Page 202 - Practical Ship Design

168 Chapter 6

displacement and speed from the "basis" and that other factors like propeller revs
are constant, it can give reasonable results.

(ix) Froude and Reynolds' numbers
V
Froude number (F,) = ~ (6.30)
JgL

V
Volumetric Froude number F, = (6.3 1)
-\;n-v"'

v .L
Reynolds number (R,) = __ (6.32)
V
where
L = ship length all in compatible units.
V = displacement volume
V =speed
g = acceleration due to gravity
v = kinematic viscosity = p/r

p = viscosity; r = density
In the units normally used:
v = 1.188 x m2/S for salt water at 15°C
= 1.139 x 1 O4 m2/S for fresh water at 15°C
0.298Vk - 0.164Vk
F, = -
AJL,

where
V, = speed in knots
L, = length in feet
L, = length in metres.
The values of F, in normal use range from about 0.12 to 0.48. For the BSRA
standard 122 m (400 ft) ship these correspond to about 8-32 knots.

0.1 64Vk
F, =-
~(116)
where A = displacement S.W. in tonnes
It can be convenient to express Reynolds' number in terms of the Froude
number