Detachable Hydrojet Inlet Design for Low-Speed Thrust
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Solution Overview
Problem
Existing hydrofoiling watercraft face issues with inefficient thrust at low speeds, debris entanglement in waterjets, difficulty in switching between waterjet and propeller propulsion, and energy inefficiency, particularly in electrically powered systems.
Innovation Solution
A hydrojet propulsion unit designed for easy attachment and detachment from a motor pod, allowing interchange with a propeller system, featuring a conical inlet with fins and a stator to reduce debris entry and operate at lower motor speeds, and a housing design that minimizes vibrations and power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If existing waterjet propulsion units are used in hydrofoiling watercraft, then thrust is generated to propel the watercraft, but the waterjet is not efficient at providing sufficient thrust at low speeds to get the hydrofoiling watercraft up to speed for foiling
Solution Approach 1:
The waterjet propulsion system is divided into separable components: a hydrojet unit that can be detached from the motor pod. This allows optimization of the hydrojet unit specifically for low-speed thrust while using a standard motor pod, resolving the contradiction between generating sufficient low-speed thrust and maintaining system efficiency.
Solution Approach 2:
The hydrojet unit is designed with specific geometric parameters (inlet diameter, outlet diameter, length ratios) optimized for low-speed operation. The inlet diameter is at least 1.25 times the motor pod diameter, and the length from inlet to impeller is at least 1.5 times the impeller diameter, creating optimal flow conditions for low-speed thrust generation.
2Power
If existing waterjets are used in hydrofoiling watercraft, then propulsion is provided, but debris such as seaweed may get caught in the waterjet causing it to cease operation
Solution Approach 1:
The hydrojet unit is designed as a detachable component that can be easily removed from the motor pod. When debris such as seaweed blocks the inlet or wraps around the impeller, the entire hydrojet unit can be quickly detached and replaced, restoring propulsion without complex disassembly procedures.
Solution Approach 2:
The system transitions from a static, permanently installed waterjet to a dynamic, interchangeable hydrojet unit. This allows the propulsion system to adapt to debris conditions by replacing the blocked unit with a clean one, maintaining reliability while keeping the propulsion function.
3Power
If existing waterjet propulsion units are used, then thrust is generated, but the units operate at significantly higher RPMs (6,000-15,000 RPM) compared to propeller-based units (2,000-3,000 RPM)
Solution Approach 1:
The hydrojet unit is designed with optimized geometric parameters including inlet diameter at least 1.25 times the motor pod diameter, outlet diameter at least 1.05 times the motor pod diameter, and length from inlet to impeller at least 1.5 times the impeller diameter. These parameter changes enable the system to operate efficiently at lower RPMs (2,000-3,000 RPM) while maintaining thrust effectiveness, matching propeller operating conditions.
4Power
If existing waterjet propulsion systems are used with electrically powered watercraft, then propulsion is provided, but the waterjet propulsion systems drain the battery more quickly than propeller-based designs
Solution Approach 1:
The hydrojet unit incorporates optimized geometric parameters (inlet diameter ≥1.25× motor pod diameter, outlet diameter ≥1.05× motor pod diameter, length to impeller ≥1.5× impeller diameter) that enable efficient operation at lower RPMs. This reduces power consumption from the battery while maintaining adequate propulsion output, improving energy efficiency for electrically powered watercraft.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient propulsion at lower motor speeds, reduces debris entanglement, and improves energy efficiency, facilitating easy system switching and reducing vibrations and power loss.
Implementation Method 1
The impeller forces the water out rearwardly through a nozzle, creating thrust that drives the watercraft through the water
Implementation Method 2
featuring a conical inlet with fins and a stator to reduce debris entry
Data Source
Figure 1
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AI summary
A personal watercraft is disclosed including a flotation portion, a strut extending from the flotation portion, and a motor pod is disposed along the strut with an electric motor operably coupled to a driveshaft. A hydrojet unit is removably attached to the motor pod and includes an inlet portion removably attached to the motor pod and a substantially cylindrical housing. The inlet portion includes a substantially conical motor interface with a shaft through-hole for receiving the driveshaft therein, one or more fins extending outwardly from the conical motor interface, and at least one ring encircling the conical motor interface and connecting to each of the one or more fins for inhibiting objects from passing through the inlet region. The housing defines a fluid flow path to an outlet portion. The hydrojet unit includes an impeller coupled to the driveshaft and a stator disposed within the housing.