UFC 4-159-03
3 October 2005
Values of f xw (θw ) are symmetrical about the longitudinal axis of the vessel. So when
θ w > 1 8 0 , use 3 6 0 - θ w as θ w in determining the shape function. Note that the
maximum longitudinal wind force for these vessels occurs for wind directions slightly off
the ship's longitudinal axis.
EXAMPLE: Find the longitudinal wind drag coefficient for a wind angle of 40 degrees
for the destroyer shown in Figure 4-5.
SOLUTION: For this destroyer, the following values are selected:
θx = 70o from Table 4-4
CxwB = 0.70 from Table 4-3
CxwS = 0.80 from Table 4-3
This ship has a distributed superstructure and the wind angle is less than the crossing
value, so Equation 7a is used to determine the shape function:
= (90o / (70o ))40o + 90o = 141.4o
γ
-
sin (5 * 1 4 1.4 o )
sin (1 4 1.4 ) -
o
10
f xw (θ w ) =
= 0.7 2
0 .9
At the wind angle of 40 degrees, the wind has a longitudinal component on the stern.
Therefore, the wind longitudinal drag coefficient for this example is:
Cxw fxw (θw ) = 0.8 * 0.72 = 0.57
78
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