The Hull formulae.

There are four basic formula regarding the hull form, they are;

• Planing Speed
• Block Coefficient.
• Wake Factor.
• Hull Speed.

Planing speed is the speed at which the hull will, in theory, plane, or stop acting as a displacement hull. Obviously in practice this will not happen, you could fill the hull of the example vessel with a bloody great V16 Detroit Diesel (have to be a 71, as I don’t reckon a 92 would fit) and you still won’t be able to ski behind it.

In practice, if you were lucky, it would travel along partly up on its own bow wave with the bowsprit pointing at the sky and towing a wake that would sink a lifeboat, but the chances of it managing to climb over the bow wave onto the plane are minimal. Inefficiency and fuel consumption would also be extremely high.    If you were unlucky it would dive under the bow wave or poop the stern under power and head straight for the bottom.

Block coefficeient is literally a theoretical block of material of proportions such that it performs the same as the real hull as far as the propeller trying to push it through the water is concerned.

Wake factor is how much water the hull “tows” behind it as it travels through the water. You will all be familiar with tugs and trawlers, which can create significant following waves from the flow of water back around the stern as the boat passes a particular point. Not to be confused with the waves made by the bows parting the water, which is covered by the block coefficient and C for the hull..

Hull speed is the maximum possible speed of a displacement hull, we will calculate this three different ways, and compare the results.