Contra-Rotating Marine Drive Gearbox Layout Without Struts or Skegs
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Solution Overview
Problem
Existing marine drive systems with contra-rotating propellers face challenges such as complexity, noise, and the need for struts and skegs, which increase drag and obstruct water flow, while existing transmissions often require the gearbox to be located outside the boat hull.
Innovation Solution
A marine drive assembly with a bevel gear set located above the mounting flange, allowing the gearbox to be housed within the hull, eliminating the need for a strut and enabling direct thrust transfer to the hull, thus reducing drag and noise, and incorporating a lubrication system that utilizes centrifugal force for efficient lubrication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gearbox is located outside the boat hull with struts and skegs, then the contra-rotating propellers can be supported and driven, but drag increases and water flow is obstructed
Solution Approach 1:
The patent merges the gearbox with the hull by locating it inside the hull rather than outside. The drive shaft extends through the hull to connect the engine to the contra-rotating propellers, eliminating the need for external struts and skegs. This integration reduces drag and removes water flow obstructions while maintaining reliable propeller support and drive.
2Ease of manufacture
If the gearbox is located outside the boat hull, then assembly and maintenance may be easier, but noise and vibration increase
Solution Approach 1:
The gearbox is integrated inside the hull, utilizing the hull structure as a natural mounting and damping platform. This placement reduces noise and vibration by isolating the gearbox from the external environment and utilizing the hull's mass and structure for vibration dampening, while still allowing for accessible maintenance through the hull interior.
3Reliability
If a strut is used to support the drive assembly, then the propellers can be properly positioned, but drag increases
Solution Approach 1:
The patent extracts and eliminates the strut from the system by positioning the gearbox inside the hull and extending the drive shaft directly through the hull to the propellers. This removes the drag-generating strut while maintaining proper propeller positioning through the streamlined drive shaft configuration.
4Reliability
If skegs are used to support the drive assembly, then the propellers can be properly positioned, but water flow is obstructed
Solution Approach 1:
The patent extracts and eliminates the skegs from the system by using an internal gearbox configuration with a drive shaft that extends through the hull. This removes the water flow-obstructing skegs while maintaining proper propeller positioning through the streamlined drive shaft and direct coupling to the contra-rotating propellers.
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 solution provides improved thrust efficiency, reduced drag, and enhanced propulsion performance by minimizing noise, vibration, and harshness, while maintaining high efficiency and flexibility for wake shaping in water sports.
Implementation Method 1
incorporating a lubrication system that utilizes centrifugal force for efficient lubrication
Data Source
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AI summary
A marine drive assembly has a housing extending along a central axis and defining a gearbox section and a driveshaft section. A bevel gear assembly is housed in the gearbox section and has a first bevel gear rotatable about a central axis, a second bevel gear rotatable about the central axis, and a third bevel gear rotatable about a radial axis and operatively engaging the first bevel gear and the second bevel gear. A mounting flange is connected to and extends around at least part of the gearbox section. An inner shaft extends along the central axis and is operably connected to the first bevel gear for rotation in a first rotational direction about the central axis. An outer shaft is coaxially arranged with the inner shaft and operably connected to the second bevel gear for rotation in an opposite second rotational direction about the central axis.