Page 284 - Practical Ship Design

242 Chapter 8

3
Forward

2
LCB as
%L from
amidships
B.P.
1

Amidships

I

2

Aft
3
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85
Block Coefficient

Fig. 8.8. LCB position v. blockcoefficient. Graph shows the range of LCB positions within which it is
possible to produce lines with resistance close to optimum. Assumes F,-C, relationship of Watson-
Gilfillan mean line.

towards drawing a sectional area curve is the determination of what its maximum
ordinate, the midship area coefficient (C,) should be.
A formula for C, in terms of the bilge radius and rise of floor is:
F[(B / 2 -K / 2) - R2 / (B / 2 -K / 2)] + 2R2( 1 - n / 4)
c, =1- (8.1)
BxT

where
F = rise of floor
K = width of keel
With no rise of floor this reduces to:

2R (1 - n / 4)
c, =l-
BxT
Both of these formulae can be transposed to give formulae for R if C, is known.