Don’t let the gloom and doom predictions of high gas prices keep you from your boating passion. Even with bulk oil costs soaring, it’s still possible to have some money in your pocket when you leave the fuel pier. By understanding your boat’s design – whether it has a displacement, semi-displacement, or planning hull – and doing some easy calculations, you will know the boat’s most economical cruising speed.
Displacement and Semi-Displacement Boats
Displacement hulls are designed to force their way through the water. A semi-displacement hull achieves a partial plane, which reduces drag and wave making. Both have a top speed that cannot be exceeded without increasing the power significantly. A large power increase also means greater fuel consumption.
To figure the maximum speed, multiply the square root of the waterline in feet times 1.34. Using this calculation for a 38 ft. displacement hull boat, the maximum speed is 9.2 knots. To save money on gas with a displacement or semi-displacement hull, do not try to increase your speed past the calculated maximum speed. In the case of the displacement hull, increasing power to go faster will use more fuel without a resulting speed gain. With a semi-displacement hull, your speed will increase, but there will be a corresponding fuel consumption increase.
Pull back on the throttles with a true planing hull. Fuel consumption increases with every knot while the boat is on plane. A boat with a planing hull has the greatest fuel economy at the point when it first comes onto plane, or begins to skim the surface of the water.
Limiting the amount of time a planing boat displaces water before coming onto plane will also result in reduced fuel costs. This doesn’t mean slam the throttle downs to get up on plane faster. Instead, bring the boat up to speed at a moderately quick, steady pace.
If you are like me, you like to go fast quickly. But, if you follow these tips for reduced fuel consumption, you will finish at the end of the boating season having won the fuel marathon with a few extra dollars in your pocket.