Trim and Ballasting 



The metacentric height is usually so low on 

 submersibles that even a small instrument 

 mounted in the wrong location may cause a 

 significant change in trim characteristics. In 

 the same vein, a protruding instrument may 

 change the hydrodynamics or "flight" char- 

 acteristics of a vehicle and, consequently, its 

 control underway. Thus, weight and balance 

 calculations must precede attachment. A 

 payload of several hundred pounds does not 

 necessarily mean that the entire payload 

 capability can be used at one location on the 

 vehicle, but instead, it may have to be dis- 

 tributed equally throughout. 



Corrosion and Fouling 



The great majority of submersibles are 

 brought aboard ship following each dive and 

 washed down with fresh water. Conse- 

 quently seawater corrosion and fouling by 

 marine organisms is usually not a problem. 

 The large, towed vehicles, however, are sub- 

 ject to both problems. Corrosion of instru- 

 ments has not been sevei-e because very few 

 of the large submersibles have operated un- 

 der a contract for sufficient continuous pe- 

 riods of time to encounter a serious corrosion 

 problem. Fouling, on the other hand, was a 

 problem during BEN FRANKLIN's pre-Gulf- 

 stream drift testing period. BEN FRANK- 

 LIN's mooring was in an area of considerable 

 water circulation where goose-neck (Bala- 

 noid) barnacles attached to the vehicle and 

 its equipment. In a 3-week period, the barna- 

 cles (2-3 mm across) colonized the protective 

 glass covering over the camera lenses, the 

 strobe light bulbs and transducer heads to a 

 density of 80-100 individuals per square inch 

 (Fig. 11.1). This was cause for concern as the 

 vehicle was scheduled for a 30-day submer- 

 gence and such a colonization/growth rate 

 could be detrimental to the mission. Investi- 

 gation into available anti-fouling methods 

 revealed no positive deterrent; consequently, 

 no protective measures were taken. At the 

 end of the 30-day submergence, careful in- 

 spection revealed no fouling organisms pres- 

 ent; it was deduced that BEN FRANKLIN, 

 drifting at a rate equal to the current, was 

 unsuitable as a home for organisms depend- 

 ent upon water moving past them to supply 

 food and remove waste products. 



Hg 1 1 1 Bamacle-encrjsted transducer after 3 weeks ir> Port ot West Palm Beacti, 

 Fla, (NAVOCEANO) 



Pressure (Depth) 



While it may appear obvious to be certain 

 that an instrument can sustain the maxi- 

 mum pressures anticipated on a dive without 

 leaking or imploding, there is a safety factor 

 which should be included in their design. For 

 example, in 1965 the PC-3B was conducting 

 a 600-foot cable survey dive in the Bahamas, 

 and it had an externally-mounted acoustic 

 pinger for surface tracking. The pinger was 

 advertised for a 600-foot depth capability, 

 which was absolutely true, for at 610 feet 

 there was a cannon-like bang produced by 

 the imploding pinger. A safety factor in in- 

 struments at least equal to that of the sub- 

 mersible should be included, not only to as- 

 sure use of the instrument but also to avoid 

 the possibility of creating an implosion 

 Shockwave that might be sufficient to crack 

 a viewport. 



Negative Buoyancy 



Several ocean bottom instruments (corers, 

 sound velocity probes, bearing strength 

 probes, etc.) and engineering tools 



540 



