mooring and cable support systenns, are directly influenced by surface forces. 

 Therefore, the sea-air interface must be defined to provide a series of design 

 parameters for the selection of surface hull shapes. Both the average sea state 

 and the worst sea state expected must be considered. 



Winds, gales, and storms depend to a large degree on large, well-defined 

 regions of high and low pressures. In general, the geographic distribution of 

 areas of high and low pressure is fairly systematic and does not vary much 

 between consecutive months. However, there are large seasonal differences 

 in pressure patterns and prevailing winds between summer and winter months. 

 Over the oceans, bad weather consisting of widespread cloudiness, precipitation, 

 high surface winds, and turbulence is essentially a phenomenon associated with 

 rising air currents or low-pressure conditions. High-pressure areas, which are 

 regions of descending air or surface divergence, are generally free from bad 

 weather. Regions which are susceptible to bad weather are the low-pressure 

 zones near the equator and the western and northern portions of the oceans in 

 the northern hemisphere, often referred to as the westerlies or migratory lows. 



Winds, of course, generate waves on the sea surface, with wave heights 

 a function of wind velocity and duration. The worst conditions of sea state 

 and wave forces are described by the Guidance Committee of the Office of 

 Naval Research in its design recommendations as 150-mph winds and 60-foot 

 waves. These conditions were applied as design parameters for surface 

 structures, including mooring and cable support systems, associated with 

 underwater power transmission systems. 



Ocean Currents 



Surface and subsurface ocean currents vary in velocity, according to 

 location, reaching an extreme of approximately 5 knots. The average bottom 

 current velocity, on the other hand, does not exceed 1 knot. Equatorial and 

 warm currents on the western sides of the oceans, such as the Gulf Stream, 

 Kuroshio current. East African current, and East Australian coastal current, 

 have speeds of 2 or 3 knots in general. 



From recorded observations of surface currents, two design conditions 

 were defined for the underwater power transmission systems. The first is a 

 maximum surface current profile of 6 knots which, in a sense, is the result of 

 average storm conditions. The second is a surface current profile of 3 knots, 

 with stronger subsurface currents to a depth of 3,280 feet. Subsurface current 

 velocities below 3,280 feet are generally agreed to be less than 0.35 knot. At 

 depths below 12,000 feet, design currents may be assumed to be effectively 

 zero. 



The design current profiles are shown in Figure 1. These curves may 

 be used with other surface currents of greater or lesser magnitudes by using 

 the same ratio of decay. 



