55 



Although It was Intended merely to determine the maximum allowable 

 depth of submergence, strain measurements were made at several points on the 

 skin of the float in order to provide a somewhat clearer picture of the man- 

 ner in which failure eventually occurred. These measurements were also in- 

 tended to determine to some extent the permanent strain that could be allowed 

 before the hydrodynamlc properties were affected. However, up to the point 

 at which the welds at the reinforcing rods failed, no deflections were visible 

 in the skin that might have affected the hydrodynamlc performance . 



Resistance-wire strain gages were cemented to the skin of the float 

 either directly over the ends of the reinforcing rods or at positions half- 

 way between adjacent reinforcing rods. Figures 4l and 42. Since these tests 

 were not intended to provide data for a complete analysis of the stresses in 

 the float, the gages were arranged to measure only the longitudinal strains 

 which were adopted as criteria of the allowable permanent set. 



RESULTS OP THE SUBMERGENCE TESTS 



The data obtained during the submergence tests of the planing float 

 are shown in Figure 42 as curves of strain in mlcrolnches at various depths 

 of submergence in sea water. The tests were stopped at three different depths, 

 and the pressure was returned to atmospheric in order to observe the permanent 

 set of the material. The signs adjacent to each set of curves Indicate the 

 direction of the strain, plus being used for tension and minus for compression. 

 Although some extremely high strains were recorded, the associated deflections 

 of the surfaces did not appear to be so excessive as to warrant additional 

 tests of performance since any differences would be within the experimental 

 error of the hydrodynamical characteristics discussed in the body of this re- 

 port. Complete failure occurred at an external pressure corresponding to 65 

 feet of sea water, at which pressure the reinforcing-rod welds failed In the 

 top surface and allowed collapse of tiie upper and lower surfaces. Photographs 

 of the float taken shortly after completion of these tests are shown in Figure 

 43. 



Although the design of the float was based on a maximum depth of 

 submergence of 40 feet of sea water, using "black iron" with a yield point of 

 30,000 pounds per square inch, the results show that the steel actually used 

 had a much lower yield point. The actual yield point of the material appears 

 to have been approximately 10,000 pounds per square inch, indicating that a 

 much poorer grade of steel had been inadvertently used than originally speci- 

 fied. Nevertheless, the present design is apparently controlled by the weld- 

 ment of the reinforcing rods. It was originally proposed that the ends of 



