Right boat for my 10 Hp?

[kkj]

How does the HP/size-of-boat formula look?

 

[CATransplant]

Re: Right boat for my 10 Hp?

Interesting question....but difficult to answer. It all depends on how you want to use that 10 hp motor. It will probably plane most small 12-14' aluminum skiffs. Lots of folks use them on jonboats, as well, and they perform pretty well.<br /><br />Anything heavier or bigger and you'll just be pushing water and propelling the boat at its low hull speed.

 

[CATransplant]

Re: Right boat for my 10 Hp?

OK, I forgot who I was talking to. There just isn't a simple formula you can use. Weight, hull design, length...all play a role in determining how much horsepower it will take to plane the boat.<br /><br />The easiest way to see what's what is to look at the horsepower limits on a number of smaller boats. The ones that are rated for 10 or 15 horsepower will probably perform quite nicely with a 10 hp motor. If they're rated for 20 hp or 25hp, your 10 probably won't plane them. Any rating over 25 hp, and you'll just be mushing through the water.

 

[Paul Moir]

Re: Right boat for my 10 Hp?

Crouch's formula can be helpful for this:<br />Speed (MPH) = C / Square_Root(Displacement/HP)<br /><br />C is a constant which defines the type of boat, ranging from about 150 (heavy, deep vee boats) to around 200 (light, flat bottomed boats). For the sort of boat you're likely looking for, 190 would be a good C.<br />Displacement is in pounds and includes everything - motor, passangers, fuel and hull. Take for example the cottage tin utility hull with a 6hp 2-stroke outboard. The hull weighs around 200 lbs, engine 60lbs, 2 adults (~180 each) and a child (say, 80 lbs). That's 700lbs. Throw in say 50lbs of life jackets, anchors, fuel and oars. Now apply Crouch's formula:<br />Speed=190/sqrt(750/6)<br />=17mph<br />I measured a little over 16mph by GPS.<br />(please pardon all the imperial measures!)<br /><br />This post can be helpful as a reference too:<br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=17;t=038021

 

[kkj]

Re: Right boat for my 10 Hp?

Good answers to a my (hopeless) question, I must say!