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Outboard Jet on Tunnel Hull for Prop

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Re: Outboard Jet on Tunnel Hull for Prop

Postby MT sauger skiff » Tue Mar 17, 2015 12:31 pm

No you don't have to, you just need to be able to adjust the new tab which should extend about a far out as the one you have now
1960 MT Roughneck with 150 hp Johnson jet
1860 CJ Roughneck with 150 hp E-TEC jet
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Re: Outboard Jet on Tunnel Hull for Prop

Postby digi » Tue Mar 17, 2015 3:53 pm

How do I adjust the tab if it's welded? Sorry I'm new/dumb/slow, lol.
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Re: Outboard Jet on Tunnel Hull for Prop

Postby MT sauger skiff » Sat Mar 21, 2015 6:18 pm

Here are examples of the tunnel mod on my 1860. Fast hull and needed to keep impeller from barking at WOT in chop.

They are only OB jets, don't be picky and keep the following in mind when you decide how to do yours

Note that the whole tunnel doesn't need to be fully enclosed. Saves on welding since there really isn't much to be gained from a full taper.

Note that the plate was tacked and boxed at the back of tunnel, then added splash plate to keep foot fed trimmed and to play with tranducer installation in tunnel
Splash plate not needed in your case but would recommend extra material extending past the weld so that you can bend it slightly for your motor height.

Many ways to do this but one must always work around what they already have. This one keeps it fed over 40mph in chop
Attachments
splash.jpg
top chop.jpg
1960 MT Roughneck with 150 hp Johnson jet
1860 CJ Roughneck with 150 hp E-TEC jet
MT sauger skiff
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Posts: 865
Joined: Thu Aug 23, 2012 7:26 pm
Location: Great Falls, Montana

Re: Outboard Jet on Tunnel Hull for Prop

Postby digi » Sat Mar 21, 2015 7:25 pm

gotcha, that makes sense, thanks.

Last question before it goes into the shop :lol:

I'm assuming the tunnel should be wide enough to feed water into the jet foot when the outboard is turning as well right?

My welder is asking me how wide I want it. I'm thinking I'll just measure the full distance of the outboard turning left and right and that should be good?

greatly apprecaite it, can't wait to get this dialed in!
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Re: Outboard Jet on Tunnel Hull for Prop

Postby 208SnakeRunner » Wed Mar 21, 2018 9:48 am

Hey guys I'd like to revive this thread. I am looking at doing the exact same thing and stumbled into this discussion. Your tunnel is identical to mine. How did your setup turn out? I'm currently running a prop and I'm happy except when I find skinny water less than 10" deep (Snake River). I'm going to look at an old jet outboard this evening. I measured and it looks like a short shaft with jet pump will sit on mine at exactly the same height as yours in the pictures. Do you have cavitation issues? Anything else to consider? Thanks.

My boat is a Polar Kraft riveted 1752 with identical tunnel. Looks like my transom is a bit taller than yours though.
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Re: Outboard Jet on Tunnel Hull for Prop

Postby vol423 » Sun May 06, 2018 6:04 am

Could it be more likely that a bay kit is so named because they are made by Bay Manufacturing in Ohio? I have a boat manufacturer’s license and I sell mostly boats for outboard jet drives. Occasionally I sell one with a propeller tunnel. I rigged one such recently with an hydraulic jack plate and a Power Tech propeller where the propeller was above the bottom of the boat when in operation. But my point here is that a so-called Bay kit, which merely extends the shaft length by five inches, is not usually sufficiently long to permit the boat to operate properly. An inch or two more shaft length is usually needed. An Atlas manually adjustable jack plate, with a 4” setback and 4-6” of vertical lift, is sufficient to permit proper tuning of the propeller drive. Regarding the use of tunnel extensions past the transom, I find them invaluable for eliminating cavitation and splashing. I would always prefer that the nose of the jet foot tuck up inside the top of the tunnel extension when fully trimmed down.
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Re: Outboard Jet on Tunnel Hull for Prop

Postby vol423 » Fri May 25, 2018 8:38 pm

Regarding tunnel dimensions for a jet application to the propeller tunnel, you will benefit by putting in a filler to make the last section of the tunnel flat topped. I make my tunnels 4.5" high and extend them six inches past the transom. On the triangle topped tunnel, if that boat were mine I'd fill in the top of the tunnel to make it 4 or 4.5 inches tall forward to the point where the new flat topped tunnel intersects with the tapered section of the original tunnel. I would also extend it six inches past the tunnel on the top and sides. I usually will also rivet an aluminum splash plate to the top of the tunnel, bent up at about a 30 degree angle and stopping short of the jet drive by an inch when the motor is trimmed all the way down.
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