per minute against a head of 700 psi. A 3-hp, 

 shunt-wound, 120-VDC motor drives the 

 pump. 



The trim tanks, constructed to fit the hull's 

 inside contour, have a total capacity of 356 

 pounds in the forward tanks and 375 pounds 

 in the aft tanks. 



The system is designed for working pres- 

 sure of 700 psi and is protected by the use of 

 a relief valve. A strainer is located at the 

 pump inlet to remove suspended matter from 

 the seawater or the system to protect the 

 pump from damage. 



MBT Differential Fill: 

 Two vehicles, SEA OTTER and BENTHOS 



V, attain trim by differentially filling their 

 MBT's. The system is operationally similar 

 to differential filling of the VBT's as de- 

 scribed above. When partially full the MBT's, 

 which are not pressure-resistant tanks, must 

 be pressure compensated; in the case of SEA 

 OTTER, internal pressurization is accom- 

 plished by high pressure air. 



Shot Hopper Differential Fill: 



Vehicles that include fore and aft iron shot 

 containers for jettisonable ballast have the 

 option of differentially dropping shot to at- 

 tain a variety of up or down bow angles. 

 However, the general operational procedure 

 is to drop shot equally from both hoppers to 

 retain horizontal trim. Only one submersible, 

 the tethered GUPPY, operationally employs 

 its droppable shot to attain trim (11). 



Shot ballast in GUPPY is provided in a 

 single cannister on the fore-and-aft axis of 

 the sphere and forward of the sphere center. 

 Shot can be released from inside the sphere 

 by manipulating the shot valve. The location 

 of the shot ballast is such that by dropping 

 shot, the vessel's trim can be corrected after 

 picking up bottom samples or other material 

 while submerged and carrying them at the 

 forward part of the vehicle. The total capac- 

 ity of shot ballast is 175 pounds. 



Since the single-shot hopper provides the 

 only ballast affecting trim that can be re- 

 leased under water, the vehicle will go down 

 by the stern when shot is released. Trimming 

 or heeling in other directions while sub- 

 merged can only be done by moving weights 

 inside the pressure hull. 



Battery Shift: 



Similar in operation and effect to the inter- 

 nal weight-shift trim system described 

 above, several vehicles employ a trim system 

 composed of movable batteries. The MER- 

 MAID-class vehicle is typical. 



To compensate for changes in weight dis- 

 tribution in the longitudinal direction — 

 which could occur either when equipment is 

 moved or when the operator moves forward 

 from his seat to a lying position — MERMAID 

 is equipped with a battery shifting system. 



When the central hydraulic power supply 

 is working, trimming is affected via the hy- 

 draulic network and is hand controlled. The 

 system permits the longitudinal inclination 

 to be adjusted approximately ±20 degrees. 



The U.S. Navy's MAKAIiAI also employs a 

 battery-shift trim system, but it is used only 

 on the surface to attain gross trim before the 

 dive and cannot be adjusted again until the 

 vehicle surfaces. 



Ballast Weight Drop: 



The submersible DEEP VIEW, in addition 

 to internal movable ballast, has twenty 5- 

 pound steel plates attached to its keel for- 

 ward and aft. By individually dropping a fore 

 or aft weight the vehicle can attain up/down 

 bow angles. Because the application of this 

 system results in an overall loss of negative 

 buoyancy, 16 buoyancy blocks weighing 3 

 pounds each are located atop the hull. They 

 are individually jettisonable and may be re- 

 leased to counteract any undesired gain in 

 positive buoyancy attained through use of 

 the trim system. 



Water Transfer: 



Similar in effect to fore/aft water transfer 

 within the pressure huU, BEAVER's external 

 system consists of three spherical titanium 

 tanks, one mounted aft (1,238-lb capacity) 

 and two mounted port/starboard amidships 

 of 943-pound capacity each (Fig. 6.12). A hy- 

 draulically driven pump transfers water be- 

 tween these tanks at 200 pounds/minute to 

 gain ±27-degree up/down bow angles. This 

 same system can also transfer seawater be- 

 tween the port/starboard tanks to attain list 

 or roll angles of ±12 degrees. 



306 



