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Upgrading Boat Motor Capacity?


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G'day Raiders,

i have a 2005 Quintrex 475 Freedom Sport bowrider , It has a 2005 Mercury 75hp 2-stroke on it, it goes well but it is a little bit underpowered when towing wakeboarders. I would like to upgrade to a 90 Hp Honda V-tec but the compliance plate states that the hull is only rated to a maximum 80 hp. The transom is rated to 175 kgs (I think), the Honda weights 163 kgs so i don't think weight is an issue.

My question is, what would be required to make the hull capable of taking the Honda V-tec and roughly how expensive would it be, or would it all be too hard/expensive to get recertified?



Edited by Mrwooley
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You might look into the 75 or 90HP Etecs . Very tourquey for their size , and quiet and economical . Perhaps a pod to extend the length and bouyancy of the vessel may be an option.

Before giving up on the engine you have , what size prop are you running? It may have been delivered with a too tall prop , great for top speed , but a bit sluggish getting out of the hole. It can be likened to trying to start your car in third gear . The incorrect prop can possibly do damage to the engine.

Im sure Huey will have the right suggestions for you .


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Barry went through the same problem less the wakeboarders, mate it's best to speek with the boat company(quintrex) and see if they will upgrade you plate from 80 to 90, if that fails and the boat isnt under warranty speek with a marine surveyer and he can take a look at your boat and tell you what you may need to adjust to bring your rating up.

Hope this helps.

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Hi Barry Your 2005 model Mercury is a pretty late model mate. It would be a shame to have to buy another motor for the sake of a gain like that and in an alloy boat manufacturers recommendations as to motor size to suit hull rating is important.

Motor and hull compatability in plate boats is a different kettle of fish. IE standard factory V custom.

I wonder if the horse power of your 75 can be increased via the carby as they do to with 9's increasing them to 15 and increasing 20's to around 25 and more, to get the same result ?


jewgaffer :1fishing1:

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Besides warranty the other issue is insurance. If your boat is rated to 80hp and you are running a 90hp and something happens your insurance company will say "see ya". This is the same as if you are running your car on bald tyres.

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Hi Barry, as the guys have mentioned the warranty will be a problem but more of a worry will be the insurance. Unless you get it in writing that they allow you to fit a 90HP to a boat only rated to 80HP than you are going to have a problem. In our experience no insurance company will do this-they use the manufacturers HP rating as a guide.

That said, I have heard good reports about the new 90HP Honda, but if you are after more performance I do not think you will get it going from the 75HP Merc (which is tha same engine as the 90HP Merc) to a 90HP 4-Stroke. Low down performance or torque to plane the boat when pulling skiers or boarders would be in the favour of the Merc in my experience.

If the inusrnace company allows it and the dealer guarentees that the Honda will outperform the Merc, then it is your call, but I would want it in writing that it will accerate better than the Merc.

A cheaper option would be to fit a prop more suited to pulling skiers or boarders like the High Five from Merc or making sure that the engine is propped so that you are seeing about 5200 at WOT.



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