What is the best shape for a boat?

A boat hull needs to meet two main needs; the load to be carried, and the resistance to its flow in the water.

A rowing skiff has only a light load to be carried, but must offer as little drag as possible. Lowering the drag is accomplished by making this boat long and quite pointed, and the skin is made quite smooth. The structure of the boat frame should be very stiff to avoid the skiff bending. The mass of the skiff should be such that it barely floats when loaded - any excess freeboard is excess weight.

A container ship on the other hand, tends to be (not quite) flat bottomed, so as to maximize the cargo space. It has a high freeboard to enable it to weather stormy seas without shipping water. (As distinct to an oil tanker which, since the cargo is totally contained, it is not important whether some of the ship becomes awash.)

The bow of a large ship these days will usually have a submerged bulbous bow, designed to provide an enhanced water splitting ahead of the ship, thereby reducing drag. The steel plates of which the hull is made, will be welded rather than riveted, again to minimize flow resistance.

In general, longer boats can travel faster than short ones, due partly to bow wave effects. Short boats such as tugs, traveling at speed, will spend all their time climbing up their bow wave. This is an expensive exercise.