Page 70 - Introduction to Naval Architecture

FLOTATION AND STABILITY

Hydrostatic data: KG= 8.5 m, KM= 9.3 m, MCT 1 m = 105 MNm,
LCF = 2.7m aft of amidships.

Solution
Trim lost when touching down

Distance from heel of sternframe to LCF

Moment applied to ship when touching down
Trimming moment lost by
ship when touching down
Hence, thrust on keel, w

Loss of GMwhen touching down

Metacentric height when touching down

LAUNCHING

The launch is an occasion in the ship's life when the buoyancy, stability,
and strength, must be studied with care. If the ship has been built in a
dry dock the 'launch' is like an undocking except that the ship is only
partially complete and the weights built in must be carefully assessed to
establish the displacement and centre of gravity position. Large ships
are quite often nowadays built in docks but in the more general case
the ship is launched down inclined ways and one end, usually the stern,
enters the water first. The analysis may be complicated by the launching
ways being curved in the longitudinal direction to increase the rate of
buoyancy build up in the later stages.
An assessment must be made of the weight and centre of gravity
position at the time of launch. The procedure then adopted is to move
a profile of the ship progressively down a profile of the launch ways,
taking account of the launching cradle. This cradle is specially
strengthened at the forward end as it is about this point, the so-called
fore poppet, that the ship eventually pivots. At that point the force on the
fore poppet is very large and the stability can be critical. As the ship