The bulbous bow: why ships have a nose underwater

The bulb protruding underwater at the bow of most large ships is a wave-cancellation device. A hull moving through water builds a bow wave, and making that wave costs energy; the bulb builds its own wave slightly ahead and out of phase, so crest meets trough and the two partly cancel. On a hull that suits it, the saving runs to several percent of total fuel, enormous money across a 400-metre ship's life.

The catch is that the cancellation is tuned: a bulb works best in a band of speed and draft, which is why the slow-steaming era after 2008 sent so many container ships to drydock for 'nose jobs', their bulbs cut off and rebuilt for the new, slower service speeds. Some very modern designs, CMA CGM's LNG giants among them, integrate the bulb into a near-vertical bow profile instead of the classic protruding bulb.

You can read the bulb on every silhouette on this site: the small forward protrusion at the waterline on the container ships, tankers and cruise giants, and its absence on Titanic, whose plumb bow predates the idea, and on Prelude, which never moves.