A bulbous bow is a protruding bulb at the bow (or front) of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability. Large ships with bulbous bows generally have a twelve to fifteen percent better fuel efficiency than similar vessels without them.

Bulbous bows have been found to be most effective when used in vessels that meet the following conditions:

Thus large vessels that cross large bodies of water near their best speed will benefit from a bulbous bow. This would include naval vessels, cargo ships, passenger ships, tankers and supertankers. All of these ships tend to be large and usually operate within a small range of speeds close to their top speed. Bulbous bows are less beneficial in smaller craft and may actually be detrimental to their performance and economy. Thus, they are rarely used on recreational craft like powerboats, sailing vessels, tug boats, fishing trawlers and yachts.