Page 280 - Practical Ship Design

238 Chapter 8

Fig. 8.5. Open water cruiser stem.

Angle
down

Wedge Flap

Fig. 8.6. Transom wedge/flap to improve powering performance.

fairly general practice in recent years. The top of the rudder should follow the lines
of the stem with only the necessary clearance.
Keeping the stem immersion to the “desirable” WL position has the added
advantage of permitting the greatest possible propeller diameter for a given draft.
In merchant ships transoms were initially adopted for cost saving reasons, but
once adopted the flat transom concept was progressively developed to provide
more deck area for mooring equipment, to provide stowage for a tier of containers
or to facilitate moving the accommodation further aft. It was also found that a
considerable gain in KM could be obtained by the wider waterlines in the stem,
and there did not seem to be any adverse consequences, at any rate on large ships.
The proviso “on large ships” takes note of the loss of a number of stem trawlers
due to broaching in severe stern seas which may have been due at least in part to the
fact that they had transom sterns.
A transom stern can greatly improve the statical stability of a ship by increasing
the KM but if advantage is taken of this to permit more top weight, the ship may
have inadequate stability when it suffers the big loss in KM which can occur when
the stern comes out of the water when the ship is pitching in a seaway.
Possibly the main argument for retaining a traditional cruiser stern is an
aesthetic one and probably for this reason this type of stern is still featured on some