In order to preliminary investigate effect of HDS (Highly Ductile Steel) on the crashworthiness of struck ship, a series of large scale 3-dimensional ship-ship collision analysis are carried out using the non-linear finite element code LS-DYNA. A very large crude oil carrier (VLCC) is assumed to collide with midship region of another double hull (D/H) VLCC in right angle (90 deg.). Two collision points for the struck VLCC are assumed. One is between Swash Bulkhead (S.BHD) and Oil Tight Bulkhead (OT.BHD), the other is just on S.BHD. Damage extent and total absorbed energy until oil cargo tank ruptures in the case of HDS are compared with those in the case of conventional material. Critical colliding speed (VB,cr) is also compared. Effects of HDS on absorbed energy and VB,cr are discussed in detail. It can be found energy absorption by inner shell (IS) rupture with using HDS is about 2–3 times larger than that with using conventional It is also estimated that IS rupture does not take place when a striking ship collides in less than 8kt in the case of using HDS although a critical striking velocity in the case of conventional bow is about 4–5kt.

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There has been hot discussions on the characteristics of wave-induced pressure fluctuation on the side shell of VLCCs, since considerable number of fatigue cracks were found on side-longitudinals of second generation VLCCs. In Japan, it was mainly dealt with by SR-216 Panel, where a full-scale measurement on a typical second generation VLCC, tank experiments on a scaled model and theoretical investiga tions were carried out. The main themes of the discussion seem to be whether characteristics of pressure fluctuation is predictable even for small values of wave-length to ship-length ratio like 0.1-0.3 and how peak-to-trough value can be obtained of wave-induced pressure fluctuation on the side shell close to the load-water-line. Tank experiments on a scaled-model ship were carried out at Nagasaki Experimental Tank of Mitsubishi Heavy Industries to answer the questions, and it is shown that measured results agree with calculated results by strip method after a simple correction on non-linearity effect caused by the crossing of free-surface.Results of long-term prediction with the same correction also show good agreements with the results of the full-scale measurements.

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