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 TB 55-1900-232-10
G-2.1 FRICTIONAL RESISTANCE . The data used for determining frictional resistance are based upon a
series of experiments on modeled and actual conditions. The resistance caused by the friction of water on the
vessel's wetted surface depends upon.
a. Area of surface below the waterline
b. Nature of the surface
c. Speed of tow.
Thus the formula for frictional resistance of a vessel passing through water is:
R = f1 x Sx(V/6)2 (1)
where:
R = resistance in pounds
S = area of the vessel's wetted surface below the waterline, in square feet (from Table G-4)
V = speed of tow in knots relative to still water.
G-2.2 WAVE-FORMING RESISTANCE.
Data for wave-forming resistance are based on model tests and depend upon:
a. Area below waterline (maximum cross section)
b. Form of bow and stern
c. Speed of tow.
Thus the formula for wave-forming resistance of a body passing through water is'
2
G = 2.85xBxf2xV xK (2)
where:
G = resistance in pounds
B = cross-sectional area of vessel below waterline in square feet (from Table G-4)
V = speed of tow in knots relative to still water
K = 1.2, which is a 20 percent increase in resistance resulting from rough water and eddies
G-2.3 WIND RESISTANCE. Data used for determining wind resistance are based on a series of experiments
on models. The resistance caused by wind blowing against a vessel depends upon:
a Cross-sectional area of vessel above waterline subjected to wind
b. Speed of wind
c. Speed of tow
d. Shape of vessel subjected to wind.
Thus the formula for frictional resistance caused by wind is'
W = C x .004 (Vw + V)2 X f3 (3)
where:
W = resistance in pounds
C = cross-sectional area of vessel above waterline in square feet (from Table G-4)
Vw= speed of wind in knots
G-18
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