Westerbeke WPDS-20 Technical Manual page 9

8
FOUNDATION FOR ENGINE
A good engine bed contributes much
toward the satisfactory operation of the
engine. The engine bed must be of rigid
construction and neither deflect nor twist
when subjected to the engine weight or the
position the boat may have to take under
the effects of rough seas. The bed must
keep the engine within one or two thous-
andths of an inch of this position at all
times. It has to withstand the forward
push of the propeller which is applied to
the propeller shaft, to the thrust washer
bearing in the engine and finally to the
engine bolts and engine bed.
In fiberglas hulls, we recommend that
similar wooden stringers as in wooden
hulls be formed and fitted, then glassed
to the hull securely. This allows hanger
bolts to be installed firmly in wood, thus
reducing noise and transmitted vibration.
The temptation to install the engine on
a pair of fiberglas "angle irons" should
be resisted. Such construction will allow
engine vibrations to pass through to the
hull. Flexible mounts require a firm
foundation against which to react if they
are to do their job. When possible, follow
bed design "A" and avoid bed design "B".
GOOD
A
PROPELLER COUPLING
Each Westerbeke Diesel engine is regu-
larly fitted with a suitable coupling for
connecting the propeller shaft to the
engine.
The coupling must not only transmit the
power of the engine to turn the shaft, but
must also transmit the thrust either ahead
or astern from the shaft to the thrust
bearing which is built into the reduction
gear housing of the engine. This coupling
is very carefully machined for accurate
fit.
For all engine models, a propeller half-
coupling, bored to shaft size for the
specific order, is supplied. The coupling
either has a keyway with set screws or is
of the clamping type.
The forward end of the propeller shaft
has a long straight keyway. Any burrs
should be removed from the shaft end. The
coupling should be a light drive fit on
the shaft and the shaft should not have to
be scraped down or filed in order to get a
fit. It is important that the key be
properly fitted both to the shaft and the
coupling. The key should fit the side of
the keyway very closely, but should not
touch the top of the keyway in the hub of
the coupling.
If it seems difficult to drive the
coupling over the shaft, the coupling can
be expanded by heating in a pail of boil-
ing water. The face of the propeller
coupling must be exactly perpendicular to
the centerline or axis of the propeller
shaft.
PROPELLER
The type and size of propeller varies
with the gear ratio and must be selected
to fit the application based upon boat
tests. To utilize the full power of the
engine, and to achieve ideal loading con-
ditions, it is desirable to use a propel-
ler which will permit the engine to reach
its full rated speed at full throttle
under normal load.
ALIGNMENT OF ENGINE
The engine must be properly and exactly
aligned with the propeller shaft. No
matter what material is used to build a
boat it will be found to be flexible to
some extent and the boat hull will change
its shape to a greater extent than is
usually realized when it is launched and
operated in the water. It is therefore
very important to check the engine align-