Owning a boat isn’t a cheap prospect. In addition to the obvious expenses like boat insurance and maintenance, it can take an awful lot of fuel to get your watercraft around. Even if you’re only using your boat a few days a month, the cost of gassing up your boat can really add up.

To make matters worse, it’s not like there’s a ton of information out there about making your boat more economical in terms of its fuel use. It’s not as if you can inflate your tires on your boat properly to save money on gas. (Although, inflating your car tires and your boat trailer tires may help with your vehicle gas mileage, of course.)

Fortunately, there are a few things you can do in order to save a few bucks at the boat gas pump. In many ways, it requires you to understand your boat’s displacement design. Some boats are designed with displacement hulls, and some boats are designed with semi-displacement hulls, while others are planning. Each has its way to improve fuel economy.

Displacement and Semi-Displacement Hulls

A boat with a displacement hull is designed to force its way through the water. It doesn’t creep up on top of the water, or “plane” much if at all. A semi-displacement hull will achieve a partial plane. A plane, whether full or partial, helps to reduce the amount of drag on your boat as well as the amount of waves you make.

These kinds of boats have a sort of threshold speed where it requires a lot more power and, therefore, a lot more fuel. To figure out what this maximum speed is, you need to multiply the square root of the waterline in feet times 1.34. This means that a boat with a displacement hull that’s 38 feet in length has a maximum speed of 9.2 knots. If you keep your boat under that speed, you’ll save a bunch of money on fuel when compared with going faster.

For a displacement hull boat, that maximum speed really is a maximum. You can’t increase your speed past that, no matter how much you increase the throttle. For a semi-displacement hull, you’ll get a slight speed increase for a significant increase in fuel use.

Planing Hulls

A boat with a planing hull is the most fuel efficient type. Your fuel consumption will increase with your speed increase.

One trick to save fuel with a planing hull is to limit the amount of time that the boat displaces water, before it gets onto the plane and starts to skim the water’s surface.  To do so, you don’t just jam on the throttle. Rather, you bring your boat up to speed at a quick but steady pace.

Photo via brendan.lally.