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How Big of a Motor Does My Boat Need

Ah yes, horsepower… a unit of energy defined as the amount of work required to lift 160 pounds three feet upward in one second, because that’s what a single draft horse could supposedly do in the late 1700s, when the unit was conjured up as a way to compare steam engines to horses.

To say the least, it’s an awkward unit for measuring modern, gas-powered watercraft. Yet horsepower (HP) remains our most popular way of talking about engine strength, so let’s dive in.

Converting Horsepower to Boat Power

When it comes to boat size, we usually like to talk in terms of length, but the horsepower you’ll need has more to do with weight, so let’s start with a quick (and very rough) conversion of boat size/type to expected weight.

  • A small fishing boat (under 18’) should weigh around 2,000 lbs., and likely no more than 3,000.
  • A large, seafaring craft of 26’, meanwhile, can be two or three times as heavy, around 6,000 lbs.
  • Cabin cruisers are even heavier by the nature of their design, and the fact that they tend to be larger craft in general. A large (30’+) fully-outfitted cabin cruiser can exceed 15,000 lbs.

And these estimates are only for traditional hulls. With a pontoon boat, for example, you might get over 20’ or 25’ of boat while still keeping the total weight around 3,000 lbs.

How Much Horsepower Do I Need?

The accepted rule of thumb for getting a boat to go 20 miles per hour across calm seas is that you’ll need one horsepower for every 40 lbs. of watercraft.

A 4,000-pound boat should therefore have about a 100 HP motor. A smaller motor will suffice if you’re using your boat for leisurely trolling on small lakes, but a larger setup will be necessary if you’re traversing strong currents (or if 20 MPH is just too slow for your needs). 

When you combine heavier boats with a desire for high speeds, your needs quickly climb to the 300 to 400 HP range, even for modestly sized recreational craft.

Don’t Overpower Your Boat

Having too big an engine can be even more disastrous to your summer plans than chugging along at 5 MPH because you’re under-powered.

Installing an engine too large for your boat will cause the stern to sit dangerously low in the water. With too heavy an engine, you actually risk sinking in your own wake.

Avoid motor math altogether by contacting the team at Rogue Jet Boats. Our experienced professionals can show you a full line of world-class aluminum outboard boats and inboard jet boats and recommend high-performance engines that will keep you boating in style all summer long.