With Boat Design, You Cannot Ignore Physics



The graphic above lists the forces experienced by a planning hull. When we are asked to provide engines or a complete propulsion system, these are the forces that we need to take into account. As engine manufacturers, we are obligated to recommend a specific engine for a project. Price or the amount of a sale never enters into these discussion. Our focus is on providing ample power to deliver a required performance level on a specific vessel. If one of our products is a good solution, then we recommend it. If not, we would rather pass on a project than deliver a customer something that will not deliver the proper performance level.

What the picture above illustrates is basic physics. For each force shown, there must be a minimum of force pushing against it in order to make the boat move through the water. We cannot provide something that violates these physical laws: That is magic and not engineering.

Vessel performance is a question of balance. For instance, if displacement is increased, we must either increase buoyancy, provide more power either through engine or propulsion, or shift the LCG of the vessel. Sheer horsepower is a variable of the equation, but not the only variable. Though the equations can get complex, here is the “quick and dirty” version:

Speed =( Horsepower per engine*number of engine)^.551/(Displacement )^.476 *2.74


By using what is known as the speed length ratio, or Froude Number:

text{Speed Length Ratio} =frac{v}{sqrt {text{LWL}} }


v = speed in knots
LWL = length of waterline in feet