Propeller Shaft Systems; Propeller Shafts - Volvo Penta TAMD31 Installation Manual

Propeller shafts

When selecting a propeller shaft for a particular appli-
cation, there are many points to be taken into consid-
eration. Shaft material and shaft sizes must suit the
individual vessel designs and application.
The shaft material must have good strength and be
corrosion resistant. A stronger material is beneficial in
many sport cruiser applications, because a smaller di-
ameter results in less underwater resistance and tur-
bulence to the propeller.
Depending on the length, the shaft may need to be
supported with bearings. The minimum distance be-
tween the propeller shaft coupling to the first rigid
bearing should be 6-10 x the shaft diameter. The dis-
tance should be sufficient to allow engine movements
without excessive stresses to the shaft system. The
maximum distance between bearings is determined by
shaft critical speed. This can be calculated based on
the type of installation and shaft properties.
During installation of the shaft, it is of great impor-
tance to protect the precision straightness and fine
surface finish. When lifting shafts it is best to use
slings with spreaders to distribute weight more evenly
to avoid straightness problems.
Always check the straightness of the propeller shaft.
The run-out of the shaft from 100% straightness must
not exceed 0.3 mm per metre ( 0.0036" per foot).

Propeller shaft systems

Single tapered shaft
Double tapered shaft
Shafts that are tapered at both ends, double tapered
shafts, can be machined to be reversible. This effec-
tively doubles the life of the shaft as it can be turned
around when seals and bearings have made wearing
marks in the shaft. Before the shaft is installed, check
the fit of the coupling to the shaft taper.
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