Page 97 - Introduction to Naval Architecture

5 The environment

Apart from submerged submarines, ships operate on the interface
between air and water. The properties of both fluids are important.

BASIC PROPERTIES

Water
Water is effectively incompressible so its density does not vary with
depth as such. Density of water does vary with temperature and salinity
as does its kinematic viscosity. The density of sea water increases with
increasing salinity. The figures in Table 5.1 are based on a standard
salinity of 3.5 per cent.

Table 5.1 Water properties

Kinematicc viscosity
Density
Temperature
Temperature Der,isity Kinematic viscosity
3 3
TO (kg/m ) ) (mVs X 10 ) ' '
6 6
)
10
x
•m
(mVs
(°C)
(kg/
Fresh water water
Fresh Salt water water Fresh water Salt water
Fresh water
Salt water
Salt
0 999.8 1028.0 1.787 1.828
10 999.6 1026.9 1.306 1.354
20 998.1 1024.7 1.004 1,054
30 995.6 1021.7 0.801 0.849
The naval architect has traditionally used approximate figures in
calculations. These have included taking a mass density of fresh
3
water as 62.21b/ft (36 cubic feet per ton) and of sea water as 64 lb/
3
ft (35cubic feet per ton). The corresponding 'preferred' values in
3
SI units are l.OOOtonne/m and 1.025 tonne/m respectively.
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