SECT. 5] DEEP-SEA ANCHORING AND MOORING 521 



mooring must survive for long periods of time, the mooring may have to be 

 designed with no surface float. 



Where sea-ice is present it is not possible to employ moorings with surface 

 floats. Ice build-up on the float may occur in sleet or black-ice storms at high 

 latitudes. If these factors are hazards, the float should be designed to survive 

 capsizement. 



Near rocky coasts, seals and sea-lions are sometimes troublesome in that they 

 leap aboard and bask on any large enough surface float. They may break 

 antennae or even capsize the float. They can be discouraged by designing the 

 float without flat horizontal surfaces. 



On the bottom in the deep ocean, there are a number of sharp objects, debris 

 that has been jettisoned, wrecks, rock outcroppings and nodules. In general, 

 therefore, any part of the mooring cable that is allowed to touch and drag on 

 the bottom must be high quality flexible wire rope several times stronger than 

 the main mooring cable. 



Perhaps the most difficult problem stems from human intervention. If the 

 surface floats on a mooring are conspicuous, visually or by radar, passing craft 

 will pull off course to investigate. If there are any floating lines about the float 

 they are very likely to be picked up on the hull or in the screws. In addition, 

 fishermen will tie up to the moorings, attempt to hoist them, or cut them free. 

 In many cases this recovery is intended to be helpful. Regardless of the warnings 

 or information painted on the float, seamen cannot believe that a float in 2000 

 or 3000 fm is moored there. 



The importance of these environmental factors can perhaps be indicated by 

 the fact that of those fifteen or so moorings that have been recovered off 

 stations by Scripps Institution, only about two appeared to have failed from 

 direct natural stress. All others showed evidence of having been fouled by 

 ships, cut free by fishermen, or in several cases bitten off by sharks. A broken 

 shark tooth was recovered embedded in one parted pennant. 



4. Remarks on Components of Moorings 



The components will next be discussed followed by general design problems. 



A. Surface Floats 



The translocation of horizontal forces on and near an oscillating surface to 

 the bottom cannot be carried out simply, and many restrictions to the manner 

 in which it is carried out are determined by the type of surface float. 



Two general types of surface float are feasible : ( 1 ) a surface-following or 

 responding float ; that is, a float such as a skiff or nun-buoy that tends to move 

 with the waves, and (2) a vertically stable float, such as a spar or "hydrometer- 

 shaped" float that tends to remain in a vertical plane even in the presence of 

 waves. 



Each of these types of surface float has its specific advantages and dis- 

 advantages. For the purpose of this discussion, however, the difficulty with the 



