124 



SUPPORT VESSEL 



Fig. 65. Pressure pot for transferring dry items and 

 cage for transferring wet itenns are lifted aboard the 

 surface support vessel 



LOWERING COUNTERWEIGHT SYSTEM 



In order to safely lower and raise the Sealab between the staging vessel and the bottom, it 

 was necessary to make some provision for allowing for the relative motion between it and the 

 vessel. It was anticipated that a majdmum relative motion due to wave action, of about 10 ft, 

 would be possible during a wave half -period of about 5 sec. Accordingly, a counterweighted 

 system, as shown in Fig. 66, was used for lowering and raising both the Sealab and the PTC. 

 This system had the effect of maintaining a nearly constant tension on the lowering line during 

 the lowering and raising operations. Had this system not been used, the tension in the line 

 would fluctuate between zero (free fall of the object through the water) to a value so high as 

 would likely part the line or cause other failure of the weakest element. 



Characteristics of the counterweight system as used for the Sealab n Project are shown 

 in Fig. 67. 



When operated properly, the system had the very desirable characteristics of smoothly and 

 automatically loading and unloading itself when the bottom or surface is reached. The system 

 could handle a wide range of loads without changing the size of the counterweight. There are 

 theoretically no points of discontinuity, or conditions that would produce shock loads on the 

 line, between the load range of zero to infinity. This was not strictly true in actuality, of 

 course, since at low loads, fluctuating between and 500 lb at the staging vessel's natural pitch 

 period, the counterweight's response would not match the vessel's motion due to its own inertia. 



Operation in this load range (0 to 500 lb) was required on occasions to keep a slight tension 

 on the line when the PTC was sitting on the bottom prior to liftoff. This condition was met by 

 placing a small auxiliary counterweight directly on the lowering line (allowing it to hang in the 



