Seakeeping Constderattons tn a Total Destgn Methodology 
where 
F, is the frequency of occurrence of the ith sea state (H 1/3, 
obtained from Table 1. 
V. is the ship speed in the ith sea state (no motion considera- 
tions) 
and N _ is the number of sea states (H 1/3) used to describe the 
environment (N = 6 for this study). 
The results of such a computation can be found in Figures 5 and 6. 
At this stage it is important to point out that in the present 
study SHP, is an independent variable because the calculations are 
not done for an assumed average condition, as was the case with 
Reference 5, but rather for the actual operating environment. 
Speed Calculations with Motion Considerations 
: : nS ; 
The ship speed as a function of sea state (H / ) determined 
from the previous analysis must now be modified to account for pos- 
sible further reductions due to motion considerations. 
The criteria used to determine whether a given ship is motion 
limited or not are the following 
a) For the safety of the crew the RMS vertical acceleration 
at station 15 is not to exceed the value of 0.125 g. This value 
is determined from Reference 11. 
b) For the safety of the cargo 
(i) the average 1/10 highest values of vertical acceleration 
must not exceed one g anywhere along the ship's length. 
From Reference 12 
V 2 
= 1.800 8m__(1- €° 72) 
1 
= /10 “ 
where Vm, is the RMS of the response of interest 
1599 
