4-4.3

product of the associated transverse wind force and its distance from the vessel's

center of gravity. In the local ship coordinate system, this is the moment about the "Z"

axis. Wind yaw moment is determined from the equation:

(8)

EQUATION:

where

wind yaw moment (newton*m)

ρa =

mass density of air (from Table 4-1)

wind speed (m/s)

Vw =

longitudinal projected area of the ship (m2)

Ay =

length of ship (m)

L=

C xyw {θw } = normalized yaw moment coefficient

= moment arm divided by ship length

θw =

wind angle (degrees)

The normalized yaw moment coefficient depends upon the vessel type.

Equation 9 gives equations for computing the value of the yaw moment coefficient and

Table 4-5 gives empirical parameter values for selected vessel types. The normalized

yaw moment variables is found from:

θw * 180

EQUATION: *C*xyw {θw } = - a1 * sin(

0<θw<θz

(9)

)

θz

(9a)

and symmetrical about the longitudinal axis of the vessel,

where

normalized wind yaw moment coefficient

negative peak value (from Table 4-5)

positive peak value (from Table 4-5)

θw =

wind angle (degrees)

θz =

zero moment angle (degrees) (from Table 4-5)

180 * deg

λ =

(dimensionless)

(9b)

[

]

(180 * deg - θz )

79

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