Page 204 - Introduction to Naval Architecture

190 RESISTANCE

(3) scaling the model residuary resistance to the full scale by
multiplying by the ratio of the ship to model displacements;
(4) adding a frictional resistance for the ship calculated on the basis
of the resistance of a flat plate of equivalent surface area and
roughness;
(5) calculating, or measuring separately, the resistance of
appendages;
(6) making an allowance, if necessary, for air resistance.

ITTC method
2
The resistance coefficient is taken as C- (Resistance) /\p 5V . Subscripts
t, v, r and f for the total, viscous, residual and frictional resistance
components. Using subscripts m and s for the model and ship, the
following relationships are assumed:

where k is a form factor.

where dCf is a roughness allowance.

The values of Q are obtained from the ITXC model-ship correlation
line for the appropriate Reynolds' number. That is, as in Table 8.3:

k is determined from model tests at low speed and assumed to be
independent of speed and scale.
The roughness allowance is calculated from:

6
where ^ is the roughness of hull, i.e., 150 X 10 m and L is the length
on the waterline.
The contribution of air resistance to C^ is taken as 0.001 A T/S where
A T is the transverse projected area of the ship above water.