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Building a jet boat

Postby sms986 » Tue Oct 13, 2020 9:41 am

Hello all,

I am starting the process of building a jet boat. I'm having a company in Illinois build the hull, a 22' 8 degree vee hull. I am putting two yamaha gp1200 engines in the boat. I'm mainly interested in the hull/intake design. I would like to use the entire jet pump assembly from the Yamahas because it is very simple. I'm going to have a few custom fittings made that allow me to bolt the jet drive through the transom. My main question is regarding the design of the intake duct. I could just mount each intake duct flush with the bottom of the hull, but I want to minimize sucking up air, especially on the high side when turning. Does anyone have any pictures of intake ducts for twin engine boats? Thanks!
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Re: Building a jet boat

Postby Reid01 » Thu Oct 15, 2020 10:17 pm

I guess you could look at Yamaha exciter boats or maybe that’s where you got your motors from? Big boat be neat to see how it goes. I don’t think you have to worry about them sucking air til your already spun right around but I’m gust guessin :Power: g
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Re: Building a jet boat

Postby jetboatwanabe » Fri Oct 16, 2020 7:06 pm

Check these guys out they have built a few mini twins :Drink1: :bash:
:chicken:


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Re: Building a jet boat

Postby heliwrench » Sat Oct 17, 2020 9:34 pm

If you are thinking of using the yamaha aluminum suction housings I would go a different route. They are very thin and will not take much abuse. They are prone to cracking if any rocks go through. I imagine you are planning on running shallow if you are building an 8 degree bottom. There are lots of options out there for beefier cast suction housings that have adapters to use the rest of the yamaha pump, or you can build them yourself.
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Re: Building a jet boat

Postby sms986 » Sun Oct 18, 2020 4:07 am

I was thinking of using the yamaha housings but now that you say that I may look elsewhere. I could also try to have my own made. I would like it as low as possible so that my engine sits as low as possible on each side. Is there any issue with the jet coming from the very bottom of the transom?

Also, can you point me in the direction of some of these aftermarket housings? Thanks!
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Re: Building a jet boat

Postby heliwrench » Sun Oct 18, 2020 9:07 pm

Jetstream boats sells a fabricated intake housing that has a stomp grate. It is a little cheaper, and is in canada so that makes it cheaper again with the exchange rate. RSR sells a cast one that has a straight intake grate (no stompgrate). There are other cast ones as well, they all look like they are very similar to me. None of them are cheap, but its a pretty important part of the boat. As far as height of the jet on the transom goes, I would say that they are all pretty much as low as possible, while still allowing for clearance between the crankcase and the bottom of the boat.
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Re: Building a jet boat

Postby sms986 » Sun Oct 18, 2020 10:25 pm

Awesome. I'll check it out, thanks.

On a side note, there is a carrier bearing mounted through the "transom?" of the skis that the intake housing slides into. I plan on having a 3/4" aluminum bulkhead here and putting a drain plug in the bottom, so that if one of the pumps blew up, the pump housing area would be completely isolated from the rest of the boat and I wouldn't go down.
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