secure the hatch cover. On a number of 

 vehicles the hatch cover is secured to the 

 hull by metal clips which extend from the 

 hatch cover into and tangential to the pres- 

 sure hull. An example of this type of ar- 

 rangement is shown in Figure 9.18a. With 

 this method pressure could build to a point 

 where, when the vehicle is surfaced and free 

 of hydrostatic pressure, the hatch cover 

 could be forced upward sufficiently to inhibit 

 retraction of the securing clips. An alternate 

 solution might be to undog the hatch when 

 submerged, but this may lead to explosive 

 depressurization when nearing the surface. 

 To overcome the problem where the hatch 

 could not be undogged due to high cabin 

 pressure. International Hydrodynamics has 

 derived an alternative securing method 

 which is shown in Figure 9.18b and is used 

 on AQUARIUS I. This method consists of a 

 thick rubber strap affixed into a clip inside 

 the pressure hull. The philosophy here is 

 that the only time the hatch cover needs to 

 be held secure is when the vehicle is on the 

 surface (the strap provides this function) and 

 that ambient pressure will keep it closed 

 when the vehicle is submerged. 



To solve the pressure problem a number of 

 vehicles provide a thru-hull pressure relief 

 valve which allows the operator to relieve 

 the pressure when surfaced without opening 

 the hatch and at a desired rate. BEN 



FRANKLIN, for one, had such an arrange- 

 ment which could be used to "burp" the 

 pressure hull if so desired. 



While submersible diving history shows no 

 evidence of internal pressure buildup to dan- 

 gerous proportions, there is always the possi- 

 bility that it can occur and the seemingly 

 simple task of securing a hatch cover may 

 have important repercussions. 



Philosophical Approach; Two 

 Examples 



The duration, control and monitoring of 

 life support systems is finalized, not only on 

 the basis of the number of occupants, volume 

 of the cabin and length of dives, but also on 

 the operator's philosophy concerning safe 

 diving practices. Most operators agree on the 

 following: A supply of oxygen, a carbon diox- 

 ide removal system and monitors for atmos- 

 pheric pressure, oxygen and carbon dioxide. 

 But there are extremes on both sides — e.g., 

 the K-250 and BEN FRANKLIN. The former 

 relies on nothing but air within the cabin; 

 the latter supplies virtually every need for 

 life support. Before examining these two ex- 

 amples, attention is directed to a paper by 

 Mr. A. P. lanuzzi (10) who describes the 

 philosophical and technical considerations 

 that went into the design of DS-4000's life 

 support system. lanuzzi's report is an excel- 

 lent example of the considerations and trade- 

 offs a submersible designer must confront in 

 life support design and is recommended as a 

 practical primer for the neophyte. 



Most submersibles provide a life support 

 system paralleling that of the DS-4000, but 

 on both sides of this system are extremes 

 which are derived by virtue of the dive time. 

 K-250 has a lV2-hour dive duration; BEN 

 FRANKLIN has a 30-day duration. BEN 

 FRANKLIN remained under longer than any 

 other submersible and its life support system 

 is described because it was highly successful 

 and required virtually no electrical power. 

 Additionally, the results of the system's ef- 

 fect on the crew members were exhaustively 

 examined and documented; hence, there may 

 be one or more features of this proven sys- 

 tem which may be of value to future design- 

 ers and present operators. K-250 is dis- 

 cussed primarily because it represents a rad- 

 ical variation from every other design and 

 the designer states why in detail. 



437 



