tion of 600 pounds to a light condition of 600 

 pounds. A float switch was included to open 

 the electric motor circuit when the working 

 fluid was exhausted from the spheres. A 

 pressure transducer sensed absolute pres- 

 sure in the spheres. The readout from this 

 pressure was calibrated to show the quantity 

 of oil in the spheres. Relief valves were in- 

 cluded to protect the pump motor in case of 

 valve failure and a filter was provided to 

 capture any stray particles in the fluid. Fluid 

 was filtered whenever it was allowed to flow 

 back into the sphere. A check valve system 

 was employed to bypass the filter in the 

 reverse direction. 



DEEPSTAR 4000 used its variable dis- 

 placement system in a somewhat different 

 fashion than the designers intended when 

 the need for more rapid buoyancy changes 

 arose. In conjunction with its small weight 

 drop system (described below) the system 

 worked as follows: At neutral buoyancy, the 

 flexible bag was full; if positive buoyancy 

 was needed, a 3.4-pound weight was dropped; 

 if negative buoyancy was necessary, fluid 

 was pumped from the flexible bag. Hence, a 

 round trip from negative-to-positive-to-nega- 

 tive was reduced by half that required if the 

 total variable displacement system was em- 

 ployed. 



Ascent/Descent Weights: 



Funciion: To assist the submersible in de- 

 scending and ascending to and from the bot- 

 tom while conserving electrical power. 



Operation: Generally one weight is hung fore 

 and another aft; both are attached prior to 

 launching. When the MBT's and VBT's are 

 full, the vehicle descends to some depth short 

 of the bottom, and the descent weight is 

 dropped to give the vehicle approximate neu- 

 tral buoyancy. At dive termination, the as- 

 cent weight is dropped allowing the vehicle 

 to surface. On some vehicles, e.g., ALVIN, a 

 descent weight only is used to hasten the 

 initial descent and, at the same time, con- 

 serve electrical power which might otherwise 

 be required to run the vertical thrusters 

 during descent. 



Location on Vehicle: On the French vehicles 

 SP-350 and SP-3000 and on DS-4000, the 

 descent weight is on the stern centerline and 

 the ascent is forward on the brow. 



Configuration: Any Compatible to the vehicle. 

 Material: Lead or cast iron. 

 Example: 



(a) DEEPSTAR 4000 dives with 220- 

 pound cast iron descent weight aft which 

 causes the vehicle to descend bow high. At 

 some predetermined depth, the descent 

 weight is hydraulically jettisoned, and the 

 vehicle comes to the near-horizontal posi- 

 tion. At dive termination, a 187-pound ascent 

 weight mounted forward is dropped, and 

 DEEPSTAR 4000 ascends (Fig. 6.5). A nega- 

 tive feature of this system lies in the fact 

 that once the ascent weight is dropped, the 

 vehicle cannot descend again without addi- 

 tional negative buoyancy. In the event of the 

 submersible ascending into an overhanging 

 cliff or obstruction, it would be unable to 

 descend again without external assistance. 



(b) DEEPSTAR 4000's sister submers- 

 ible DS-2000 combines both a descent weight 

 and a hard tank. The descent weight per- 

 forms the same function as in DS-4000, but 

 instead of an ascent weight, a 120-pound- 

 capacity tank (which is flooded at the start of 

 the dive) has been substituted. When the 

 dive is terminated, the seawater is blown 

 from the hard tank and the vehicle rises. 

 This allows an increase of 120 pounds in 

 payload owing to the absence of the ascent 

 weight. 



Anchor: 



Function: To provide static stability while 

 working on the bottom or hovering. It also 

 may serve as a kedge to assist in pulling 

 large devices on the bottom. 



Operation: A hydraulically driven winch, ca- 

 ble, and anchor can be employed by the 

 operator as desired. 

 Example: 



Two submersibles routinely carrying 

 anchoring devices are BEAVER and NEMO. 

 While both vehicles are quite different, their 

 anchoring systems are essentially similar. 

 Hence, NEMO will serve as an example of 

 both and its description is taken from refer- 

 ence (6). 



NEMO^s primary vertical mobility and 

 station-keeping modes are provided by the 

 winch/motor system housed in the main bal- 

 last tank. The winch drive motor is a Vickers 

 fixed-displacement, reversible hydraulic mo- 



294 



