Hatch Diameter 



Ranging from 15.75 to 30 inches in diame- 

 ter in different submersibles, the user must 

 be certain that his instrument will physically 

 fit inside the pressure hull. In some in- 

 stances the outside diameter of the hatch 

 can be several inches greater than the inside 

 diameter, the latter, of course, being the 

 controlling dimension. ALUMINAUT pre- 

 sents a unique problem in that its pressure 

 hull hatch is 19 inches in diameter, but its 

 sail hatch is only 17.75 inches. Submersibles 

 with plastic bow viewing domes offer more 

 flexibility because the dome can be removed 

 for installation of devices larger than the 

 hatch. 



Internal Location 



Instruments must be positioned to avoid 

 interference with operational controls, crew- 

 safety and comfort, access to junction boxes 

 and fuses, viewing and access to emergency 

 breathing or escape devices. If more than 

 one instrument is to be visually monitored, 

 they should be grouped closely together to 

 conserve movement. In the cramped confines 

 of the smaller submersibles it may be diffi- 

 cult to meet these requirements if several 

 instruments are desired. 



Electrical Interference 



Submersible electrical power cables are, 

 for the most part, unshielded (3). Therefore, 

 to prevent the vehicle's electronics from in- 

 terfering with scientific instruments the lat- 

 ter's cables should be shielded and physical 

 separation of thru-hull penetrators for both 

 should be sought. Shortest possible cable 

 runs assist in further minimizing interfer- 

 ence. 



Electrical Power 



Submersible-supplied electrical power is 

 characterized by surges and spikes; there- 

 fore, voltage regulators for each instrument 

 are desirable. It is not uncommon for DC 

 voltages to drop about 20 percent during a 

 long duration dive (4). 



Internal Atmosphere 



The atmosphere in a submersible is char- 

 acterized by extremes which may be detri- 

 mental to electronics. In the tropics and sub- 



tropics, high temperatures and high humid- 

 ity prevail on the surface and at shallow 

 depths; condensation with drippage charac- 

 teristically occurs with greater, colder 

 depths. Electrical power is usually too lim- 

 ited for an air conditioning system or the 

 like. Light levels within the pressure hull are 

 low and digital read-outs or dials should be 

 lighted or luminous. 



Connectors/Penetrators 



There is no standard electrical connector 

 or penetrator; therefore, a complete change 

 of instrument terminations may be required. 

 The reliability of underwater connectors still 

 leaves a great deal to be desired. 



Entanglement 



Where instruments are external to the 

 submersible's fairings, they must be de- 

 signed to minimize entanglement with cables 

 or ropes or other protruberances. In the 

 event that such entanglement is a possibil- 

 ity, provisions should be made to jettison the 

 instrument. 



\^ ave Slap 



Under-tow instruments can be torn loose 

 or severely damaged by wave slap and 

 should be either designed to withstand 1,000 

 psi or located to neutralize its effects — pref- 

 erably both. 



Unhindered Data 



Placing an instrument within the vehicle's 

 fairings might preclude the free flow of 

 water necessary to obtain realistic data; this 

 should be considered when locating the in- 

 strument, as well as the possible influence of 

 the submersible itself upon the data. 



.Attachment 



Every submersible differs in the method 

 by which instruments may be attached; 

 there are no standard mounting racks. When 

 an instrument is attached below the vehi- 

 cle's waterline. the mounting configuration 

 should be designed for quick attachment or 

 release by divers. Towed vehicles — such as 

 ALUMINAUT and other large submersibles — 

 fall into this latter category. 



539 



