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.