4.3.3.1 Symbols
H  :  Significant wave
height 
T:  :  Mean wave period 
V  :  Ship speed 
 :  Angle between ship course and regular
waves (angle 0(deg.) is defined as the head waves
direction) 
_{}  :  Mean wave direction 
_{}  :  Amplitude of incident regular
waves 
_{}  :  Circular frequency of incident regular
waves 
4.3.3.2
Irregular waves can be represented as linear
superposition of the components of regular waves.
Therefore added resistance due to waves R_{wave} is also calculated by
linear superposition of the directional spectrum
(E) and added resistance in regular waves
(R_{wave}).
4.3.3.3 Added resistance in
irregular waves R_{wave }should be
determined by tank tests or a formula equivalent in
terms of accuracy. In cases of applying the theoretical
formula, added resistance in regular waves
R_{wave} is calculated from the
components of added resistance primary induced by ship
motion in regular waves, R_{wm} and
added resistance due to wave reflection in regular waves
R_{wr} as an example.
R_{wave} = R_{wm} +
R_{wr}
As an example, R_{wm} and
R_{wr} are calculated by the
method in 4.3.3.4 and 4.3.3.5.
4.3.3.4
Added resistance primary induced by ship motion in
regular waves
(1)  Symbols 
  :  Gravitational
acceleration

 H(m)  :  Function to be determined by the
distribution of singularities which represent
periodical disturbance by the
ship 
 V  :  Ship speed 
  :  Angle between ship course and regular
waves (angle 0(deg.) is defined as the head waves
direction) 
  :  Fluid density 
  :  Circular frequency of incident regular
waves 
(2)  Added
resistance primary induced by ship motion in
regular waves R_{wm} is
calculated as follows: 
 
4.3.3.5 Added resistance due
to wave reflection in regular waves
(1)  Symbols 
 B  :  Ship
breadth 
 B_{f}  :  Bluntness coefficient, which is
derived from the shape of water plane and wave
direction 
 C_{u}  :  Coefficient of advance speed, which is
determined on the basis of the guidance for tank
tests 
 d  :  Ship draft 
  :  Froude number (nondimensional number
in relation to ship speed) 
  :  Gravitational acceleration 
 I_{1}  :  Modified Bessel function of the first kind of
order 1 
 K  :  Wave number of regular
waves 
 K_{1}  :  Modified Bessel function of the second
kind of order 1 
 L_{pp}  :  Ship length between
perpendiculars 
 V  :  Ship speed 
  :  Angle between ship course and regular waves
(angle 0(deg.) is defined as the head waves
direction) 
 _{d}  :  Effect of draft and
frequency 
  :  Fluid density 
  :  Amplitude of incident regular
waves 
  :  Circular frequency of incident regular
waves 
(2)  Added
resistance due to wave reflection in regular waves
is calculated as follows: 
 Figure 4.1: Coordinate system for wave
reflection 
(3)  Effect of advance speed _{u }is determined as
follows: 
 
(4)  The
coefficient of advance speed in oblique waves is
calculated as follows: 
 
(5) The aforementioned
coefficient _{} is determined by tank tests.
The tank tests should be carried out in short waves
since R_{wr} mainly works in short
waves. The length of short waves should be 0.5
L_{pp} or less.
(6) Effect of advance speed in regular head
waves _{U} is calculated by the
following equation where _{} is added resistance obtained by the tank
tests in regular head waves, and R_{wm}
is added resistance due to ship motion in regular waves
calculated by 4.3.3.4.
(7) Effect of advance speed _{U} is obtained for each speed
of the experiment by the aforementioned equation.
Thereafter the coefficient of advance speed _{} is determined by the least square method
against F_{n}; see figure below. The
tank tests should be conducted under at least three
different points of F_{n}. The range
of F_{n} should include the
F_{n }corresponding to the speed
in a representative sea condition.
Figure 4.2: Determination of the
coefficient of advance
speed