chapter 20 

 STAGING VESSEL MOORING COMPLEX 



T. N. Blockwick 

 Boston Naval Shipyard 

 Boston, Massachusetts 



INTRODUCTION 



The site of Sealab II was about 4000 ft offshore at La Jo 11a, California, and almost directly 

 west of Scripps Pier. This location made all surface sea operations vulnerable to weather and 

 seas from the prevailing western direction. Although bad weather was not expected during Au- 

 gust, September, and October, the possibility could not be discounted. 



The two most important open-sea operations of Sealab II were the precision mooring and 

 positioning of the surface -support craft and the handling of the Sealab n habitat and the per- 

 sonnel transfer capsule (PTC). 



The Sealab habitat is basically a cylindrical unpowered small submarine of about 200 tons 

 displacement. The surface -support craft, called the staging vessel or the Berkone, is essen- 

 tially two YFN barges joined together. It is 90 ft wide and 110 ft long. 



The mooring aspect of Sealab II was particularly important, for tv/o reasons. First, the 

 moor would have to be extremely reliable. Failure of the moor would endanger the lives of the 

 subjects in the habitat, although they could be independent of the surface -support craft for a 

 limited period of time. Secondly, in order for the surface -support craft to perform its function 

 effectively, it was necessary for it to remain within a ten-foot circle, so that equipment could 

 be lowered in a precise location (Fig. 73). The positioning of the personnel transfer capsule 

 (PTC) near the Sealab II habitat was particularly critical, since aside from its primary function 

 of transporting divers under bottom pressure to the deck decompression chamber (DDC), it 

 was also an emergency haven for the Sealab divers in the event of an emergency, such as at- 

 mosphere contamination, fire, flooding, etc. Further, the ocean bottom in the vicinity was ex- 

 tremely uneven and fast changing, with slopes of 45 degrees not uncommon. Equipment could 

 not be landed in such terrain, and suitable flat areas had to be pinpointed. The site was near 

 the Scripps Canyon, which drops precipitously to a depth of 700 ft. 



To provide for safety in bad weather and precise mobility, a five-leg moor (Fig. 74) was 

 designed. Three of the legs were located in the sector of maximum expected weather which 

 was from the west. Two of the legs (Nos. 1 and 5) were unique, in that they had to span the 

 Scripps Canyon (Fig. 75). 



Each leg was designed to resist a 50-knot wind on the surface -support vessel. This would 

 require that each leg be capable of resisting a 50,000-lb pull. To determine the holding power 

 of the soil in the area, several anchor tests were made under controlled conditions and a two- 

 to-one scope. The holding-power-to-weight ratio was found to be at least seven to one and was 

 considered satisfactory. 



The basic leg consisted of the following: 



1. A 13,000-lb Navy Stockless Anchor with a 1-1/4-in. crown wire of length equal to the 

 water depth plus 30 ft connected to a 59-in. spherical buoy of 3000-lb buoyancy. 



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