Chryssostomidts 
fore concluded that this assumption is not unrealistic. 
Once the open water efficiency © is computed the propulsive 
efficiency 1p, is then calculated 
IZ O H R iS) 
where ike = (1-t) / (1-w) 
1 = relative rotative efficiency 
(Reference 9 suggests a value of 1.026 which 
was adopted for all sea states) 
uP = shaft transmission efficiency 
(Reference 9 suggests a value of 0.98 for 
machinery aft, which was adopted in the pre- 
sent study) 
This allows to compute, SHP,, the power required to operate 
a given ship at a given speed and sea state from the following equation 
SHP_ = EHP / 1p: 
The above calculations are repeated by selecting pairs of values for 
EHP@and? V until SHE 7 — sHP, - 
This procedure is then repeated using pairs of EHP and V 
values from the EHP curves corresponding to the other sea states of 
interest. In these calculations of course the propeller selected for the 
sea state characterized by H'3 = 7. 94 ft. is always used. Once the 
speed that can be achieved in all the sea states of interest for a given 
SHP, , the average speed, Vg, , can be obtained from the following 
equation 
1598 
