How do I size a motor for a boat?

[Angler of Repose]

How do I figure out if a motor's weight is too much for my boat? I have a 16' Mirrorcraft open boat and wonder if a 15hp bigfoot at 115# would be too heavy for it?

[fishkisser]

Find out the maximum HP of your hull rating
and check out the weight of a 2 stroke motor of that HP range ...
That will give you a starting point as far as max poundage ...

[Jrr]

You also need to keep in mind gallons of fuel and placement of the tank when running and your weight. Look up manufactures web site and remember these specs are for an average size person? ? I would estimate 150 lb person so that works into the equation, so subtract additional body weight from the engine power weight rating.

[Tinman]

One horsepower per 30 pounds of weight gives you 30 mph top speed. So total up the loaded weight of the boat, including gas, motor,boat, people, ice, anchor, gear, lunch....everything. Divide that number by 30, and you get the motor horsepower needed to push the boat at a top speed of 30 mph.

For example, if the loaded weight of the boat is 900 pounds, then 900/30 is 30 hp. You would need 30 hp to push you at 30 mph.

Another rule of thumb is go with about 80 or 85% of the maximum rated horsepower. You can find the max rated horsepower on the boat's nameplate.

[DJD]

How do I figure out if a motor's weight is too much for my boat? I have a 16' Mirrorcraft open boat and wonder if a 15hp bigfoot at 115# would be too heavy for it? You should be fine; maybe even a little underpowered!

[CRD4Liberty]

Bigfoot motors are designed for trolling motors, heavy work boat, and any type boat that has a displacement style hull (party boats, sailboats, etc.). Not, Not, designed for a planing hull and trying to get somewhere in a resonable hurry. A regular engine will do a much better job for you on plane. Your boat has a recommended HP rating on the required Coast Guard tested hull tag. The HP rating was derived from average motor weights, not the actual HP of the motor. My Bayrunner 15 have a 30 hp max rating, the Yamaha 30 I have on it does just fine as far as freeboard in a tiller drive configuration.

[Tinman]

[QUOTE=CRD4Liberty; My Bayrunner 15 have a 30 hp max rating, the Yamaha 30 I have on it does just fine as far as freeboard in a tiller drive configuration.[/QUOTE]

What a great boat the Bayrunner 15 is! I had one for 16 years, with a 25 horse Evinrude tiller steer, rope start. With the high bow it is a great rough-water boat for its size. I still miss that boat....end of hijack

[Dan Feller]

I would say if the boat is rated at more than 15 HP it should be fine, if it is only rated to 15 HP the added weight and thrust of the Bigfoot may be too much.

I have a 25 HP Bigfoot on my 14' Zodiac. The Zodiac is a really light boat (the boat actually weighs less than the Motor) but I load a lot of weight onto it at times. When I go crabbing I load up six pots, coolers, buckets of bait, ice, and my somewhat hefty neighbor and the boat still gets right up on plane with an 11 pitch prop.

I top out at about 35 MPH, which is plenty fast most of the time. I have a 13 pitch prop which will get me a faster top speed with just a couple people, but it doesn't work well loaded.

I like the added thrust of the Bigfoot when playing around on the tube as well - I can whip around an adult on the tube or kneeboard pretty well with only 25 horses.