I'd like to know what HP my boat was rated for

[SeaKaye12]

Hi,<br /><br />I have a 1978 Thunderbird TriHull. It's about 15.5 maybe 16 feet long.<br /><br />It has a 85 HP Merc on it, and it's original owner says he could have gotten it with a 115.<br /><br />Nowhere on the boat that I can find is a plate with HP rating on it. I see no evidence of a plate ever being there.<br /><br />I wonder how I can find this information? I'd also like to get an idea of how **HEAVY** an engine I could use...as I've noticed that the newer 2 stroke and certainly the 4 stroke engines are way heavier than mine.<br /><br />Then there's the issue of HP measured at the crank back in 1978...and at the prop now. So, a 115 today is really more powerful than they were back in 1978?<br /><br />Thanks for reading...I always enjoy hearing what you all have to say.<br /><br />Chuck

 

[ZmOz]

Re: I'd like to know what HP my boat was rated for

The capacity is determined using the formula length x width x 2 - 90. You'll get a ridiculous number not really related to the boat's ability to handle power, but that's how it's figured. The rating has nothing to do with the weight of the engine. To find out what the real life maximum is you need to either try out a different motor, or find someone with a similar boat and a bigger motor and ask them how it handles.