Good alignment of the propeller shaft is the starting point
to ensure a low level of noise and vibration on board, and
also to give a reduced stern gear maintenance schedule.
There are many products on the market that try to solve
the problem of good alignment with different systems,
like rubber couplings, Carden units, thrust bearings etc.
The only way to solve the problem is to use constant
velocity joints because they make it possible to rotate the
propeller shaft without transmitting the engine’s movement
and vibrations, but systems on the market at this
moment are often expensive because they demand the
shaft line to be modified and can also require lengthy
installation time.
New SigmaDrive couplings are special cv joints able to
resist to the propeller thrust without the need of thrust
bearings.These couplings are very compact and can
transmitt higher torque than other couplings with similar

Especially designed for yachts and workboats to reduce
or even eliminate noise and vibration, installed at the
same place of standard shaft couplings, they dramatically
reduce or even eliminate noise and vibration that
the engine and propeller transmit to the prop-shaft.

In this diagram we show the traditional system used with 3
fixed points: propeller mount, mechanical seal and gearbox.
Here there are 2 potential causes for vibrations to occur:
- The imperfect alignment of the 3 points that offloads
the eccentric movement on the central point and also
on the engine mounts.
- The oscillations of the engine the are passed directly
down the shaft, that are transmitted directly though the
hull of the vessel.

The improved system with SigmaDrive as opposed to
using traditional shaft mounts, becomes much more
flexible. The coupling corrects imperfect coaxial alignment
between the prop-shaft and the gearbox up to 8° under
torque during use. The engine vibrations are eliminated
and the prop-shaft simply rotates naturally without
transmitting vibrations to the hull, reducing noise and
improving navigation comfort.