mrpike1973 Posted February 21, 2013 Share Posted February 21, 2013 hi how do i figure a formula for horse power rating ratio. i have a boat rated for 30 hp i have a 25 hp on it now. how far off am i from the 30 hp meaning if i have a boat rated for 100 hp and i have a 50 hp motor on it. i would be 50 % of what it is rated for. tried to do the internet but couldnt find it. i know 25 hp is plenty for a boat rated for 30 hp but for the life of me i cant figure the formula out. i believe they say you should never under power a boat by 10% of what its rated thanks for any help. Quote Link to comment Share on other sites More sharing options...
delcecchi Posted February 21, 2013 Share Posted February 21, 2013 I thought it was 20%. But that is another issue. Take the HP of the existing motor and divide by the rated HP. (subtract from 100 percent if you want to). So a 25 hp on a boat rated for 30 is 25/30 or 83% of rated hp. Quote Link to comment Share on other sites More sharing options...
mrpike1973 Posted February 21, 2013 Author Share Posted February 21, 2013 thank you so much. i believe your correct 20% on the motor but like you said another story. thanks so much for your help i think 83% should move the boat fine hee hee . just wanted to know how to do it thanks Quote Link to comment Share on other sites More sharing options...
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