Steerable Tractor Drive Offset Steering Axis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Steering loads caused by high transverse loading from forward-facing propellers in tractor-type marine drives can be significant, particularly during high-speed maneuvers, leading to torque and steering challenges for operators.
Innovation Solution
The steerable tractor-type drive features a gear case pivotally attached to a drive support with a steering axis offset forward of the vertical drive shaft, positioning the propellers forward of the steering axis and ensuring the center of pressure from water flow is rearward of the steering axis, reducing net steering torque through a non-coaxial steering and drive shaft configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If forward-facing propellers are used in tractor-type drives, then propulsive force and speed are improved, but steering loads and torque become excessive
Solution Approach 1:
The patent applies asymmetry by offsetting the steering axis forward of the vertical drive shaft, creating a non-coaxial configuration. This asymmetric arrangement positions the propellers forward of the steering axis, allowing the water flow during turns to generate a center of pressure rearward of the steering axis, which counteracts the excessive steering torque and balances the steering loads.
Solution Approach 2:
The patent changes the geometric parameters of the steering mechanism by offsetting the steering axis from the vertical drive shaft. This parameter change in the spatial relationship between steering and propulsion components creates a moment arm that generates counteracting torque during turns, reducing the net steering force required by the operator.
2Ease of operation
If propellers are positioned forward of the steering axis, then steering torque is reduced, but device complexity increases
Solution Approach 1:
The offset steering axis configuration serves multiple functions simultaneously: it positions the propellers forward of the steering axis to reduce steering torque, creates a center of pressure rearward of the steering axis during turns for counteracting moment, and maintains the structural integrity of the gear case and drive support. This multi-functional design reduces complexity compared to adding separate counterbalance mechanisms.
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 reduces steering torque and net steering forces felt by the operator, improving steering control and reducing the tendency for propellers to continue rotating in the direction of steering, while maintaining the benefits of tractor-type drives such as increased range, speed, and reduced fuel consumption.
Implementation Method 1
a gear case (or drive housing) pivotally attached to the drive support about a steering axis
Implementation Method 2
at least one pulling-type propeller mounted on a propeller shaft extending from a front end of the gear case, the propeller shaft to be rotated by a vertical drive shaft
Implementation Method 3
a center of pressure generated by water rushing past the gear case during a turn is located rearward of the steering axis
Data Source
AI summary
A tractor-type stern drive for a boat includes a drive housing pivotally attached to the stern of the boat about a steering axis. At least one pulling-type propeller is rotatably mounted to a forward end of the gear casing. The at least one propeller is powered by a vertical drive shaft perpendicular to the propeller shaft axis. The steering axis is offset forward of the drive shaft to help minimize steering torque about the steering axis.