergent waves 12 in the area 25 between the pontoons 21a, 21b forms a standing wave pattern, a hydrodynamic pressure gradient exists in the water flowing in the space 25 between the pontoons 21a, 21b. The hydrodynamic pressure is least at the mid-sections 24 where the water is moving the fastest and is greatest at the fore of the bow sections 22 and at the aft of the stern sections 23 where the water is moving the slowest. The hydrodynamic pressure at the stern sections 23 helps to ameliorate the hydrodynamic pressure at the bow sections 22, which opposes the forward motion of the vessel 10. Therefore, the hydrodynamic pressure at the stern sections 23 helps to reduce drag.

[0054] It should be noted that when a vessel having a displacement hull moves through water, the water that is displaced and which is in the immediate vicinity of the hull, and therefore not part of the wake, moves around the hull in a flow. That flow exhibits laminar characteristics at the fore of the bow and becomes increasingly turbulent towards the stern. The point along the hull at which the flow changes from laminar to turbulent flow moves closer to the fore of the bow as the speed of the vessel increases.

[0055] The extent to which the hydrodynamic pressure at the stern sections 23 reduces drag depends on the degree that the water flowing in the area 25 is a laminar flow versus a turbulent flow. Steeper hydrodynamic pressure gradients result in more turbulent flows. When the water flow is more laminar in nature, hydrodynamic pressure will have a greater effect in reducing drag. Longer stern sections 23 and narrower mid-sections 24 , which result in stern sections 23 with inner sides that have a smaller angle with respect to the longitudinal axis of the pontoons 21a, 21b result in flows that are more laminar because the hydrodynamic pressure changes more gradually as the water flows from the mid-sections 24 to the aft of the stern sections 23. However, increasing the length of the stern sections 23 also increases the wetted surface area of the vessel 20, which is the area below the waterline, consequently increasing the drag due to increased frictional forces that are directly proportional to the wetted surface area. Therefore, the length of the stern sections 23 must be made to balance the trade-off between positive and negative impacts on drag that result from lengthening the stern sections 23.

[0056] The speed (v) that the vessel 20 is moving forward through the water also effects the extent to which the hydrodynamic pressure at the stern sections 23 reduces drag. When the vessel 20 is moving forward more quickly, the water flowing in the area 25 will be more turbulent in nature, which results in the kinetic energy in the water being more chaotic and less easily transferred to the vessel 20 through interaction with the surfaces of the inner sides of the stern sections 23.

[0057] In the figures that depict embodiments of the invention, corners at which adjacent sides of a given pontoon 21a, 21b connect are shown as sharp, or angled, transitions. In most cases, embodiments of the invention that are put into practice for normal use, as opposed to testing, would have rounded corners and smooth transitions to reduce drag. Additionally, in the embodiments depicted in the figures the sides of the bow sections, mid-sections, and stern sections are shown as being straight lines. Each side of the bow sections extend from a respective side of the mid-section towards the fore of the vessel and join at a forwardmost point of the bow section, thereby forming a forward edge in the bow section. Likewise, each side of the stern sections extend from a respective side of the mid-section and join at a rearmost point thereby forming a rear edge in the stern section. Embodiments of the invention that are put into practice for normal use, as opposed to testing, could have sides that are slightly curved, in whole or part along the side, especially in the case of the bow and stern sections to form a smooth transition from the respective forward or rear edges to the mid-section to reduce drag. Likewise, the forward and rear edges thus formed could be rounded in such embodiments, to reduce drag, make manufacturing easier and be less prone to defects, and to reduce the possibility of damage to the edges during use of the watercraft.

[0058] Referring to, which depicts a preferred embodiment of the invention, twin pontoons 21a, 21b have a bow section with a length LB, an optional mid-section with a length LM, and a stern section with a length LS. The pontoons further have a width W, are spaced apart by a spacing S, and have a height, or thickness, H (not shown). Each of the pontoons 21a, 21b are flat-bottomed with vertical sides, flat tops, and have a height that is half of the width of the pontoon at its widest point. The draft and freeboard are equal for the designed weight carrying capacity, which means the waterline is halfway up the height. Notes for the determination of the parameters LB,LM,LS,W, S, and H follow below after a description ofto. The result is that LSis greater than or equal to LB(or LBplus LMif there is a mid-section) and the minimum length of the bow section is half of the pontoon width W divided by the tangent of the Kelvin wake angle (i.e. LBmin= (W / 2) / tan(19.47 degrees).

[0059] Referring to, in this embodiment the twin pontoons 21a, 21b are spaced apart by a distance S that results in the divergent waves 12 created by the bow section 22 of pontoon 21a that are propagating in the area 25 between the pontoons 21a, 21b not interacting with the stern section 23 of the opposite pontoon 21b. This is shown by the dash line depicting the Kelvin wake envelope 14 drawn from the forward most point of said bow section 22 to the rearward most point of said stern section 23. Therefore, since there is no reflection 26 of the divergent waves 12 from the surface 27b of stern section 23, there is no transfer of momentum from the divergent waves 12 to the vessel 20. Each of the pontoons 21a, 21b are flat-bottomed with vertical sides, flat tops, and have a height that is half of the width of the pontoon at its widest point. The draft and freeboard are equal, which means the waterline is halfway up the height.

[0060] Referring to, in this embodiment the twin pontoons 21a, 21b are spaced apart by a distance S that results in the divergent waves 12 created by the bow section 22 of pontoon 21a that are propagating in the area 25 between the pontoons 21a, 21b interacting with the stern sections 23 of both pontoons 21a, 21b multiple times. The divergent waves 12 are reflected twice 26, 26’’ by pontoon 21b depicted at points A and C of inner surfaces 29b, 27b of the mid-section 24 and stern section 23, respectively. Likewise, divergent waves 12 are reflected twice 26’, 26’’’ by pontoon 21a depicted at points B and D of inner surfaces 29a, 27a of the mid-section 24 and stern section 23, respectively. However, since the inner surfaces 29a, 29b are parallel to the forward direction of and travel at speed (v), the reflections 26, 26’ from said surfaces 29a, 29b do not aid the forward motion. Due to the angle of the inner surfaces 27a, 27b of the stern section 23, the reflections 26’’, 26’’’ from said surfaces 27a, 27b aid the forward motion. Each of the pontoons 21a, 21b are flat-bottomed with vertical sides, flat tops, and have a height that is half of the width of the pontoon at its widest point. The draft and freeboard are equal, which means the waterline is halfway up the height.

[0061] Referring to, different spacings S, S’, S’’ for the distance between the pontoons 21a, 21b are shown with respect to the Kelvin wake envelope 14. Three positions for the right-hand side pontoon 21b are shown with said pontoon drawn in solid 21b, dashed 21b’ and dotted-dashed 21b’’ lines with the Kelvin wake envelope 14 intersecting the pontoon 21b at intersection points labelled E, F and G, respectively. Point E occurs at the boundary between the bow section 22 and mid-section 24 of pontoon 21b. If the spacing S were reduced, point E would move forward into the bow section 22. That would be undesirable because reflection of the divergent waves 12 at that point would detract from the forward motion of the vessel 20 due to the angle of the inner surface 22b of the bow section 22 with respect to the longitudinal axis 28 of the pontoon 21a. Based on the geometry of the pontoons 21a, 21b with respect to the Kelvin wake envelope 14, the position of point E is also where (W / 2+S) / LBequals tangent(19.5 degrees). The location of point F on the pontoon 21b, depicted in dashed lines 21b’, is at a position on the inner surface 27b of the stern section 23. This position is desirable because reflection of the divergent waves 12 at this position aids in the forward motion of the vessel 20, as previously described. Therefore, based on the geometry of the pontoons 21a, 21b with respect to the Kelvin wake envelope 14, desirable positions of point F fall in the range in which the space S’ between the pontoons 21a, 21b where (W / 2+S’) / (LB+LM) is greater than tangent(19.5 degrees) and where (W+S’’) / L is less than tangent(19.5 degrees). Point G is at the rearmost point on the pontoon 21b, depicted in dotted-dashed lines 21b’’. There is no reflection of divergent waves 12 by the pontoon 21b in this position, as likewise described with respect to. The location of point G is also where (W+S’’) / L equals tangent(19.5 degrees).

[0062] As should be apparent from the description of, that reflection of the divergent waves 12 at inner surfaces 29a, 29b of the mid-sections 24 is not undesirable because they can lead to the divergent waves 12 being later reflected at the inner surfaces 27a, 27b of the stern sections 23, which aid the forward motion of the vessel 20. Therefore, based on the foregoing descriptions associated withto, the desirable range of the space S between the pontoons 21a, 21b is the range in which (W / 2+S) / LBis greater than or equal to tangent(19.5 degrees) and (W+S) / L is less than or equal to tangent(19.5 degrees). For given values of the length LBof the bow section 22, the length L of the vessel 20, and the width W of each pontoon 21a, 21b, and rearranging the foregoing equations, desirable values of the space S between the pontoons 21a, 21b is the range where S is greater than or equal to [tangent(19.5 degrees)*LB-W / 2] to S is less than or equal to [tangent(19.5 degrees)*L-W].

[0063] Some explanation and description of a process that can be followed to derive the configuration of the pontoons, including their dimensions and spacing, for an implementation of an embodiment of the invention is now presented.

[0064] The overall length L and beam of the vessel 20 are selected based on the application of the vessel. Assuming that the superstructure does not extend over the outer sides of the pontoons 21a, 21b, the beam equals the space S between the pontoons plus the width W of each pontoon, that is the beam equals S+2W. The overall length equals the sum of the lengths of the bow section 22, the mid-section 24, and the stern section 23. For example, a stand-up paddleboard typically has a length between 10 and 12 feet, and a beam of 28 to 32 inches.

[0065] The buoyancy B of both pontoons 21a, 21b, that is the sum of the buoyancy of the individual pontoons 21a, 21b, for the intended application is determined. For example, in the case of a stand-up paddleboard, the vessel 20 could be designed for a rider having a weight of 200 lbs or less. In order to have good side-to-side stability, the sum of the buoyancy of the pontoons could be chosen to be twice that of the weight of the rider. Additionally, the superstructure that attaches to the pontoons 21a, 21b and fixedly holds them in their positions with respect to one another could have the same overall shape and dimensions of a conventional paddleboard, but with less thickness (or height). To minimize wetted surface area, the underside of the superstructure should remain above the waterline under normal operating conditions. Additionally, the freeboard of the pontoons, that is distance between the waterline and the top surface of the pontoons, should be enough so that divergent waves 12 propagating in the area 25 between the pontoons have sufficient vertical space to prevent significant deformation of the waves. Experimentation is suggestive that insufficient space, particularly at speeds above the hull speed, will create a “bottleneck” effect for water in the area 25 between the pontoons that increases the drag on the vessel 20. Selecting a buoyancy B that is double the maximum weight of the rider, that is, a buoyancy of 400 lbs should be sufficient to prevent the bottleneck effect at speeds below the hull speed when the space S between the pontoons is greater than or equal to the width W of the pontoons. The freeboard in that case with a rider having the maximum weight of 200 lbs would be half of the height of the pontoons.

[0066] Assuming a constant height H of the pontoons 21a, 21b, and that the pontoons have a simplified shape as into, the height can be calculated from the dimensions of the pontoons and the buoyancy B. For example, when the space S between the pontoons is equal to the width W of the pontoons, then both the space S and width W are equal to the beam length divided by three (i.e., S=W=beam / 3). For the example dimensions, where the beam is 30 inches, the space S between the pontoons and the width W of each pontoon are equal to 10 inches. When the length of the mid-section is zero, the buoyancy B equals the product of the height H, the overall length L, and the width W of each pontoon (i.e., B=H*L*W). When the mid-section has a non-zero length, the height H can be determined from the buoyancy B, the overall length L, the width W of the pontoons, the length LBof the bow section 22, the length LMof the mid-section 24, and the length LSof the stern section 23 by solving the formula B=2H*LM*W+LB*W+LS*W for H.

[0067] Referring to, the length LBof the bow section 22 depends on the width W of the pontoon 21a, 21b. In order that the wake in the area 25 between the pontoons 21a, 21b forms a wake that resembles the Kelvin wake pattern, the length LBof the bow section 22 is chosen so that the angle of either sides 22a, 22b of the bow section 22 with respect to the longitudinal axis 28 of the pontoon 21a, 21b is less than or equal to the angle of the Kelvin wake envelope 14, which is about 19.5 degrees. Therefore, based on the geometry of the shape of the bow section 22, the minimum length LBminof the bow section 22 is (W / 2) / tangent(19.5 degrees). Experimentation and calculations suggest that a good compromise between competing aims such as maximizing buoyancy, reducing drag at the bow section 22, and having a well-formed Kelvin wake in the area 25 between the pontoons 21a, 21b, is to initially choose the length LBof the bow section 22 as being twice the minimum length LBmin. However, this value can be adjusted as the design process can be an iterative one. Approximating tangent(19.5 degrees) as equal to one third, results in the minimum length LBminof the bow section 22 being one and a half times the width W of each pontoon 21a, 21b (i.e., LBmin= 1.5*W) and the initial length LBof the bow section 22 for an iterative design process to be three times the width W of each pontoon 21a, 21b (i.e., LBinital= 3*W).

[0068] Referring again to, the length LMof the mid-section 24 can initially be chosen so that the first point of reflection of the divergent waves 12, at the point labelled A in the figure, is on the inner surface 27b of the stern section 23 slightly aft of the rearmost part of the mid-section 24. Therefore, an initial value for the length LMof the mid-section 24 can be obtained by solving the equation (W / 2+S) / (LB+LM) = tangent(19.5 degrees) in terms of the width W of each pontoon 21a, 21b given the initial values of the space S between the pontoons (i.e. S=W) and the length LBof the bow section 22 (i.e. 3W). Approximating tangent(19.5 degrees) as equal to one third, results in the length LMof the mid-section 24 being one and a half times the width W of each pontoon 21a, 21b (i.e., LMinitial= 1.5*W).

[0069] Referring again to, the length LSof the stern section 23 can initially be chosen by observing that the overall length L of the vessel 20 equals the sum of the length LBof the bow section 22, the length LMof the mid-section 24, and the length LSof the stern section 23. Therefore, by solving the equation L=LB+LM+LSan initial value for the length LSof the stern section 23 can be obtained given the overall length L of the vessel 20 and the initial values for the length LBof the bow section 22 and the length LMof the mid-section 24. Therefore an initial value for the length Ls of the stern section 23 would be the overall length L of the vessel 20 minus the sum of the initial length LBinitalof the bow section 22, the initial length LM initialof the mid-section 24 (i.e., LS initial= L – 4.5*W)

[0070] According to a stand-up paddleboard application, an embodiment of the invention was constructed for a rider having a weight of about 200 lbs. Referring toand, the full length of the vessel 100 was 132” because the superstructure 101 extended past the forwardmost point of the pontoons 21a, 21b by 12”. Therefore, the length L of the pontoons was 120” and the beam of the vessel 100 was 32”. Values of the dimensions of the pontoons 21a, 21b were as follows: L=120”; LB=36”; LS=60”; LM=24”; W=11”; H=4.5”; and S=10”. The superstructure had a thickness (or height) of 1.5” for an overall height of 6” for the vessel 20.

[0071] Testing of scale models of embodiments of the invention proceeded according to the following means and aims: an algebraic determination of design parameters based on known hydrodynamic equations and physics for single, displacement hull vessels as well as some assumptions of physics of the embodiments; use scale model testing to test and confirm design assumptions and to determine performance of various forms and features of the embodiments; testing under constant speed (e.g., drag testing in water tank by applying a constant force and measuring resultant speed) to determine Total Drag (RT); and testing under coasting / gliding conditions (also referred to herein as “Freerun” testing) to determine RTbased on the exponential decay of speed of the embodiment.

[0072] depicts a vessel 30 that is intended to be representative of a prior art catamaran. The vessel 30 has two pontoons 31a, 31b that are the same size and shape, thus are twin pontoons. Each of the pontoons 31a, 31b are flat-bottomed with vertical sides, and flat tops. Each pontoon has a bow section 32, a mid-section 34, and a stern section 33. The mid-section has sides that are parallel to a longitudinal axis 36 of the vessel 30. The vessel 30 includes a superstructure 35 that fixedly holds the pontoons 31a, 31b in position, as shown in the figure. The draft, freeboard, and position of the waterline is dependent on the amount of load carried by the vessel 30 in addition to its own weight. A 4:1 scale model of the vessel 30, which was built for the purposes of scale model testing to determine the drag factor of the design, has the following dimensions: L=42”; LB=12”; LS=1.5”; LM=27”; W=1.5”; H=2.5”; S=4.5”; and WT(beam)=7.5”.

[0073] The weight of the model was 540g. In the data, the vessel 30 is also referred to by the name “Dagger”. The mid-section 34 is longer than the bow section 32, and the stern section is shorter than both the bow section 32 and the mid-section 34. The purpose of this model is to provide a control in testing that has low forward drag due to the sharp bow section 32 but has little to no recovery of energy from the displaced water because of the short stern section 33 and long mid-section 34 in which both sides of each pontoon 31a, 31b are parallel to the longitudinal axis 36 of the vessel 30.

[0074] depicts a vessel 40 that is in accordance with an embodiment of the invention and having two pontoons 41a, 41b with a modified bow section 42 and a stern section 43. The modified bow and stern sections 42, 43 have outer sides 42a, 43a that are parallel to a longitudinal axis 46 of the vessel 40. The vessel 40 includes a superstructure 45 that fixedly holds the pontoons 41a, 41b in position, as shown in the figure. Each of the pontoons 41a, 41b are flat-bottomed with vertical sides, and flat tops. The draft, freeboard, and position of the waterline is dependent on the amount of load carried by the vessel 40 in addition to its own weight. A 4:1 scale model of the vessel 40, which was built for the purposes of scale model testing to determine the drag factor of the design, has the following dimensions: L=42”; LB=9”; LS=33”; LM=0”; W=1.5”; H=2.5; S=2.5”; and WT(beam)=5.5”.

[0075] The weight of the model was 460g. In the data, the vessel 40 is also referred to by the name “Kootemaran or KII”. The vessel 40 has a mid-section 44 of zero length and a stern section 43 that is longer than the bow section 42. The outer sides 42a, 43a of each pontoon 41a, 41b, which are the sides that are opposite the sides that are adjacent to the area 25 between the pontoons 41a, 41b, is parallel to the longitudinal axis 46 of the vessel 40. The inner sides of the bow section 42 of each pontoon, which are the sides adjacent the area 25 between the pontoons 41a, 41b, is angled to channel substantially all the water displaced by the forward motion of the vessel 40 into said area 25 between the pontoons. The purpose of this model is to maximize the recovery of energy from the displaced water. However, that is done at the expense of greater forward drag due to the greater angle of the bow sections 42.

[0076] depicts a vessel 50 that is in accordance with an embodiment of the invention. The vessel 50 has two pontoons 51a, 51b. Each of the pontoons 51a, 51b are flat-bottomed with vertical sides, and flat tops. Each pontoon has a bow section 52, a mid-section 54 of zero length, and a stern section 53. The vessel 50 has a longitudinal axis 56 and includes a superstructure 55 that holds the pontoons 51a, 51b in a fixed position, as shown in the figure, but which can be adjusted to vary the spacing S between the pontoons 51a, 51b within a specified range. This feature of the superstructure 55 is useful during testing to test various spacing of the pontoons at different speeds of travel but could also be beneficial under normal use such as to compensate for adverse effects, or exploit certain conditions, owing to different water conditions and speed of travel. The draft, freeboard, and position of the waterline is dependent on the amount of load carried by the vessel 50 in addition to its own weight. A 4:1 scale model of the vessel 50, which was built for the purposes of scale model testing to determine the drag factor of the design, has the following dimensions: L=36”; LB=8”; LS=28”; LM=0”; W=1.5”; H=2.5”; S=4.5” (default position, with range from 2.5” to 9”); and WT(beam) = 7.5” (default position, with range from 5.5” to 12”).

[0077] The weight of the model was 610g. In the data, the vessel 50 is also referred to by the name “Hybrid A” and also by A5.5, A7.5, and A12 where the numbers 5.5, 7.5, and 12 denote the width of the beam (WT) measured in inches. The Hybrid A model 50 has a mid-section 54 of zero length. The bow sections 52 are similar to those of the Dagger model 30 and the stern sections 53 are similar to those of the Kootemaran model 40. Hence the use of the term Hybrid in the name because the model is a hybrid of the Dagger and Kootemaran models. The purpose of this model 40 is to provide a compromise that benefits from the low forward drag of the Dagger model 30 due to its sharply angled bow sections 32 and also benefits from the energy recovery of the stern sections 43 of the Kootemaran model 40. In this case only about half of the displaced water will be channelled through the area 25 between the pontoons 51a, 51b and hence be available for energy recovery. However, the lower drag of the bow sections 52 more than offsets this compromise.

[0078] depicts a vessel 60 that is in accordance with an embodiment of the invention. The vessel 60 has two pontoons 61a, 61b. Each of the pontoons 61a, 61b are flat-bottomed with vertical sides, and flat tops. Each pontoon has a bow section 62, a mid-section 64 of zero length, and a stern section 63. The vessel 60 has a longitudinal axis 66 and includes a superstructure 65 that holds the pontoons 61a, 61b in a fixed position, as shown in the figure, but which can be adjusted to vary the spacing S between the pontoons 61a, 61b within a specified range. The draft, freeboard, and position of the waterline is dependent on the amount of load carried by the vessel 60 in addition to its own weight. A 4:1 scale model of the vessel 60, which was built for the purposes of scale model testing to determine the drag factor of the design, has the following dimensions: L=36”; LB=12”; LS=24”; LM=0”; W=2”; H=2”; S=3.5” (default position, with range from 1.5” to 8”); WT(beam) = 7.5” (default position, with range from 5.5” to 12”).

[0079] The weight of the model was 610g. In the data, the vessel 60 is also referred to by the name “Hybrid B”. and also by B5.5, B7.5, and B12 where the numbers 5.5, 7.5, and 12 denote the width of the beam (WT) measured in inches. The Hybrid B model 60 is similar to the Hybrid A model 50. There are slight differences in the dimension of the pontoons 61a, 61b and the amount S that they are spaced apart. The purpose of this model 60 is to be able to observe any difference in performance over the Hybrid A model 50 owing to the slightly wider pontoons of the Hybrid B model 60 and its slightly longer bow sections 62 and shorter stern sections 63.

[0080] Referring toto, the outer sides 43a, 53a, 63a of the stern sections 43, 53, 63, are parallel to the longitudinal axis 46, 56, 66 of the vessels 40, 50, 60 and the inner sides 43b, 53b, 63b are angled with respect to said longitudinal axis. The sides that are parallel to the longitudinal axis of each vessel are on the outside of the vessels and the angled sides are on the inside, that is adjacent the area 25 between the pontoons. The reason for the modification to the stern sections is to increase the angle of incidence of the wake from the bow section of the opposite pontoon. This is done to increase the forward component of the incident force of the wake, or hydrodynamic fluid pressure applied to the pontoon, to further aid forward motion of the vessel.

[0081] For the embodiments that were built and tested, the range of the values for the dimensions of the pontoons in terms of the pontoon width W are as follows: LBfrom 3W to 6W; LMfrom 0 to 2.2W; LSfrom 5.5W to 22W; S from 0.75W to 6W; and H from 0.4W to 1.7W.

[0082] Coasting / gliding tests were carried out on the Dagger 30 and Kootemaran models 40 to determine the exponential decay time constant (Tau) of each model. From that the drag factor for the model is calculated from the equation drag factor = total mass / Tau. The testing procedure was to give the model an initial push forward in the testing tank and measure the time (t) at which it reaches a predetermined distance D as well as measuring the total distance (Dmax) that it travels before coming to a stop. The exponential decay time constant (Tau) can then be calculated from the equation D(t) = Dmax[1 – e**(-t / Tau)] since D at time t and Dmaxare known. Other aspects of the test run can be calculated such as the initial speed Vo(e.g. Dmax= Vox Tau) and from that the initial kinetic energy of the model in the test run. Since the test run ends when the model comes to a stop, the average drag force can be calculated based on the kinetic energy lost in the model over the distance it travels (Dmax). Various test runs were executed with different payload weight carried by the models and at different initial speeds. This was done for all four models.

[0083] Continuous speed testing was performed on the Dagger 30 and Kootemaran 40 models. These tests were carried out to determine the drag force experienced by each model as it moves forward through the water under a constant force applied to the model. During each test run the given model goes through a brief period of acceleration until it gets up to a constant maximum speed, at which point the drag force equals the applied force minus a small amount of force lost due to friction in the way the applied force was transmitted to the model. Generally, the Kootemaran model 40 has a higher drag than the Dagger model 30. However, the drags of the two models are closer together than expected after the increased forward drag caused by the bow section 42 of the Kootemaran model is taken into account. However, this increased drag is somewhat offset by the stern section 43 of the Kootemaran model 40 recovering some energy from the displaced water, noting that the difference in wetted surface area of the models and hence the difference in the frictional component of their drags is negligible.

[0084] Glide tests as previously described were performed on the Hybrid A model 50 and Hybrid B models 60, whereby the spacing S between the pontoons was different in the various configurations. The data from test runs with different weights was normalized to a standard total weight of 754 grams (model plus payload). The initial velocity was determined from Dmaxand Tau, as previously described. The peak drag force was determined from calculation of the average drag force. The instantaneous drag force decreases as the speed of the model decreases according to exponential decay. Specifically, the speed can be determined from the equation v(t) = Vo[e**(-t / Tau)] and the drag force from the equation Fdrag(t) = drag factor * v(t) or simply Fdrag(t) = Fdragpeak[e**(-t / Tau)]. Solving these equations for Fdragpeakresults in the peak drag force being twice the average drag force. Regression equations from the data were used to calculate the peak drag force according to the speed of the model in various configurations.

[0085] The drag force was calculated by the regression equations as a function of speed for two configurations each of the Hybrid A and B models 50, 60. The Hybrid B model 60 configurations have lower drag than that of the Hybrid A model 50 configurations. For both models, configurations in which the pontoons spacing S was smallest had the higher drag at the top speeds. The spacing S between the pontoons is the distance between the outer sides of the pontoons at their widest point measured across the longitudinal axis of the vesselminus twice the pontoon width W.

[0086] The term wake used herein refers to displaced water immediately adjacent the bow that has displaced the water as well as divergent waves in the typical Kelvin wake formation. It has been observed that the angle of the wake envelope with respect to the longitudinal axes of the bow section can range from about double the angle of the bow (i.e. longitudinal axis to one side of the bow section) to the typical wake angle of about 19.5 degrees depending on the forward speed of the pontoon.

[0087] Referring to, the wake from each bow section 22 meets in the area 25 between the pontoons 21a, 21b and constructively interfere with each other at locales 70a, 70b, 70c. At higher speeds of travel of the vessel, which speeds produce larger and higher wakes, the two wakes can build up significantly, thereby creating a bottleneck of displaced water that opposes forward motion of the vessel. The first such locale 70a along the longitudinal axis 72 of the vessel where the constructive interference first occurs depends on the bow angle and on the spacing S between the pontoons. Ideally, the shape and spacing of the pontoons should be such that the first such locale 70a, where the constructive interference is the greatest, occurs adjacent the mid-sections 24 or stern sections 23 of the pontoons to avoid the water building up in front of the bow sections of the pontoons, which could more greatly impede forward motion of the vessel (e.g. bottleneck effect). Generally, the spacing between the pontoons S should be at least slightly greater than the width of each pontoon W (e.g. S >= 1.124W), but this is only a guideline. Embodiments of the invention that do not follow this guideline might experience decreased performance under certain operating conditions such as payload weight, speed of travel, and rough water conditions, but still fall under the scope of the claims.

[0088] At a location on the inner side of a pontoon (e.g., the point A in) the wake is deflected into the area between the pontoons. When the vessel is gliding the wake can transfer forward momentum to the pontoon during this deflection depending on the angle of the side of the stern section (with respect to the longitudinal axis of the pontoon) where the contact is made. A larger angle increases the amount of momentum transferred, but for a given pontoon width the length of the stern section LSwill be shorter, which decreases other effects that can aid in propelling the vessel forward. Those effects include multiple interactions with the wake as it is deflected back and forth between the pontoons, the amount of area in the stern section that can receive momentum from a following transverse wave, and the amount of area in the stern section that is exposed to increased hydrodynamic fluid pressure as the displaced water between the pontoons slows down. Generally, the ratio of the length of the stern section LSto the pontoon width W (LS:W) should be in the range 6:1 to 3:1 for a good trade-off between energy transferred to the stern section from the displaced water and wetted surface area, which increases the drag due to frictional forces. However, this range is only a guideline. Embodiments of the invention that do not follow this guideline might experience decreased performance under certain operating conditions such as payload weight, speed of travel, and rough water conditions, but still fall under the scope of the claims.

[0089] The interaction of stern section with the displaced water is speed dependent. For example, variations in drag between Hybrid A / B models with different spacing S between the pontoons varied with speed. Specifically, Hybrid models A and B with 5.5 inch spacing between the pontoons had the least drag at lower speed (i.e. speed below the hull speed) but Hybrid models A and B with wider spacing between the pontoons (e.g. 12 inch, and 7.5 inch, respectively) had less drag at higher speeds (i.e. speeds above the hull speed). One explanation for this observation is that as the speed of travel increases a “bottleneck” effect of passing displaced water between the pontoons increasingly adds drag. This bottleneck effect is dependent on the spacing S between the pontoons, but even with wide spacing (e.g. several times the calculated optimal pontoon width or calculated optimal spacing based on bow angle and length), the long tapered stern shape provides some transfer of energy to aid in the forward motion due to the hydrodynamic fluid pressure applied to the stern of each pontoon.

[0090] Referring to, a triple hull vessel 80 has three pontoons 21a, 21b, 21c having a spacing S between adjacent pontoons. Each pontoon has a bow section 22, a mid-section 24, and a stern section 23 having widths, lengths, and a spacing S from an adjacent pontoon that are in accordance with those described in previous embodiments, for example the embodiments of,, and. The pontoons 21a, 21b, 21c are held in a fixed configuration, as shown in the figure, by a superstructure 81. Generally, a watercraft with three pontoons is known as a trimaran. Advantages of providing a third pontoon 21c are increased buoyancy and beam of the vessel 80 over an embodiment having two pontoons of the same size and shape as those of the vessel 80, while benefitting from the low drag provided through energy recovery of the water displaced in the areas 25, 25’ during forward motion of the vessel 80. Additional pontoons having the same size, shape and spacing from adjacent pontoons can be added to the vessel 80 to form other embodiments with increased buoyancy and beam over this embodiment. This embodiment could be used in applications such as sailing and powered pleasure watercraft and commercial watercraft such as those used as automobile ferries and those for shipping freight.

[0091] Referring to, a vessel 90 has two pairs of pontoons. Each pontoon in a pair 21a, 21b and 21c, 21d has a bow section 22, a mid-section 24, and a stern section 23 having widths, lengths, and a spacing S from an adjacent pontoon in the pair that are in accordance with those described in previous embodiments, for example the embodiments of,, and. The pairs of pontoons are space apart by a distance PS to meet beam and stability requirements of the vessel. Advantages of having spaced apart pairs of pontoons are increased buoyancy, beam, and stability over of the vessel 90 over embodiments having two or three pontoons of the same size and shape as those of the vessel 90, while benefitting from the low drag provided through energy recovery of the water displaced in the areas 25, 25’ between each pair of pontoons during forward motion of the vessel 90. This embodiment could be used in applications such as sailing and powered pleasure watercraft and commercial watercraft such as those used as automobile ferries and those for shipping freight.

[0092] For energy efficient transport, embodiments can make use of an intermittent drive force to take advantage of low drag which gives the vessel excellent glide. Embodiments can make use of impulse drive. For example, an intermittent drive force in which the driving element – for example a propellor – does not have a direct connection to the main driver such as an engine, such that the speed of the drive element is decoupled from the speed of the main driver. The speed of the driving element consequently depends on its own parameters (e.g. weight, shape), load placed on it (i.e., drag of the vessel at a given speed), and the instantaneous energy or force applied to it. Examples include: a paddle connected to an air piston driven by a compressed air tank or connected to a compressed spring, and a propellor coupled to a coil spring with a winding and release mechanism.

[0093] Referring toand, a vessel 100 in accordance with an embodiment of the invention has twin pontoon sections 21a, 21b and a superstructure section 101 that resembles the shape of a conventional stand-up paddleboard. Each pontoon section 21a, 21b has a bow section 22, a mid-section 24, and a stern section 23 having widths, lengths, and a spacing S from the adjacent pontoon section that are in accordance with those described in previous embodiments, for example the embodiments of,, and. The superstructure 101 has a top surface 103a, and a bottom surface 103b. The top surface 103a is intended not to be a wetted surface, that is not in contact or submerged in water, when the vessel 100 is in use when carrying its designed weight capacity, which less than the sum of the buoyancy of both pontoon sections 21a, 21b, under normal water conditions as the vessel 100 moves forward through the water. The bottom surface 103b, is intended to be above the waterline under designed weight loading and normal water conditions, to minimize a frictional component of drag and to minimize the occurrence of the bottleneck effect, which was previously mentioned with respect to. However, embodiments of the vessel 100, wherein the bottom surface 103b is intended to be a wetted surface under designed weight loading and normal water conditions, still fall under the scope of the claims. Normal water conditions would include what are commonly known as calm conditions with minimal waves.

[0094] Each pontoon section 21a, 21b has a fin 102a, 102b, fixedly or optionally removably, attached to the aft of a bottom surface of the stern section 23. The bottom surface is a wetted surface during operation of the vessel 100 in water such that the fin 102a, 102b is substantially or completely submerged in the water so as to act as a rudder, thereby aiding in straight tracking of the vessel 100 is it moves forward in the water. Therefore the fins 102a, 102b aligned to be parallel to a longitudinal axis 104 of the vessel 100.

[0095] The vessel 100 can be of unitary construction, for example from molded plastic or a core body wrapped in fibreglass. The core could be Styrofoam type material, for example expanded polystyrene foam, or a composite core comprising Styrofoam, wood, or other strong lightweight materials such as plastic or aluminum. Alternatively, aside from the fins 102a, 102b, the superstructure 101 and pontoon sections 21a, 21b can be of unitary construction of the type previously mentioned. Additionally, the vessel 100 could be of the same construction as conventional inflatable stand-up paddleboards, such as polyvinyl chloride (PVC) with an air-filled core. Other types of construction are possible, for example a non-unitary body construction, whereby the superstructure 101 and pontoon sections 21a, 21b are constructed in any of the manners previously mentioned and are, fixedly or optionally removably, attached together before sale or use of the vessel 100.

[0096] Referring toand, a vessel 200 in accordance with an embodiment of the invention has twin pontoon sections 21a, 21b and a superstructure section 201 that resembles the shape of a conventional stand-up paddleboard. Each pontoon section 21a, 21b has a bow section 22, a mid-section 24, and a stern section 23 having widths, lengths, and a spacing S from the adjacent pontoon section that are in accordance with those described in previous embodiments, for example the embodiment of. The vessel 200 is an alternative form of the embodiment depicted inandand could be preferrable to that embodiment as being more suitable for unitary construction of the entire vessel 200 or constructing just the superstructure 201 and pontoon sections 21a, 21b as one integral unit. Similar to the vessel 100 ofand, in this embodiment the vessel 200 has two fins 202a, 202b, that are fixedly, or optionally removably, attached to the aft of a bottom surface of the stern section 23 and are aligned parallel to a longitudinal axis 204 of the vessel 200. The superstructure section 201 has a top surface 203a and a bottom surface 203b that are intended to serve during use of the vessel in the same manner as the top and bottom surfaces 103a, 103b as the embodiment ofand. The aft of the stern sections 23 do not extend past the superstructure section 201, which could make the vessel 200 more suitable to be of the same construction as conventional inflatable stand-up paddleboards than the embodiment ofand. The vessel 200 is suitable for construction in any of the manners previously mentioned with respect to the embodiment ofand.

[0097] In view of the many possible embodiments to which the principles of the invention may be applied it should be recognized that the embodiments described herein with respect to the drawings and figures is only illustrative and should not be taken as limiting the scope of the invention.

[0098] For example, the described embodiments have pontoons with flat bottoms and vertical sides. However, other embodiments could have pontoons with rounded bottoms or V-shaped bottoms as is common with many watercraft. Likewise, the sides of the pontoons could slope outwards from bottom to top at any part along a side or along the entire side. The angle of the slope could vary along a side. The bow and stern sections of the pontoons are shown as coming to a point in several embodiments. Other embodiments could have bows that are rounded somewhat at their foremost end and / or could slope forward from bottom to top. The angle could be constant along the forward edge of the bow or vary becoming either less or greater from bottom to top, thereby respectively forming a somewhat convex or concave curved forward edge. Likewise, the stern could be somewhat rounded, flattened, or flat with rounded corners at its rearmost part, and / or could slope forward or backward from bottom to top. As with the bow, the angle could be constant or vary becoming either less or greater from bottom to top, thereby respectively forming a somewhat convex or concave curved surface. Embodiments of the invention are depicted with sharp corners or edges at the juncture of the side, bottom and top surfaces of the bow, mid, and stern sections of the pontoons. However, in other embodiments, any or all of these corners and edges could be rounded to reduce drag, make manufacturing easier and be less prone to defects, and to reduce the possibility of damage to said corners and edges during use of the watercraft. Embodiments of the invention are depicted or described as having two pontoons held in a fixed arrangement by a superstructure. However, other embodiments could have a superstructure that enables the spacing of the pontoons to be varied, as well as the position of the pontoons in a fore or aft direction. Additionally, in other embodiments the pontoons and superstructure could be integrated, thereby forming the watercraft as one integral unit or a bottom hull surface as one integral unit.

[0099] Thus, the scope of the invention should be determined by the appended claims and their legal equivalents as covering all such alterations and modifications that fall within the true scope and spirit of the invention, rather than by the examples given.

Claims

A watercraft for travel in a body of water, the watercraft having a longitudinal axis and comprising:an elongated deck having a prow at a fore end of the watercraft; anda hull adjoined to the deck,wherein the hull comprises:two elongated pontoon sections, each pontoon section having an inner side facing the other pontoon section and an outer side opposite the inner side, an elongated bow section disposed at the fore of the pontoon section and an elongated stern section disposed at the rear of the pontoon section and adjoining the bow section,wherein the inner and outer sides of each pontoon section adjoin at a forwardmost edge of the bow section and are spaced apart at a monotonously increasing distance towards a read end of the bow section,wherein the inner and outer sides of each pontoon section are spaced apart at a maximum distance at a front end of the stern section where the bow and stern sections are adjoined, the maximum distance defining a width of the pontoon section, the width of the pontoon section decreasing towards a rear end of the stern section, and the width of the pontoon section of each pontoon being equal,wherein the inner sides of the pontoon sections are spaced apart at a distance that decreases from the rear end of the stern sections towards the fore of the watercraft, the distance reaching a minimum distance at the front end of the stern section, the minimum distance defining a spacing between the pontoon sections.The watercraft of claim 1, wherein each bow section has a length equal to a distance from the forwardmost edge of the bow section to the rear end of the bow section, the length of the bow section of each pontoon being equal and being greater than or equal to one and a half times the width of the pontoon section.The watercraft of claim 1, wherein each stern section has a length equal to a distance from the rear end of the stern section to the front end of the stern section, the length of the stern section of each pontoon being equal and being greater than or equal to the length of the bow section.The watercraft of claim 3, wherein the length of each stern section is greater than or equal to three times the sum of half the width of one pontoon and the spacing between the pontoon sections.The watercraft of claim 1, wherein the spacing between the pontoon sections is in a range from one half to two times the width of one pontoon section.The watercraft of claim 1, wherein a fin is disposed adjacent the rear end of the stern section of each pontoon section to aid in straight tracking as the watercraft travels through the body of water in a forward direction along the longitudinal axis of the watercraft.The watercraft of claim 1, wherein the hull and deck are constructed as a unitary body.The watercraft of claim 1, wherein the length of each bow section, the length of each stern section, the width of each pontoon section, and the spacing between the pontoon sections are configured to cause divergent waves emanating from the inner side at the rear end of the bow section of one pontoon section to reach the inner side at the stern section of the other pontoon section when the watercraft is travelling through a body of water in a forward direction along the longitudinal axis of the watercraft.A watercraft comprising:two elongated pontoons, wherein each pontoon comprises:an elongated bow section at a fore end of the pontoon, the bow section having a length that is the same in each pontoon;an elongated stern section at an aft end of the pontoon, the stern section having a length that is the same in each pontoon; anda mid-section between the bow and stern sections, the mid-section having a length and a width that are the same in each pontoon,wherein the mid-section has an inner side facing the mid-section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides being spaced apart from each other a distance no greater than the width of the mid-section, thereby defining a width of the pontoon,wherein the bow section has an inner side facing the bow section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides adjoining the inner and outer sides of the mid-section, respectively, at one end of the bow section and adjoining each other at the other end of the bow section,wherein the stern section has an inner side facing the stern section of the other pontoon, and an outer side opposite the inner side, the inner and outer sides adjoining the inner and outer sides of the mid-section, respectively, at one end of the stern section and being spaced apart at a distance that decreases towards the other end of the stern section;a superstructure holding the pontoons in a spaced apart arrangement at a distance from each other; anda third pontoon held in position by the superstructure adjacent one of the other pontoons and at a distance that is the same as the distance between the other pontoons, the third pontoon having a bow section and a stern section that have the same length as those of the other pontoons and a width that is the same as the other pontoons.The watercraft of claim 9, wherein the length of each bow section is greater than or equal to one and a half times the width of the pontoon.The watercraft of claim 9, wherein the length of each stern section is greater than or equal to the sum of the length of one bow section and the length of one mid-section.The watercraft of claim 9, wherein the distance at which the superstructure holds adjacent pontons is in a range from one half to two times the width of one pontoon.A watercraft comprising:a first pair of two elongated pontoons, each pontoon having an equal width and length, an elongated bow section having a length, and an elongated stern section having a length, the lengths of the bow section of each pontoon being equal and the lengths of the stern section of each pontoon being equal, each stern section having an end that adjoins a respective bow section and a width that decreases towards another end of the stern section;a superstructure holding the pontoons in a spaced apart arrangement at a distance from each other; anda second pair of pontoons, each pontoon of the pair having a bow section and a stern section that have the same length as those of the pontoons in the first pair and a width that is the same as the pontoons in the first pair, and being held in position by the superstructure at a distance from each other that is the same as the distance between the pontoons in the first pair, the second pair of pontoons being held by the superstructure at a spacing from an adjacent one of the pontoons in the first pair that is greater than the distance between the pontoons in the first pair.The watercraft of claim 13, wherein the distance between the pontoons in each pair is in a range from one half to two times the width of one pontoon.The watercraft of claim 14, wherein the length of each bow section is greater than or equal to one and a half times the width of the pontoon, and the length of each stern section is greater than or equal to the length of each bow section.

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