decreases once again to the limiting moment (see Figure 5d) . Such a 

 concept employing say six tines would provide a solution to the problem 

 of the three-tined foundation that comes to rest with two tines high on 

 exposed rock, the third penetrated deeply into soft ooze in a crevice 

 where a single bearing collar is not sufficient. The multiple, 

 plastic-legged form may be impractical because it may not be possible 

 to develop a limiting moment connection with close moment tolerance, 

 say 30 percent. Without such close moment tolerance the stiffer legs 

 would end up supporting the structure alone, and the complex unit would 

 be reduced in function to a plain three-tined affair. 



Confirming calculations have not been made, but it is estimated 

 that the "hydraulic" and "plastic-legged" concepts will weigh more per 

 ton pay load than the simpler three-legged and three-clustered varieties, 

 because the intricacies will add weight without increasing capacity. 

 A better approach to handling heavy loads appears to be to "ruggedize" 

 the three-legged unit, attach a tilt sensor/indicator, and simply re- 

 peatedly pick-up and set-down the unit until a satisfactory attitude 

 is indicated. 



Crushable Element Foundation 



The crushable element foundation was first conceived by engineers 

 at the Naval Underwater Center for possible use with their underwater 

 sound source mentioned earlier. Fifty-five-gallon oil drums, lying on 

 their sides beneath the foundation plate, were to function as crushable 

 elements to accommodate the microrelief of the rock surface and to 

 provide interlock. 



A brief search, as part of this report, was made for other materials 

 or systems that would serve as crushable elements besides steel oil 

 drums. Plastic foam-type materials were considered, but neither the 

 closed-cell nor the open-cell materials suffice: with known closed- 

 cell types, gas fills the cells, and the cells will collapse when sub- 

 jected to the hydrostatic pressure during lowering to the seafloor 

 (like a styrofoam cup) ; known open-cell types (like a sponge) will 

 fill with seawater on the way down and will largely return to their 

 original shape before contacting bottom; however, after contact they 

 will provide insufficient rigidity. Although apparently not available 

 now, it does seem likely that a plastic foam material having the re- 

 quired properties could be developed, considering the very wide range 

 of foamed plastic materials available with varying rigidities, densities, 

 pore sizes, and water absorption. 



Plastic or glass spheres with small holes for pressure equaliza- 

 tion do satisfy the requirements for a material that will not collapse 

 with increase in hydrostatic pressure and yet will be rigid. Such 

 spheres would be packed in a layer beneath the foundation plate and 

 then solvent welded, glued, or epoxied at their contacts to hold the 

 mass together. The problem with collapsing, tightly-packed spheres is 

 that the first sphere of a layer to collapse derives much of its support 



15 



