4-4.2

vessel is defined as that component of wind force parallel to the centerline of the vessel.

This is the force in the "X" or surge direction in Figure 4-2. Figure 4-1 shows the

definition of winds areas.

The longitudinal force is determined from NCEL, TN-1628 using the

equation:

Fxw = 0.5 ρa Vw 2A x Cxw fxw (θw )

(5)

EQUATION:

where

longitudinal wind force (newtons)

Fxw =

ρa =

mass density of air (from Table 4-1)

wind speed (m/s)

Vw =

transverse wind area of the ship (m2)

Ax =

longitudinal wind force drag coefficient

Cxw =

fxw (θw ) =

shape function for longitudinal force

θw =

wind angle (degrees)

The longitudinal wind force drag coefficient, *C*xw , depends on specific

characteristics of the vessel. Additionally, the wind force drag coefficient varies

depending on bow ( *C*xwB ) or stern ( *C*xwS ) wind loading. Types of vessels are given in

three classes: hull dominated, normal, and excessive superstructure. Recommended

values of longitudinal wind force drag coefficients are given in Table 4-3.

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