Coaxial Contra-Rotating Propellers for Shallow Water Clearance
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Solution Overview
Problem
Current marine vessel propeller designs face challenges in achieving fuel efficiency due to limitations in propeller diameter caused by ship draught constraints, which hinder the utilization of large propellers in shallow waters, leading to suboptimal fuel savings.
Innovation Solution
A marine vessel equipped with a pair of coaxial contra-rotating propellers, where a larger propeller is kept stationary at a specific angular position to maintain clearance above the baseline, allowing a smaller propeller to provide propulsion in shallow waters, while both propellers work together for enhanced hydrodynamic efficiency in deep waters, utilizing a gearbox with a clutch and brake system for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a large propeller diameter is used to reduce kinetic energy loss and improve fuel efficiency, then propeller efficiency is improved, but the propeller cannot be fully submerged in shallow waters due to draught constraints
Solution Approach 1:
The single large propeller is segmented into two contra-rotating propellers of different diameters. The larger first propeller (diameter 1.8-2.2 times the shaft height) provides the main propulsive effect and kinetic energy reduction, while the smaller second propeller (diameter 0.8-1.2 times the shaft height) ensures proper submersion in shallow water. This segmentation allows the system to achieve the benefits of a large propeller while maintaining adaptability to different water depths.
Solution Approach 2:
The solution moves from a single-plane propeller configuration to a three-dimensional tandem arrangement with propellers positioned at different axial locations and rotating in opposite directions. This dimensional change allows the larger first propeller to extend below the baseline for improved efficiency while the smaller second propeller remains above the baseline for shallow water operation.
2Productivity
If a very large propeller extending below the baseline is used to maximize fuel savings, then propeller efficiency is improved, but the vessel cannot operate in shallow waters with full draught
Solution Approach 1:
The system dynamically adapts to different operating conditions through the contra-rotating configuration. In deep water operations, both propellers rotate to maximize fuel efficiency with the large first propeller extending below the baseline. In shallow water, the smaller second propeller ensures adequate clearance above the baseline while the first propeller can be positioned or angled to avoid grounding, providing dynamic adaptability across different water depths.
3Adaptability or versatility
If the first propeller is kept stationary in a specific angular position to maintain clearance, then propulsion in shallow waters is maintained, but the propeller cannot rotate for optimal performance
Solution Approach 1:
The propulsion function is segmented between two propellers with different roles. The first (larger) propeller is optimized for deep water efficiency and can be positioned stationary or at fixed angles when clearance is needed, while the second (smaller) propeller provides the primary propulsion function in shallow water operations. This functional segmentation allows each propeller to operate optimally for its intended purpose.
Solution Approach 2:
The second smaller propeller acts as an intermediary that compensates for the limitations of the first larger propeller in shallow water conditions. When the first propeller cannot rotate or is constrained by clearance requirements, the second propeller mediates by providing sufficient propulsion capability, ensuring continuous operational versatility.
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
This configuration allows for a larger propeller diameter, enhancing propulsive power reduction and maintaining propulsion in shallow waters, achieving significant fuel savings by optimizing propeller efficiency and reducing kinetic energy loss.
Implementation Method 1
The pair of coaxial contra-rotating propellers has a higher hydrodynamic efficiency than a single propeller with the same diameter. The reason is that the tangential velocity component induced by the single propeller does not contribute to the thrust, whereas the tangential velocity component from the forward of the coaxial contra rotating propellers is eliminated by the second propeller, which deflects it aft wards, thereby contributing to the forward thrust.
Data Source
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AI summary
A marine vessel (1) driven by an engine (10, 50) with a very large first propeller (11) and a less large coaxial contra rotating second propeller (12). The marine vessel (1) comprises a hull (2) with a baseline (20) extending between the bow and the aft, an engine (10, 50) arranged inside the hull (2), a pair of coaxial contra-rotating propellers (11, 12) mounted in tandem on concentric shafts (32, 34) at or near the aft of the hull (2) and operably connected to the engine (10). The pair of coaxial contra-rotating propellers (11, 12) comprises a first propeller (11) with a first radius (R1) and a second propeller (12) with a second radius (R2) that is smaller than the first radius (R1). The axis (9) of the concentric shafts (32, 34) has a vertical distance (V) from the base line (20) that is at least equal to the second radius (R2) and smaller than the first radius (R1). Said first propeller (11) being arranged to be kept stationary in a specific angular position whilst the second propeller (12) is rotatable by the large internal combustion engine (10, 50).