Boat rated for 140 HP, if you put a Jet pump on motor can you go larger?

[r49miner]

I read, not supposed to exceed horse Power rating. Using a Jet pump I should be able to use a 200 HP to equal 140 HP.

 

[GA_Boater]

Welcome aboard, miner.

I would think over 140 horses, no matter if it drives the boat with a pump, a prop or heaven forbid, sidewheels. the right people would have an issue. If something bad happens, the prop or pump isn't in the picture, only the horsepower. Equivalent horsepower doesn't count, be it at the powerhead or prop/pump. It's the HP rating on the boat placard and what the motor manufacturer put on the motor. IMHO

 

[r49miner]

First, Thank you for the Welcome and for taking the time to answer.
As to your "IMHO" normally I would say your right. You are right if the motor says a higher HP than what is rated for the boat; However, Most motors come with two ratings if I am not mistaken. And I could be mistaken. But a 115 HP also has a 80 HP for a jet, 115/80. If that is the case could you not go with the lower number and legally change the visible HP rating to reflect the lower HP if using a Jet?

 

[GA_Boater]

Ask a water cop or an insurance agent. In some locales, the water cops frown on changing the HP decals. Again - IMHO.

 

[Frank Acampora]

Most Jet pump engines deliver to equivalent of about 20% less horsepower. It is due to the fact that they develop full thrust at (0) speed and thrust drops off as speed increases. (the boat is running away from the water jet)

If you can find a 200 HP jet you will still be over the HP limit. Secondly, If you can find a factory manufactured engine of that size, it will be rated as the jet horsepower on the cover and the model number. THUS: if you find a (for example) Mercury jet that develops 180 HP at the prop--if it had one--then the engine will be rated a nominal 140 as a jet and you can use it. No issues with the law.

 

[r49miner]

Yeah, Something like that is what I believe but would check with a manufacturer or Coast guard before testing the theory. So now I'm off to Yamaha to see if that's the case.

Thanks Mr. Acampora and GA_Boater

 

[racerone]

The spinning impeller inside the pump wastes a lot of power due to friction.--------Go with the jet horsepower rating of the motor.

 

[r49miner]

I just contacted Yamaha about my question regarding two ratings of Horse Power. I was told to always go with the actual Horse Power of the motor because even though it's a Jet, the lower unit can always be changed to a prop. So although I thought a person could go by the lower HP because of using a jet proved wrong.

 

[ondarvr]

The HP reduction is considered 30% by the manufacturers. Yamaha has absolutely nothing to say about the legality of it, they may have an opinion, but it really means nothing. Many boats that are designed for the option of a jet will have both a prop and jet rating, along with a tiller or remote rating.

It mainly depends on where you live and boat, there is no federal law on HP ratings, only recommendations, although many people seem to believe the CG will ticket someone for being over the recommended HP limit, they can't. There are local regulations that may limit the HP though, so check that aspect of it. Insurance companies rarely consider it a problem, I actually asked a few, they just ask what the HP is and give you a quote.

If you get a little more specific with your question it may be possible to get an accurate answer, make model and size of boat, state you live in, etc.