I’ve seen enough of the hulls on some modern ships to notice that they seem to have a nub at the very bottom of the prow–it starts below the Plimsoll line and sticks out forward like a little thumb. Is there any advantage to this shape?
I am guessing that you are referring to the bulbous bow. (Yep, that is what they call it.)
Large ships that possess bulbous bows frequently have a small icon painted on the bow near the waterline that looks like an inverted question mark to warn people that the bow projects forward from the hull. A small fan icon means that the ship has a bow thruster–a tube through the hull with a side-facing propellor in the center that allows the ship to maneuver in tight spaces without needing the speed required of the rudder or the assistance of a tug boat.
Also, as long as we’re discussing ship’s prows, does anyone know why modern ship’s prows overhang considerably forward of the bow at the waterline level? I noticed in Titanic that the bow was almost completely vertical.
An overhanging prow will deflect water away from the deck when the ship encounters waves. You will generally notice that very sharply raked prows occur most frequently on cruise ships. Cargo ships and warcraft have a certain amount of rake, but only enough to get excess water away from shipside. (And beyond a certain point, it is simply fashion–even naval architecture is driven by fashion to a certain extent.)
Older ships were built with nearly all up-and-down lines vertical (or only mildly raked) because the naval architects were not sure of the strength of the iron and steel that they were using. As they became more comfortable with their building material, they began “playing” with it to produce shapes that looked faster. (To a certain extent, some shapes will reduce air resistance, but not enough to mandate the shapes that ships are given. Note that many cargo ships continue to have vertical islands for the crew and machinery cabins.)