3.4.1
The measured drag coefficient
(CD
), lift coefficient (CL
)
and heeling moment coefficient (CM
) are shown
in figure 3.4. They are non-dimensionalized
by the following equations:
3.4.2
In the figure the angle of
heel is defined as positive when the ship heels to lee side (refer
to figure 3.1). The broken
line is the heeling moment coefficient of the standard weather criterion,
calculated from equation (N-3.5), which is derived from the equation
in paragraph 3.2.2.2 of the Code. However, in order to be compared
with the test results, Z is replaced by the height of
the centre of the lateral projected area above waterline, i.e. Hc in
table 2.1.
Measured drag coefficient (CD
),
lift coefficient (CL
) and heeling moment coefficient
(CM
)
3.4.3
It is characteristic in the
figure that all the quantities (CD
, CL
and CM
) vary significantly with
heel angle. As for the heeling moment, it is smaller than the standard
criterion and further reduces when the ship heels, especially to lee
side. The lift force is not so small and close to the drag force when
the heeling angle is -5° (weather side). However, the adjustment
of the vertical position of the model is not necessary since the lift
force is 0.7% of the displacement of the ship in a wind speed of 26
m/s.
3.4.4
For comparing the test results
with Z in equation (N-3.5), the measured heeling moment
was converted to the height of the centre of wind force above waterline, lwind
, by the following equation:
3.4.5
The result is shown in figure 3.5. It can be observed that
the centre of wind force is also a function of heel angle.
Height of the centre of wind force above waterline (model scale)