Variable-Pitch Sailboat Propeller Using a Scotch Yoke Feathering Return
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Solution Overview
Problem
Existing marine propellers, particularly feathering propellers, face issues with high hydrodynamic resistance when not in use, require complex disassembly for modifications, and have large dimensions that lead to imbalance and increased cantilever loads on the drive shaft.
Innovation Solution
A variable pitch propeller with a Scotch yoke mechanism that automatically adjusts the blade angle from a feathering to a working position, using a slide and cranks to transform rotational motion into linear motion, allowing for precise pitch adjustment without changing the entire set of blades and reducing the central body's longitudinal dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If feathering propellers are used to reduce hydrodynamic resistance, then the blades can rotate to present minimal surface area to water flow, but the gear system increases internal radial forces and overall longitudinal dimensions
Solution Approach 1:
The patent replaces the traditional gear system (conical wheels) with a Scotch yoke mechanism that uses a slide and crank to transform rotational motion into linear motion for blade pitch adjustment. This substitution eliminates the need for complex gear trains, reducing internal radial forces and longitudinal dimensions of the central body while maintaining the feathering function.
Solution Approach 2:
The invention extracts and eliminates the gear transmission system from the propeller design, using only the essential Scotch yoke components (slide, crank, and blade attachment) to achieve pitch control. This removal of unnecessary mechanical elements reduces the overall longitudinal dimensions and internal forces.
2Object-affected harmful factors
If folding propellers are used to minimize hydrodynamic resistance, then blades fold back towards the stern, but this creates larger overall dimensions and imbalance of masses on the drive shaft
Solution Approach 1:
The patent uses asymmetric blade profiles and strategic placement of counterweights on the drive shaft to compensate for the mass distribution created by the folding blade mechanism. This asymmetric design approach maintains balance while allowing blades to fold back for minimal resistance.
3Power
If fixed pitch propellers are used for motor travel efficiency, then blades are oriented for optimal thrust, but this creates high aerodynamic resistance when motor is switched off
Solution Approach 1:
The patent implements a dynamic pitch adjustment mechanism using the Scotch yoke system that allows blades to automatically change orientation based on operational mode. During motor travel, blades are positioned for optimal thrust; during sailing, the mechanism rotates blades to a feathered position minimizing resistance, eliminating the need for separate fixed-pitch and folding propellers.
4Adaptability or versatility
If feathering propellers with gear systems are used, then blade orientation can be adjusted, but the system generates internal radial forces impacting the central body
Solution Approach 1:
The patent replaces the gear system with a Scotch yoke mechanism where a slide moves linearly within the central body while a crank converts this linear motion into rotational motion for blade pitch adjustment. This substitution eliminates meshing gears that generate radial forces, reducing impact on the central body while maintaining full blade orientation adjustability.
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 propeller achieves reduced hydrodynamic resistance, simplified pitch modification, and reduced overhanging loads on the drive shaft, enhancing maneuverability and reducing the need for complex disassembly, while maintaining precise control over blade angles.
Implementation Method 1
a mechanism of the Scotch yoke type for the transmission and transformation, in an automatic manner, of the rotary motion of the drive shaft (2) into inclination motion of the propeller blades (5)
Implementation Method 2
a spring in compression which guarantees the return, when the motor is switched off, of the propeller to the feathering position
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
A variable pitch propeller (100) is described, comprising an external central body (10-11) and a plurality of rotatable blades (5), protruding from said central body (10-11), said central body (10-11) housing, in its interior, a hub (1) of a drive shaft (2) which is placed coaxial to said hub (1), said central body (10-11) housing in its interior a device to transform, in an automatic manner, the rotary motion of said hub (1) or of said drive shaft (2) into rotary motion of said at least one blade (5) around its axis with respect to said body of said propeller (100), said device being coupled to at least one of said blades (5) and to said hub (1) or to said drive shaft (2), characterised in that said device is a modified Scottish yoke kinematic system contained inside said central body (10-11).