Page 98 - Introduction to Naval Architecture

THE ENVIRONMENT 85

Air
At standard barometric pressure and temperature, with 70 per cent
3
humidity air has been taken as having a mass of 0.081b/ft (13 cubic
3
feet per Ib). The corresponding preferred SI figure is 1.28kg/m .
Temperatures
The ambient temperatures of sea and air a ship is likely to meet in
service determine the amount of air conditioning and insulation to
be provided besides affecting the power produced by machinery.
Extreme air temperatures of 52°C in the tropics in harbour and 38°C
at sea, have been recorded: also -40°C in the Arctic in harbour and
-30°C at sea. Less extreme values are taken for design purposes and
typical design figures for warships, in degrees Celsius, are as in Table
5.2.

Table 5.2 Design temperatures

Area of world Average max. suinmer Average min. winter
ttemperature temperature
AiIr Sea Air Sea

DB WB DB WB

Extreme tropic 34.5 30 33
Tropics 31 27 30
Temperate 30 24 29
Temperate winter -4 2
Sub Arctic winter -10 1
Arctic/ Antarctic winter -29 —2

Notes I. Temperatures in degrees Celsius.
2. Water temperatures measured near the surface in deep water.

WIND

Unfortunately for the ship designer and operator the air and the sea
are seldom still. Strong winds can add to the resistance a ship
experiences and make manoeuvring difficult. Beam winds will make a
ship heel and winds create waves. The wave characteristics depend
upon the wind's strength, the time for which it acts, its duration and the
distance over which it acts, its fetch. The term sea is applied to waves
generated locally by a wind. When waves have travelled out of the