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Tunnel Design and Dimensions

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Tunnel Design and Dimensions

Postby smllmth_bass » Wed Sep 27, 2017 8:04 am

Hey guys,

I am going to be building a new boat soon and wanted some input on how to best design the tunnel for optimal performance. The boat I am going to be building will 16ft long and 52 inches wide with a 3 degree dead rise. I will be running a 60/40 Mercury 2 stroke on this boat. The welder I plan on using hasn't built a tunnel before and boats aren't his main line of work but is extremely skilled so if give him dimensions and a plan he will have no problem doing it correctly. Any pictures or plans would be greatly appreciated.
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Re: Tunnel Design and Dimensions

Postby steelheadfreak » Wed Sep 27, 2017 9:23 am

Take a look at a Wooldridge tunnel design and go from there. If the tunnel is not just right, it will run like crap.....
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Re: Tunnel Design and Dimensions

Postby smllmth_bass » Wed Sep 27, 2017 9:40 am

I have tried to track down dimensions for that and came up empty. Would you have a source? I am trying to improve on the performance compared to the design I have on my current boat as it cavitates some in choppy water. Other conditions it does great but I feel there is probably something better out there. My local jet builder built my current boat and that is why I want to go with someone else to build my new tunnel. If some one could measure a woolridge tunnel and provide all the angles and lengths I would be eternally grateful.
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Re: Tunnel Design and Dimensions

Postby steelheadfreak » Wed Sep 27, 2017 12:20 pm

smllmth_bass wrote:I have tried to track down dimensions for that and came up empty. Would you have a source? I am trying to improve on the performance compared to the design I have on my current boat as it cavitates some in choppy water. Other conditions it does great but I feel there is probably something better out there. My local jet builder built my current boat and that is why I want to go with someone else to build my new tunnel. If some one could measure a woolridge tunnel and provide all the angles and lengths I would be eternally grateful.


With a 3 degree deadrise, you will get some cav no matter what in chop. Id suggest a minimum of 6 degree or better yet a 9. You will run all the same water and get a little less air intake. Lots of info on this site for tunnels. Use the search and you should get everything you need.
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Re: Tunnel Design and Dimensions

Postby jl8jeff » Sat Sep 30, 2017 8:20 am

It's going to be hard to describe it but I'll try. I have a Lowe 1652 Roughneck jet tunnel. The front where the tunnel begins is 15" wide. As the tunnel goes back, it slowly gets taller until it's about 2" high at the back. The top of the tunnel tapers in as it goes back and it measures about 12.5" wide at the top back of the tunnel. The bottom of the tunnel is still 15" wide at the bottom back, so that makes the sides of the tunnel taper inward as it goes up. I don't have the overall length written down and the boat is still in the water for the season so I can't get the length until it's on the trailer. Here's a couple pictures I took of the tunnel before it went in the water for the season. I might be pulling the boat out in about a week or 2 depending on the weather so I can get full measurements then.
Attachments
Lowe_tunnel1.jpg
Lowe_tunnel2.jpg
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Re: Tunnel Design and Dimensions

Postby smllmth_bass » Mon Oct 02, 2017 9:44 am

Awesome! Many thanks!
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Re: Tunnel Design and Dimensions

Postby fishing66 » Tue Oct 03, 2017 4:49 am

Here is a precise schematic from Outboard Jets. I had a tunnel cut into my prior rig and the welder used .25 6061 aluminum. He also fabricated a new transom knee that was welded directly to the tunnel.
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tunnel.jpg
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Re: Tunnel Design and Dimensions

Postby fishbum » Sun Nov 12, 2017 1:49 pm

Here are a couple Picts of tunnel I have used on several of my boats. Two keys for me. When the bottom is cut out for tunnel you leave a flap that you lift enlightenment to get the tunnel unit in place then instead of having a butt joint at the front that flap is bent down to make the lid
Of the tunnel. also as with Wooldridge the tunnel is made so the water dumps into the tunnel and has a flat spot to the intake instead of a ramp '
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IMG_3345.PNG
This is Wooldredge
IMG_1249.JPG
IMG_0954.JPG
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Re: Tunnel Design and Dimensions

Postby smllmth_bass » Tue Feb 20, 2018 8:09 am

Hey guys thanks for all the advice on this project here are a couple pictures from last night putting the tunnel in.

IMG_1019.jpg

IMG_1021.jpg
Last edited by smllmth_bass on Wed Feb 21, 2018 1:19 pm, edited 1 time in total.
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Re: Tunnel Design and Dimensions

Postby Ahusk » Tue Feb 20, 2018 5:52 pm

You may already know this but don't leave those strakes blunt ended like that. Build some pieces to taper them back into the hull. They may be far enough away from the pump shoe that it won't matter
Last edited by Ahusk on Tue Feb 20, 2018 8:39 pm, edited 1 time in total.
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Re: Tunnel Design and Dimensions

Postby MT sauger skiff » Tue Feb 20, 2018 8:17 pm

I have no idea what the tunnel dimensions are.....having said that, it appears to be deeper than needed. Additionally, I can't say that there was an advantage to extending the tunnel past the formed strakes which are meant to provide rigidity to the hull and may only induce turbulence at this point.

Kudos for having the courage to cut what looks like a fresh hull and curious to know how it performs.
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Re: Tunnel Design and Dimensions

Postby smllmth_bass » Wed Feb 21, 2018 9:35 am

It was a big leap to cut a brand new boat up but I have supreme confidence in my machinist and he has done a great job. The tunnel is right at 2 3/4" inches deep so it is a quarter inch deeper than the specified depth. Also the lip of the tunnel lines up with the edge of skrates in this picture how ever they have been tapered so that they are further forward. It is slightly wider and this was an oversight on my part by trying to adhere as closely as possible to the recommended specs. If it does cause issues I plan on cutting them further forward and building the rigidity back in on the inside of the hull. This was the not quite done product. The pictures were taken after the tunnel was tacked in. Hopefully this weekend I will get it painted, rigged, and carpeted so next weekend I can get it on the water to test it.
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Re: Tunnel Design and Dimensions

Postby smllmth_bass » Tue Mar 13, 2018 7:26 am

Hey Guys,

Got the boat out this weekend to do some testing. It ran amazing. Light Years ahead of my old boat. I hopped up on step very quickly (within a bouat length give or take), had great top end even on a bigger wider boat, ran shallow and never once tried to blow out even in some pretty good chop and tight turns. It still needs a paint job but aside from that she is all ready. My buddy even caught a pretty good one out of it.

Thanks for everyone's input.
Attachments
unnamed (2).jpg
unnamed.jpg
unnamed (1).jpg
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