Propeller Shafts & Couplings
Propeller Shafts & Couplings:
There a number of designs of propeller shafts, but they all have the following features:
- a solid drive shaft with one end threaded to fit the propeller.
- a lock nut to secure the propeller when it is screwed onto the shaft to enable rotation in either direction without unscrewing the propeller..
- an outer casing that has several functions:
- provides a sealed entry tunnel for the propeller shaft at the propeller end
- to protect and lubricate the drive shaft along its complete length
- provide bearings at each end to support the drive shaft and provide a seal against water entering the inside of the casing
- contain the the thrust of the propeller in both forward and astern directions.This is usually provided by fitting thrust collars that fit firmly against the bearing housings in the tube ends.
We have chosen:
- standardise on the very common 4mm diameter drive shaft (5mm is the most common alternative)
- use brass bearings in the ends of the outer casing (miniature ball bearings are the alternative)
- use stainless steel washers working against the brass bearings for thrust containment.
We offer standard shaft lengths but happily make to any length up to 900mm. After that length, physical problems, called whipping of the drive shaft, can occur which leads to early failure of the drive train. There are solutions to this problem but they need to be considered individually when a drive shaft longer than 900mm is needed..
Special components are required to connect the propeller drive shaft with the engine output shaft (crankshaft). In the case of MSM installations we need fittings for either 5mm or 8mm connections for the engines and a 4mm connection for the propeller shaft. Shaft connection adapters for different sizes can probably be provided on request.
Since it is impractical to exactly align the two drive shafts so that there is no "wobble" in the drive train, we have to provide for a flexible connection that will automatically compensate for alignment variations not only at installation time but also on an ongoing basis. This is done by using two of the universal joint connectors as shown, connected at 90 degrees, to provide smooth transmission of power without unnecessary stress on the drive train.One universal will only smooth out mis-alignments in one plane, two universals set at 90 degrees at their joining fitting will give smooth operation, and minimum wear of the drive train.
A more extensive discussion on this can be found at: