縱列矩形板型彎曲部龍骨の横搖防止効果に就いて

抄録

It was published in 1938 that the angle of roll among waves of the Netherlands torpedo boat G. 15 fitted with streamlined fin bilge keels had been about 70 per cent, of that of a sister boat, the G. 16, When such a discontinuous construction is adopted for bilge keels, not only their area is much reduced for the limited total length but also the lift coefficient is diminished by the interference of adjacent fins. Hence if the aspect ratio and clearance length ratio of fins are not properly determined in accordance with the speed of ship, it will often occur that the fin bilge keels are less effective than the normal ones.
The details of bilge fins of the G. 15 are not clear, but those adopted for the passenger motorship “Oranje” after the excellent performance of the G. 15 had an aspect ratio of 9.5 and a clearance length ratio of 3.3. In the model experiments carried out in our experimental tank in 1940, bilge fins of an aspect ratio of 5.0 with clearance length ratios of 3.5, 3.0 and 2.5 were tested and it was shown that all of them were inferior to the normal bilge keels. In the present experimental investigations with model ships rectangular plates were adopted instead of streamlined fins. This is for the reason that the lift coefficient of a rectangular plate with aspect ratio up to about 5 is almost equal to that of a streamlined fin with the same aspect ratio, and that the initial cost is small when they are fitted to ships and moreover it is very easy to convert the normal bilge keels of existing vessels to this type. The aspect ratios of the model bilge rectangular plates were 8.0, 6.4, 5.0, 3.58, 2.78 and 2.0, their clearance length ratios being 3.0, 2.53, 2.0, 1.5 and 1.0. From the experiments carried out on the effect of these bilge keels it was found that the aspect ratio and clearance length ratio of rectangular plate bilge keels which would give a greater roll-stabilizing effect than the normal ones could be determined according to the speed length ratio of rectangular plates. For all the speed length ratios in the range of experiments the rectangular plate bilge keels with aspect ratio of 5.0 and clearance length ratio of 2.0 was the most excellent and showed to be 1.5 to 2.5 times as effective as the normal bilge keels.
In order to investigate the effectiveness of the new type of bilge keels on actual ships, bilge keels of three Aomori-Hakodate ferries of different types were reconstructed. With these three ferries and their sister ships were carried out experiments on the rolling among irregular waves on their definite voyages for two months. From the results obtained it was found that for all types tested the angles of roll of ships fitted with the new type of bilge keels were on the average about 40 per cent. less than those of their sister ships.