CABGO AND TRIM 523

Change of mean draught= =— =1-89 inches

T r I. 53

m x i A • total moment 150x100 ^K . ,
Total tnm= ITM-----=___ =10-5 inches

Half the total trim is allocated to each end of the ship so that she
will go down 5J ins. forward and rise 5J ins. aft and increase her mean
draught 1-89 inches.

A rough approximation of the ITM. may be found when one has a
ship to experiment with by noting very carefully the ship's draught,
then running up a double bottom tank, and again carefully noting the
new draught. The weight of water in the tank can be got from tne
ship's displacement scale and the distance of its centre of gravity from
the tipping centre measured from the profile plan.

Fig. 42.

Example.—The centre of gravity of No. 6 D.B. tank is 150 feet
abaft the tipping centre and contains 221 tons water.

ft. ins. ft. ins.

Draught before fining 12 06 F 12 06 A

Draught after filling 11 06 13 06

— 1 00 + 1 00
The total alteration of trim is therefore 24 inches.
, . total moment 150 ft. X 221 tons
Total trim • ^^ or, 24 ins. =-------__-------
LTM. = 150 X 221-r-24=1381 foot-tons.
, The I.T.M.=1381 foot-tons, a. quantity which would yield, theoreti-
cally, answers approximately correct for that particular draught.
Example,—The draught of a ship on arrival at a port of call will be
22 ft. 01 ins. forward, 24 ft. 10 ins. aft, when cargo will be discharged
as follows: T.P.I. 53 tons; I.T.M. 1423 foot-tons, what will her draught
be then ?