Apparent Failure Mode of the Israeli (INS) DAKAR Pressure-Hull
By Bruce Rule - Oct 7, 2014
A Jun 2013 MIT doctoral thesis in Ocean Engineering (see last paras for details) describes failure modes for the hydrostatic collapse of test cylinders. One mode involves deformation and failure along the entire length of the cylinder.
A former British T Class diesel submarine recommissioned as the INS DAKAR was lost in the Mediterranean in Jan 1968 while in transit to Israel. A schematic derived from imagery obtained when the wreck was located in 1999 indicates the DAKAR pressure-hull appears to have failed along a significant part of the entire length of the structure: “from the control room to the stern.”
One of the main propulsion electric motors was reported to be located in the bow. Collectively, these observations suggest the DAKAR pressure-hull collapsed – initially well aft - at great depth creating a water-ram that tore the motor loose from its mounting and forced it through all the intervening bulkheads.
When SCORPION collapsed at 1530-feet, an after compartment was “telescoped”within a forward compartment by a distance of 50-feet in less than 0.112 seconds: the duration of the compression phase of the collapse, i.e., half the reciprocal of the bubble-pulse frequency of 4.46 Hz. Those values correspond to an average forward velocity of 300 mph for the after compartment.
As discussed by postings archived on this site as commentaries by the writer, the estimated collapse depth and the actual collapse depth (of the pressure-hull or a bulkhead with the same depth rating) are known for THRESHER, SCORPION, MIKE and the K-8 NOVEMBER. Respectively, these values in feet are: 1950/2400, 1050/1530, 5000/5630 and 985/2020. Actual collapse depth exceeded predicted collapse depth by an average of almost 50 percent with no value of less than 13 percent.
If the DAKAR pressure-hull survived by a similar margin beyond the predicted collapse depth of 626-feet, collapse would have occurred at about 900 feet (400 psi). This assumption is consistent with the condition of the wreck – especially the location of the propulsion motor - and suggests the pressure-hull of the DAKAR was intact until it collapsed.
The separated stern section of the DAKAR is in actual contact with the midsection of the wreck at a depth of almost 10,000-feet after falling as separate sections through about 9000-feet of water, an observation consistent with conclusions derived from analysis of acoustic detections of the loss of SCORPION: all sections of hydrostatically destroyed submarines sink nearly vertically.
MIT DOCTORAL DISSERTATION (OCEAN ENGINEERING), JUNE 2013: “ANALYTIC AND NUMERICAL STUDY OF UNDERWATER IMPLOSIONS”
Author of dissertation: Lynn Andrew Gish. B.S., United States Naval Academy (1993) M.M.E, Catholic University of America (1994) S.M., Massachusetts Institute of Technology (2004) Naval Engineer, Massachusetts Institute of Technology (2004)