How Many Horsepower Can I Have ?

[VKRUE]

Is There A Formula For Caculating The Maximum Allowable Horsepower One Can Apply To A Boat / Transom?
I Have A 17' Plywood Boat With A Cuddy Cabin. I Do Not Know What The Original Engine Was. This Boat Now Has A 115 Hp Evinrude. Is This Too Much Power?

[mmd]

Assuming that your boat, fully laden, weighs about 2200 pounds and is about 7 feet wide at the transom, according to the formulae put forth by Transport Canada regulating powerboats, your boat is just about at the top limit of acceptable powering.

[VKRUE]

Thank you MMD. I was speaking to a friend @ work today who mentioned that the U.S. Coast Guard has a formula they use to caculate whether or not a boater is in compliance with his / her power rating. The formula is L X W X 2 - 90 ! Is this the same formula that you use ?
Thanks again.
VKRUE

[mmd]

No, the Canadian formula is a bit more complicated, taking in to account whther the outboard motor is remote or tiller steered, what the deadrise of the hull is, what the gross weight of the laden boat is, length, transom beam, etc. The resulting horsepower figures are a slight bit more conservative than the formula you posted.

[VKRUE]

Thank you again MMD. My precise measurements of 16' L x 6.5' W x 2 - 90 indicate a maximum H P rating of 118. I have not yet learned anything about "deadrise" or any of the other factors that you mentioned. Either way, I should be O.K. with a 115, Thank you very much for your reply.
Looking forward to much more learning, maybe someday will build my own boat, closer to 38' L.

VKRUE

[Ike]

The Coast Guard actually has three formulas depending on the type of boat, and a seperate scale for little boats. For a 17 foot boat with remote steering and a 20 inch transom height, the formula is L X W X 2 - 90. W is the maximum transom width, not the maximum beam. A common mistake. If you go to http://www.uscgboating.org/safety/boatbuilder/index.htm you'll find their boatbuilders hand book. If you get confused on this, I've done this calculation probably a million times so let me know.

[lewisboats]

Here is a PDF of the Pamphlet

Steve

[VKRUE]

Ike:
Thank you very much for your info and the link.

Also thanks to Lewisboats for same.

Was not aware of having to measure width at transom, am now !

I have downloaded the pamphlet for future reference, thanks guys.

VKRUE

[Ike]

By the way. There are some math errors in that pamphlet. I worked with the guy who wrote it, and helped review it. How we missed them is beyond me. Anyway, make sure you double check your calculations. The formulas are all correct though.

[VKRUE]

ROGER THAT IKE........... Thanks Ike !