Research on bulbous bow ships 1

Abstract

The research reported in this paper has been carried out to investigate the effect of large bulbous bows on the resistance and propulsion of a ship. The basic shape of the investigated bulbs was a sphere, connected to the ship in such a way that the original hull form was maintained as much as possible.

The basic ship was a fast cargo liner of 150 m (500 ft) length. Her trial speed corresponds to about ${\mathit{V}}_{\mathit{s}}\mathrm{/}\sqrt{{\mathit{L}}_{\mathit{f}}}=0.90$ . The application of a bulb of conventional size and shape would not favourably affect the resistance in the speed range of interest. The application of a bulb based on a big sphere, however, did reduce the required power at equal speeds. For the ship under consideration this reduction was 8.9 per cent. at ${\mathit{V}}_{\mathit{s}}\mathrm{/}\sqrt{{\mathit{L}}_{\mathit{f}}}=0.90$ .

The size of the sphere, needed to reduce the bow wave system as much as possible, was determined by a simple approximative theory. The experiments concerned in the first instance the location of the sphere relative to the bow, the effect of a variation of the diameter of the sphere and of the angle of entrance of the water lines of the ship.

When the ship was fitted with a large bulb faired into a more conventional shape, the resistance curve of the ship obtained the character of that of a ship one or two knots faster than the basic ship.

Finally the effect of a bulbous bow was compared with the effect of small changes in the main dimensions of the ship.