aluminum jon boat question -- tunnel hull aluminum jon boat question -- tunnel hull
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    aluminum jon boat question -- tunnel hull
from Paul (  
1/28/2006 1:25:00 PM


 I'm looking into buying an aluminum jon boat and a 9.9 hp motor.
I was wondering if I could better my performance by going with a tunnel hull or if I should stick to a standard jon.
My two primary questions are:

With a 9.9 hp motor, will the tunnel hull experience less drag and possibly a slightly higher speed or is the only major advantage being able to maneuver shallow water?

In choppy water, will there be much of a difference between the two in the smoothness of the ride with a small motor and lower speeds?



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   Have one, and here are some experiences. from Dougie (  1/28/2006 3:51:00 PM
I used to own a 15 foot long x 42" bottom Duracraft with a 25 Merc. (non tunnel). Since we fish part of the year in 12" deep marsh ponds for redfish, and bream/crappie/bass fish in shallows quite often, I got the urge to buy a tunnel hull. This is what I learned:

The flats that the marsh guides use are typically LONGER (18 to 22 feet or longer), and NARROWER (36" to 48" bottom)tunnels. The longer length allows the boat to float FLAT in the water, that is, the motor doesn't sink the back end down into the water. Therefore, the boat floats with less draft..or shallower.

I bought an 18' long x 44" wide bottom (Allweld brand) tunnel hull. I put the 25 Merc on it, and the first problem I encountered is that the motor needed to be raised because the manufacturer didn't build the transom high enough to compensate for the tunnel that was installed. I installed a very small jack-plate from BPS which solved the height problem.

Another problem: The motor would easily cavitate (vent) in turns, etc. with my stock aluminum prop. A visit to a local custom prop shop to discuss the matter enlightened me as to the need for a special prop for the setup I have. The prop shop had designed their OWN prop blades, had stainless steel castings for the blades and hubs made, and poured at a steel foundary. They said they sell about 500 props a year to tunnel hull people. Your normal prop for a 25 is a 13 inch pitch. These guys add a blade, and reduce the pitch to 11 inches. Ironocally, the boat runs the same speed as with the stock 13, but now doesn't vent. The prop is over 200 bucks, but was worth it for my purposes.

(Except as follows)

When you are running in any kind of chop, the tunnel boat is so long, that waves will cause you to get prop slippage. It doesn't take much to make it slip and I've trimmed it every which way, but in a chop, it happens to me.

Now some people actually 'vent' their tunnels to induce air into the prop's stream. I've never figured the advantages, but most tunnels used by the guides are vented. They have a pipe welded to the floor of the boat that sticks up along the back seat to a level as high as the gunnel. It induces air under the boat and they swear by it. I think the air prevents the boat from being sucked DOWN to the bottom in very shallow water on takeoff. Perhaps I'll look into venting my hull.

My opinion? In general, from a performance standpoint, a tunnel will cause you more tradeoffs than advantages. However, when the boat is being fished from with no power, it has all the advantages. It floats 'flat' in the water while fishing, and the motor SELDOM has to be raised to go over objects such as a shallow log. In the 12 inch ponds, we sometimes raise the motor because the skeg will drag in the mud a bit. It's really almost like fishing in a regular boat without a motor on it.

Oh, one more thing. I think the tunnels lack reverse performance, because the prop in reverse can't pass the water under the boat, but has to funnel it through the tunnel. The other disadvantage, is when in reverse, if you over-rev by the slightest amount, the prop is going to stack water right up against the transom, and over the transom it comes into your boat.

On the trailer, I had to devise a special roller for my transom jack to be in a proper position, but that's just another problem that was overcome.

Your decision....but, many times I've thought, if it weren't for the 12" deep pond fishing, I could easily get by with a non-tunnel. Actually we did for years out of the 15 x 42 Duracraft.

Oh..with a 9.9, my boat would be a SNAIL. If I was going to power anything with a 9.9, it wouldn't be a flat over 15 foot long, and no wider than a 42 inch bottom.

Your decision... Hope this helps.


   wuz amazed at how shallow they will run from beartrap  1/28/2006 6:59:00 PM
had opportunity to duck hunt last week in south La. and the guides routinely ran those boats in 6 to 12 inches of water.....the prop wash was always black and the prop was turning in a mixture of water and soupy mud....these guys used All-Weld boats,I'm guessing 18ft long with 40 h.p. short shaft Mercs(tiller steer)....they ran a hose from the motors pee hole around the transom,clamped to gunnel of boat up next to where driver sat so he could watch the end of it to see if the motor was pumping water....I watched it and it pumped about as much mud as it did water......I'd guess those boats were running somewhere around 30 thinking seriously about getting me one that I can use to fish rivers with......

   Tunnel Boats from pmgoffjr (  1/29/2006 9:15:00 AM
I've run and rigged more than a few tunnels for fishing S. Texas bays and marshes. Here's the facts.

The ONLY advantage to the tunnel is to be able to run shallow.

You will sacrifice: Speed, your idea of a 9.9 will not work at all. Handling, when you turn, it will get air in the tunnel, and cavitate badly. It's the way things are. Rough Water, without a hydraulic jack plate, because your prop is so high, rough water will be a pain. Backing up, No tunnel hull backs up worth squat. You'll have to run a prop designed for a tunnel, Power Tech makes a great one, but that cheezy aluminum stock prop will just sit and spin.

But...if you need to seriously run in 6" of water, it's do it, properly setup. I can run in four with mine easily, but it's at the limit of current equipment.

   Hard bottom problems too from Dougie (  1/29/2006 11:40:00 AM
What the above posts/info also shows is that tunnels work great on a soft, soupy bottom, such as the marshes described and RUN in shallow water. They don't necessarily START moving well in shallow water which is probably a misconception of most people. A tunnel at rest, barely floating over a hard bottom of dirt or sand won't just get up on plane when you gun it to go. The boat will drag the hard bottom and not be able to speed up to a point where the boat will rise onto plane. You just bump along, and the prop will overspin, sucking air. Rocks or gravel bottom? Forget it. In these cases, You need to idle to deeper water (which the tunnel boat will do better than a conventional boat) before you can get up on step. In muck, as the posts describe, they will throw mud and water like a firehose, and will slowly overcome the muck and rise onto plane, wherein they amazingly keep going. They really are a tradeoff, but you just have to accept the limitations if you really want one.



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