On Mon, 01 Jan 2007 12:34:08 -0500, Matt O'Toole
wrote:

The rule of thumb for this is 2hp per ton of displacement. So a 20 ton
boat would need 40hp to reach hull speed, and a 50hp diesel to operate at
80% capacity (another rule of thumb).

But this doesn't take wind or waves
into account.

Or hull shape, bottom condition, engine/propellor configuration, etc