Chapter 1 TPD 1399E
Page 4
Engine bearers
Many types of engine bearer have been found to be
satisfactory in service, including:-
Foam lled f.r.p. with metal plates bonded in, which
are drilled and tapped during engine installation.
Plywood, with epoxy or f.r.p. coating.
Steel channels, attached to bulkheads fore and aft.
Although it is common for the engine mountings to
sit on top of the bearers, in some cases the bearers
are spaced so that the engine ts between the inner
faces, supported by stirrup brackets (A).
Design guidelines
The following rules apply to all bearers:-
The bearers should be capable of supporting a static
load of 5 to 8 times the weight of the engine and
gearbox, to cater for the effects of rough seas.
Cross connections should be arranged to give lateral
rigidity, in order to maintain shaft alignment and to
prevent twisting and racking forces being applied to
the engine.
If the bearers are exible, unwanted vibrations may
be set up in the hull, so the assembly should be made
as stiff as possible.
Close spacing
To enable minimum shaft centre distances to be
achieved in a twin installation, a common centre
bearer supporting the inner mountings of both engines
is sometimes used as shown in (B). By this method
shaft centres down to 630mm may be adopted.
The shaft centres could be reduced further, but this
would result in the engine accessibility becoming very
restricted, and it would be impossible to carry out
service operations.
It should be noted that if minimum shaft centres are to
be adopted, space must be left in front of and behind
the engine to provide access. A minimum clearance
on all sides will mean that the engine cannot be
serviced!
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