UFC 4-159-03
3 October 2005
Table 4-1. (continued) Engineering Properties of Air and Water
Air at Sea Level at 20oC (68oF)*
PROPERTY
SI SYSTEM
ENGLISH OR
INCH-POUND
SYSTEM
1.221 kg/m3
0.00237 slug/ft3
Mass density, ρa
11.978 newton/m3
0.07625 lbf/ft3
Weight density, γa
1.50E-5 m2/sec
1.615E-4 ft2/sec
Kinematic viscosity, ν
*
Note that humidity and even heavy rain has relatively
little effect on the engineering properties of air (personal communication with the
National Weather Service, 1996)
4-3
PRINCIPAL COORDINATE DIRECTIONS. There are three primary axes
for a ship:
X - Direction parallel with the ships
Longitudinal axis
Y - Direction perpendicular to a vertical plane
through the ship's longitudinal axis
Z - Direction perpendicular to a plane formed by
the "X" and "Y" axes
There are six principal coordinate directions for a ship:
Surge - In the "X"-direction
Sway - In the "Y"-direction
Heave - In the "Z"-direction
Roll - Angular about the "X"-axis
Pitch - Angular about the "Y"-axis
Yaw - Angular about the "Z"-axis
Of primary interest are: (1) forces in the surge and sway directions in the
"X-Y" plane, and (2) moment in the yaw direction about the "Z"-axis. Ship motions occur
about the center of gravity of the ship.
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