Bulbous bows are important components that can reduce drag and increase efficiency. Bulbous bows are found on scallop boats, seiners, trawlers, and other large commercial fishing vessels.
Displacement hulls push water aside as they move. The water that is pushed aside forms a wave that begins near the bow. The length of this wave is proportional to the speed of the hull through the water.
At some speed, the length of the bow wave increases to the point that it matches the length of the hull, and the hull operates in the trough of the wave, with a peak near the bow and another peak near the stern. This speed is called the “hull speed” and it is approximately 1.34 times the square root of the waterline length of the hull.
The bulbous bow creates it’s own wave that is farther forward and “out of phase” with the natural bow wave created by the hull, effectively subtracting from the normal bow wave and reducing it’s drag-inducing effect.
A bow bulb can be optimized for a specific speed (or a small range of speeds). A bow bulb providing the greatest potential for reduced fuel consumption is generally designed at a given speed.