# tunnel hull jon boat



## carson (Jun 5, 2009)

I want to add a small pocket tunnel to a 1436 jon boat.I have the means tools and skill to do the metal   work but just don't know what size tunnel.Is there some formula to go by? I know added tunnels can be trouble but I'm bored. Any input would be greatly helpful thanks.


----------



## anytide (Jul 30, 2009)

the wider it is the better/sharper it'll turn @ speed before it blows out, but your gaining more draft as it grows.


----------



## Brett (Jul 16, 2008)

My testing showed it to be:

Draft of hull at rest = height of tunnel
Diameter of propeller plus 4 inches = minimum width of tunnel
Height of tunnel in inches = length of tunnel in feet

The shape is up to you whether oval, rectangular, trapezoidal, or a combination

My project hull while I was figuring it out:

Pocket Tunnel


----------



## disporks (Jan 19, 2011)

not sure where you are located, but if there is a boat dealer near you that sells tunnel hulls I'd go in there and just check em out...or come to swla lol we got TONS of em here


----------



## anytide (Jul 30, 2009)

> My testing showed it to be:
> 
> Draft of hull at rest = height of tunnel
> Diameter of propeller plus 4 inches = minimum width of tunnel
> ...


so what did we learn from all this Mr. D ?


----------



## Brett (Jul 16, 2008)

Learning is fun?  ;D

Wait a sec....I know the answer to this one....

Ya' wanna run shallow? Get a jet!


----------



## WhiteDog70810 (May 6, 2008)

I don't know the math or the "why", but I think tunnels work better on bigger hulls. I suspect it is because you need a wide transom and some minimum length to support the motor necessary to generate the speed to create the suction to make the tunnel draw correctly so you can actually raise the motor up. I don't think a 1436 has the bottom area to make it worth the effort. I think you will cut a hole in an otherwise good boat to make a boat that is less functional. Others will chime in though.

Nate


----------



## anytide (Jul 30, 2009)

> I don't know the math or the "why", but I think tunnels work better on bigger hulls.  I suspect it is because you need a wide transom and some minimum length to support the motor necessary to generate the speed to create the suction to make the tunnel draw correctly so you can actually raise the motor up.  I don't think a 1436 has the bottom area to make it worth the effort.  I think you will cut a hole in an otherwise good boat to make a boat that is less functional.  Others will chime in though.
> 
> Nate


good point, i used big tabs for some lift and wide tunnel for turns...worked well with enough power behind it...


----------



## carson (Jun 5, 2009)

Thanks a lot guys. the boat is rived so its really light.It would be powered by a 20 hp.is there a shape thats preferred?as for the ruining a good boat metal work is to me is like fiberglass is some of you so i could fix it.plus someone gave me the boat.what got me thinking was a guy at my local river had a 1832 paddle jon style with a tunnel and a 9.9 and he took me for a ride it seem to work great. unfortunately i didn't get the specks on it at the time.during some searching I found this vid call can your jon boat do this?on you tube and got me wondering...


----------



## carson (Jun 5, 2009)

Is that draft of hull at rest = tunnel hight with motor or bare boat?also the length how critical is that?


----------



## Brett (Jul 16, 2008)

Draft of hull at rest is about the same as draft at planing speeds due to hull running angle.
Tunnel length is calculated based on that same hull running angle, 1" of taper per foot of length.
Nothing is critical on a hull that short and lightweight! ;D


----------



## WhiteDog70810 (May 6, 2008)

> Is that draft of hull at rest = tunnel hight with motor or bare boat?also the length how critical is that?


Draft at rest is measured with the motor on the boat. If the tunnel is higher than draft at rest, you are getting in to the area of negative returns because the water will be more aerated coming out as you raise the tunnel height. If you set the motor high enough to take advantage of the beer foam that will result, you will blow out on on your hole shot. Hydraulic jackplates can help, but there is only so much shtuff you can hang off the back of a 1436.

I have no idea what that length should be. 

Nate


----------



## WhiteDog70810 (May 6, 2008)

So a boat that drafts 6" at rest needs a 6' long tunnel?  Holy smokes!



> 1" of taper per foot of length.


That is foot of length of the tunnel, correct?

Are you talking about the taper of the top of the pocket towards the bow? This is to minimize aeration?

I don't care to know the math, but the theory of fluid dynamics interest me.

Nate


----------



## Brett (Jul 16, 2008)

To obtain most efficient operation, the beginning of the tunnel
should be where the surface of the water first hits the line of the keel.


----------



## carson (Jun 5, 2009)

Thanks guys very helpful information.all the factory aluminum jons i can find pictures of seem to have short narrow tunnels.like shorter than 3ft why is this?not the small jet tunnels.Also some are sloped all the way back then some a lil higher at the entrance of the tunnel.seems a cone shaped tunnel would be most efficient.If the tunnels so long don't you have a cat hull?


----------



## mirrocraft (Apr 29, 2009)

Put a 35$ Doelfin on it and let it rock. It will plane better and keep the bow down.


----------



## Vertigo (Jun 3, 2012)

I've owned a lot of tunnel hulled boats, and the main thing I've observed is that the shape and dimensions on each tunnel on each boat have been very different. Obviously there are a lot of theories. The next thing I've noticed is that some work better than others. The best working tunnel I've had is on a SeaArk 1660 MVT and believe it or not it's very different from the tunnel on the very similar SeaArk 1652 MVT. It's also very different from the well respected Pathfinder 17T. Rather than try to describe the SeaArk tunnel here, I'd suggest you find one to measure and study, or at least check out some photos. Finally, to get any real shallow water performance out of a tunnel a hydraulic jack plate is almost necessary.


----------



## carson (Jun 5, 2009)

Brett was there a reason you chose a flat tunnel as a posed to sloped front to back?what about a wider front to funnel more water in the tunnel?


----------



## Brett (Jul 16, 2008)

Easier to modify a box by filling with foam
than cutting a tapered form and reglassing to reshape.

Too much horsepower needed to drive a funnel tunnel
compared to the cookie cutter slot of the box shape.
Once the vent shells were installed, the 5 hp nissan
was all that was needed to make the tunnel function.
The entire build was about learning epoxy, plywood
and seeing how shallow I could get with a home built hull.


----------



## CurtisWright (May 9, 2012)

Here is the tunnel insert for my Fowl River 16 in the bragging section. Its 6" tall, 14" wide and 7' long. I run a 40HP tohatsu and get 31MPH with a 11.5 x 12P prop on my 16' hull. It works great for me. 

It was formed by bending/screwing a thin triangular sheet of fiberglass to plywood. It was faired in and a mold was made from it.


----------

