Shrouded Propeller Air Gap Drag Reduction
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Solution Overview
Problem
Conventional watercraft propulsion systems lack efficient surface-piercing propellers that can utilize atmospheric air for enhanced performance and integrated steering and trimming mechanisms to reduce drag and improve maneuverability.
Innovation Solution
A propulsion system featuring a surface-piercing propeller surrounded by an annular shroud unit with an air gap above the water level, allowing atmospheric air intake, and integrated steering and trim control sub-systems that pivot and tilt the shroud unit to optimize water flow and reduce drag, utilizing auxiliary trim hydrofoils and guide vanes for enhanced lift and thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional propeller system is used without shrouds, then the device complexity is low, but the drag is high and thrust efficiency is reduced
Solution Approach 1:
The shroud unit is divided into an inner shroud member and an outer shroud member with an air gap between them. This segmentation creates a viscous decoupler that separates water flow, reducing drag on the propeller while maintaining structural feasibility through modular construction
Solution Approach 2:
Atmospheric air is introduced as an intermediary substance between the inner and outer shroud members. The air forms a viscous decoupler layer that mediates the interaction between water flow and the propeller, reducing harmful drag effects while allowing the shroud structure to function effectively
2Power
If a surface-piercing propeller with shroud unit is used, then thrust efficiency is improved, but the device complexity increases
Solution Approach 1:
The shroud unit performs multiple functions simultaneously: it generates hydrodynamic lift to raise the propulsion system above the water surface, provides a viscous decoupler to reduce drag, and directs water flow to the propeller. This multi-functionality achieves high thrust efficiency while avoiding the need for separate dedicated components for each function
Solution Approach 2:
The shroud unit is made dynamically adjustable through integration with steering and trim control subsystems. The ability to pivot and tilt the shroud unit allows it to adapt to different operating conditions, optimizing thrust generation while maintaining structural integrity
3Manufacturing precision
If the shroud unit is made fixed, then the manufacturing precision is easier to achieve, but the adaptability to different operating conditions is reduced
Solution Approach 1:
The shroud unit transitions from a fixed structure to a dynamically adjustable one through integration with steering and trim control subsystems. This allows the shroud to pivot and tilt according to operating conditions, maintaining manufacturing precision in the base structure while adding adaptability through controlled movement
4Productivity
If the propeller is fully submerged, then the propulsion efficiency is maintained, but the drag from water interaction is high
Solution Approach 1:
The viscous decoupler function is extracted from direct water-propeller interaction by introducing atmospheric air into the air gap between shroud members. This creates a protective air layer that isolates the propeller from harmful water drag while maintaining the necessary water flow for propulsion
Solution Approach 2:
Atmospheric air serves as an intermediary substance between the water and the propeller. The air in the air gap creates a viscous decoupler that mediates the interaction, allowing the propeller to operate with reduced drag while maintaining propulsion efficiency through controlled water flow
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
The system achieves reduced drag, increased thrust, and dynamic control of steering and trimming, allowing for efficient propulsion and maneuverability by decoupling water flow with a viscous air layer and utilizing hydrodynamic lift for improved performance.
Implementation Method 1
The inner and outer shroud members define an air gap between them which acts as a viscous decoupler to decouple water flow off the propeller
Implementation Method 2
The outer shroud member has a hydrodynamic lifting formation located at an external side thereof so as to provide hydrodynamic lift as the watercraft travels through water
Implementation Method 3
at least part of the upper portions and thus the air gap defined thereby, is disposed above the water level so that the air gap is exposed to the atmosphere thereby to deliver atmospheric air to the air gap
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A propulsion system 10 for a watercraft, comprises a surface-piercing propeller 12, a propeller drive 14, a shroud unit 16 which surrounds the propeller and a mounting arrangement 18 for mounting the propeller and the shroud unit to a watercraft. The shroud unit comprises an inner shroud 31 and an outer shroud 33 which define leading and trailing ends of the shroud unit and which define an air gap between them in the form of a rearwardly - opening annular recess 34. In use, due to sub-atmospheric pressure conditions created behind the trailing edge of the shroud unit as the watercraft travels through water, air is aspirated into the recess below the waterline, forming a curved sheet of air in the water aft of the shroud unit which decouples water flowing within the shroud from water flow externally thereof, thereby decreasing drag induced by the shroud.