Maximum HP Formula

[MGuckin]

While trying to determine what hp I could put on my jon boat, I got a rule of thumb formula from an old timer mechanic. (Beam X Length X 2) - 90. It doesn't seem right. It would mean my boat, beam-4.25", length-12' would take 12 hp, but my 6'x 18' boat rated for 150 would only accept 126. If I change the 2 and use 2.25 instead the 18' comes out to 153 but the small boat comes out to 24.75.<br /> <br />Anybody heard of this? <br />Thanks,<br />Mike

 

[araiha]

Re: Maximum HP Formula

That comes directly from 33 CFR 183.53, which are the Coast Guard established standards for detrmining the horsepower on the label plate. It is more complex than just the formula. There are certain other criteria. There is also a test procedure. Link is attached. Go to 183.53 Horsepower capacity.<br /><br /> http://www.access.gpo.gov/nara/cfr/waisidx_99/33cfr183_99.html

 

[JB]

Re: Maximum HP Formula

Howdy MG. <br /><br />Alaskaskiff's advice is good. I think the formula is different for boats under a certain length, with short transoms or with tiller steer. <br /><br />Let us know what you find.<br /><br />Red sky at night. . .<br />JB

 

[MGuckin]

Re: Maximum HP Formula

Alaskaskiff and JB,<br />Thanks for the assistance. Yup breaks at 13'. I now understand, I think. Formula I posted still brings within tolerance I determined, but I now understand the break off point in hull length and transom dimensions. I do have a full transom and height falls within tolerance so no problem. All I really wanted to know was if I could hang a 9.9 on it and yes I can. It just the formula thru me for a loop when I used it for both boats. <br />Thanks for the input.<br />Mike

 

[MGuckin]

Re: Maximum HP Formula

I forgot to mention that there is no plate on the jon boat.<br />Mike