When steam ships were first being designed, it became more important to have a hull shape that cut through water easily. Up until then the free supply of energy from the wind had been used to create the force needed to move sailing ships. Steam engines required coal, which cost money and had to be stored at various ports all over the world. To reduce the costs, ships had to be designed to use the least amount of fuel. To this end a special lab was built by the Royal Navy at Haslar, near Portsmouth. This was the first lab to consist of a large water tank and to use models of hull shapes to investigate how they moved through water.
When an object moves, friction opposes its motion. In water it is harder to move because water is denser than air. The opposing force exerted by water is often called drag. To accelerate a ship the engines must create a force that exceeds this drag and to keep it moving the engines must match the drag force.