Page 351 - Practical Ship Design

308 Chapter 11

TF bears the same relationship to T, as F does to S. All of the above are in mm.
Td = Summer draft in metres
A = displacement in tonnes
Tpc = tonnes per centimetre
The subsidiary timber freeboards have the preface L. The calculation of LT, and
LF, are as above. LWNA remains as WNA and LW is calculated from:
LTd
LW = LS + -
36
LTd is summer timber draft in metres.

11.2.3 Freeboard calculations

The calculation of freeboard is not a difficult matter and most naval architects will
have access to a computer program which will perform this task for them very
quickly. The treatment that follows is neither completely accurate nor filly compre-
hensive, but as the approximations involved result in a very small error, it can be
used with confidence in preliminary design work when no other reference books
are available.
The calculation of a summer freeboard starts with a tabular freeboard read from
the rules in which this is tabulated against ship length. In the rules values are
quoted for every metre from 24 to 365 m. Linear interpolation from the very
abbreviated table given below remarkably introduces a maximum error of less than
25 mm and suggests the rules might have been simplified!

Length of ship Type A Type B
(m> (mm> (mm>
24 200 200
50 443 443
76 786 816
100 1135 1271
150 1968 2315
200 2612 3264
250 3012 4018
300 3262 4630
350 3406 5160
365 3433 5303