THE FAILURE OF THE ONOMICHI-MARU

The 66,874-t 15-year-old bulk carrier Onomichi Maru was one of several large ships lost in the North Pacific during the 1980-81 winter; while she was proceeding at 5.25 knots, carrying coal from America to Japan in approximately Beaufort 8 conditions, her forecastle suddenly bent up through about 5 deg, oscillated for about 2 hr and then dropped off; the rest of the ship, about 85% of its length, sank 40 days later. A paper published as a result of a Japanese Government enquiry into this loss appears to be the only attempt to explain any of these 1980-81 losses; it offered the explanation that this loss could have been due to the combination of an unusual wave, large heaving and pitching, slamming, and other factors. The present Authors discuss this explanation, and suggest that there may be a simpler and more fundamental answer: that the vessel suffered massive fatigue because of narrow-band resonance. This hypothesis is presented in some detail; it is stressed that it is a hypothesis and not an assertion, and may be relevant to other losses. It is recommended that further investigations should be made by other parties and should include comparative experimental tests on the properties of mild steel subjected to random loading when the principal stresses do, and when they do not, fluctuate in direction; other aspects that should be investigated include fatigue studies for all ships that have been lost for unexplained reasons. If the Authors' hypothesis is thought wrong, any objections to it should be properly presented; it is a matter that should not be dropped,