Seakeeptng Constderattons tn a Total Destgn Methodology 
Fourth, the Effective Horse Power necessary to overcome the 
mean added resistance in waves as a function of ship speed and sea 
state (H V3) is computed using the appropriate Seakeeping Tables 
from Reference 3. Finally, the Effective Horse Power ofa ship 
operating in a seaway is obtained by adding the bare hull calm water 
EHP (augmented by the appendage allowance) and the EHP necessary 
to overcome the increased resistance due to fouling, the wind resis- 
tance and the mean added resistance in waves. The results of sucha 
computation can be found in Figures 3 and 4, 
Speed Calculations without Motion Considerations 
Given the EHP curves as a function of ship speed and sea state 
it is possible to compute the average ship speed (assuming no limi- 
tations due to motion) for a prespecified engine output, SHP,, in the 
following manner. 
First, a family of propellers is selected. For the present study 
the Wageningen B-Screw Series, see Reference 10, is selected. The 
propeller type used in the present study is the B.4.55 propeller. It 
is of interest to note that ships similar to the ones investigated in 
this study operate using propellers with characteristics similar to 
the B.4.55 propeller. 
Next the curve of Ky /J* is computed and plotted on the pro- 
peller diagram to allow the selection of the most efficient propeller 
for operation in a prespecified sea state. In the present ae it was 
decided to optimize for the sea state characterized by H 13= 7, 94 ft. 
because according to information given in Table 1 it is the sea state 
that occurs most frequently. In the computation of 
eae EHP * 325. 66 
i p* abc ys (1. 6889)>* (ithe) “ee (1-t) 
the ae and ship speed V was determined from the EHP vs V 
and H'3 curves developed in the previous section, the propeller dia- 
meter d was takenasin Reference 4 , i.e. d 20.70 T, and the 
values for w and t were determined from Reference 4 from the 
calm water data, These values were assumed to apply to the propel- 
ler operating in the seaway. Unfortunately the effect of this assump- 
tion cannot be estimated as very little is published on the subject. 
However the results obtained from the calculations using this assump- 
tion appear to be in agreement with published results and it is there- 
RAZZ 
