Page 92 - Introduction to Naval Architecture

FLOTATION AND STABILITY 79

trapezia. The body effectively becomes a rectangular vessel 60 m
long (but with buoyancy only over the aftermost 52 m) by 10 m wide
with an LCG 30 m from one end and the LCB 26 m from aft. It will
trim by the bow until the LCB is 30 m from aft. It will be found that
the draught aft = 1.863 m and the draught 52 m forward of the after
end - 5.059 m. The draught right forward will be:

Stability in the damaged condition
Consider first the lost buoyancy method and the metacentric height
The effect of the loss of buoyancy in the damaged compartment is to
remove buoyancy (volume v) from a position below the original
waterline to some position above this waterline so that the centre of
buoyancy will rise. If the vertical distance between the centroids of
the lost and gained buoyancy is bfy the rise in centre of buoyancy =
juvhbi/ V. JSMwill decrease because of the loss of waterplane inertia
in way of the damage. If the damaged inertia is I d, BM^ = /d/V. The
value of KG remains unchanged so that the damaged GM, which may
be more, but is generally less, than the intact GM is:

If the added weight method is used then the value of KG will change
and the height of M can be found from the hydrostatics for the intact
ship at the increased draught. The free surface of the water in the
damaged compartment must be allowed for.

Asymmetrical flooding

When there are longitudinal bulkheads in the ship there is the
possibility of the flooding not extending right across the ship causing
the ship to heel. In deciding whether a longitudinal bulkhead will be
breached it is usually assumed that damage does not penetrate more
than 20 per cent of the breadth of the ship. Taking the case
illustrated in Figure 4.35 and using the added weight approach, the
ship will heel until:

VGM