O/B and Hull HP Ratings

[snagroms]

Just want your thoughts on the max HP rating provided on hulls. I have seen a few used boats recently with O/B higher than the hull is rated for. <br /><br />When the ratings are put to a hull are some of the considerations transom strength, boat speed, and motor weight? Anyone ever have experience with this before? <br /><br />I looked on line at an 18' and 20' model of the same boat. the 18 is rated 150 and the 20 is rated to 235. Seems like a large jump for just 2 feet of boat.<br /><br />Your thoughts before I buy would be great.

 

[dajohnson53]

Re: O/B and Hull HP Ratings

If you look at the US Coast guard site which addresses HP ratings for hulls, <br /><br />http://www.uscg.mil/d8/mso/louisville/WebStuff/comdtpubp16761_3b.pdf]Coast Guard HP guide[/URL]<br /><br />the factors they look at are: overall length, transom width (at the top), transom height, type of bottom (flat vs. V), type of chines (hard vs. soft), and remote steering vs. tiller. There may be some other factors, but that's what I remember. Of course, the strength of the transom is important, but the CG formula doesn't have an input for that. I also don't recall seeing any consideration for weight of the motor (e.g. difference between 2 and 4 stroke for a given HP). I believe what the CG is ultimately assessing, given the above factors, is how the boat will handle with a certain power pushing it.<br /><br />Not knowing the two boats you're looking at, the large difference in HP could be because the longer boat is also wider and has a higher transom, or a different type of bottom, just for example.<br /><br />For fun, if you know the dimensions on the two hulls, go to the CG site and run the numbers and see how it plays out. I ran them for my hull and it came out right on at the rated HP of 205.

 

[walleyehed]

Re: O/B and Hull HP Ratings

D., I ran my numbers of my boat just to see how it compared to the original BIA certification and it came out as 125 as a max. BIA plate says 150....there isn't enough difference in Crank rated vs. prop rated to account for this.....spoze they changed the numbers in the formula???

 

[dajohnson53]

Re: O/B and Hull HP Ratings

Originally posted by walleyehed:<br /> D., I ran my numbers of my boat just to see how it compared to the original BIA certification and it came out as 125 as a max. BIA plate says 150....there isn't enough difference in Crank rated vs. prop rated to account for this.....spoze they changed the numbers in the formula???

Good question - the only time I visited that site was the time I ran my own numbers. Where did you measure your transom? I know with mine, I measured at the gunwales, the very top of the transom (i.e. the widest part).

 

[ZmOz]

Re: O/B and Hull HP Ratings

Originally posted by snagroms:<br />When the ratings are put to a hull are some of the considerations transom strength, boat speed, and motor weight? Anyone ever have experience with this before?

Nope, not at all. Some of the most important considerations when deciding if a boat is overpowered too. That's why I laugh at people that throw a fit whenever someone goes 1hp over the rating...

 

[kirkland]

Re: O/B and Hull HP Ratings

I run my numbers through the calculation twice and i get 95hp but my plate says 75....any thought as to why....

 

[walleyehed]

Re: O/B and Hull HP Ratings

I "think" it's more of a recommendation for the manufacturer to follow if they wish to do so...<br />Some Bass boats come with an unlimited HP limitation (or lack of).<br />My numbers show 125 by USCG figures, my plate says 150, and my engine of choice is a 200. Boat handles quite well...I know some have issues with this but it works for me.<br />I don't know how they come up with the numbers they do....