Anyone ever do a DIY tunnel in a tin boat?

[TexasJim]

I've got a 14-foot v-bow tinny, and I bought and modified a jack plate for it, with 6" set-back and 3-1/2" lift. My 15 HP Yammy 4-stroke just didn't work at anything above 1" lift above pad. I asked a local expert tunnel skiff builder what shape a tunnel should be, and for a tin boat, a 5-sided shape should work best. I envision a 3" high tunnel, 10" wide, with 45 degree corners, tapering to the front. I could do that in .063 5052-H32, without too much grief. My skiff goes 20+ mph with two up, but I would like to go a little bit shallower. I know my prop isn't maximized for this situation, but I'll wait to optimize that. Just wondering if this group of experts have any experience on this/ Thanks, TexasJim

 

[Still Afloat]

Look on the outboardjets.com website for tunnel info. This drawing on their site is specific for outboard jets but, it might give you some ideas.

 

[TexasJim]

Thanks for that link. It's not very different from what I had planned, but I hadn't even considered extending it past the transom. I won't be using an outboard jet, but with the right prop, that would probably work. Good ideas. TexasJim

 

[Axhammer]

I would use the same thickness sheet for the tunnel as the hull skin.

 

[hunterguy86]

I've got a 14-foot v-bow tinny, and I bought and modified a jack plate for it, with 6" set-back and 3-1/2" lift. My 15 HP Yammy 4-stroke just didn't work at anything above 1" lift above pad. I asked a local expert tunnel skiff builder what shape a tunnel should be, and for a tin boat, a 5-sided shape should work best. I envision a 3" high tunnel, 10" wide, with 45 degree corners, tapering to the front. I could do that in .063 5052-H32, without too much grief. My skiff goes 20+ mph with two up, but I would like to go a little bit shallower. I know my prop isn't maximized for this situation, but I'll wait to optimize that. Just wondering if this group of experts have any experience on this/ Thanks, TexasJim

It help to find a good prop shop to add some cup to your prop. I had a guy work a Powertech SRA3 for my 4 stroke Yamaha F25. I can pick it up 2” or so with the jack plate and the prop still bites just fine. My little Jon boat with run in about 6” of water with no tunnel.

 

[thill]

The same thickness or maybe a gauge or two thicker, but that's just me. The tunnels I have seen have always been sturdily built, since they may be contacting the bottom or rocks or whatever.