# Tunnel Jon Boat



## crespo (Sep 26, 2011)

Hi all, new here from South MS. Nice site and I've found a good bit of useful info about tunnel boats. I run a tunnel jon boat in shallow rivers and some marsh hunting and fishing. I have some questions about my current set up and would like to hear some opinions or get pointed in a better direction. I'll break it down as to what I have and what my set up is doing.

Rig:

I have a 1448 Weld-Craft Tunnel Jon boat. I have a 96' 50 Evinrude Tiller on it with a jack plate and trim tabs. I'm running a PowerTech 4 blade 17 pitch prop with a lot of cup. Right now the jack plate is almost all the way up and the prop shaft is lined up with the center of the tunnel.

Problem:

I'm having porpusing problems and only have 3 trim holes to play with. I can get the boat planed out and running in the middle hole and trim tabs bent down and inch or so with minimum porpusing but the nose is digging in. I havent had a chance to try it in the top trim hole but have it rigged up to take it out this weekend and try it with the trim tabs straightened out some as well. 

With the middle hole set up and before the last cupping of the prop I was hitting 31.8 mph on gps and ran in 5" of water without bumping anything. I was hitting the rev. limiter so I had the prop cupped more. I haven't checked speed with the gps since but it feels faster and I'm turning 5400 rpms @ wot. For that motor the max rpm in the book is 5500 so I'm right where I need to be on that now.

I've also looked at a lot of threads about the foils and have one halfway built to try as well. It's kind of a hybrid design off of what I liked in the pictures I've seen in the threads but I think it's a bit on the narrow side. It's 22" L X 12" W with 2" lips bent downward on a 40* angle and a 2" lip bent upwards on the same angle on the front. Does this sound good or should it be wider in the front?

Suggestions, comments, constructive criticism are all welcome. I feel the boat should run better than it was in the first set up I had and where I run my boat the most, everyone on the river is out to be the fastest and won't share much for tips or advice. I could care less about the speed, just want my boat set up right.


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## coachlaw (Oct 26, 2005)

Welcome, you anywhere near Pass Christian?

I'm no engineer. My knowledge is nothing but trial and error. 

There are 2 things you can do to deal with porpoising. You can put more weight in the bow, or you can put on an enlarged cav plate. There are many to choose from. I've used Shallowblaster and Manta Ray. Both are fiberglass, both work very well. 

My buddy had the same problem, but his motor was too small for one of my plates, so I got him a doel-fin from Academy. It did the trick.

Regarding speed, IMO it's pretty dangerous to go much faster than 30mph with a tiller.


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## patwilson (Jan 13, 2006)

Welcome! Got any pics of your rig?


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## RB II (Feb 26, 2009)

You didn't mention the trim position. Try tucking the motor under as much as possible, then work it outward until it starts to porpoise again. If it is already tucked under...then a hydrofoil of some type would be my next suggestion, it will basically take the place of the trim tabs and you can save them for the rough water.


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## crespo (Sep 26, 2011)

coachlaw, I live up in Picayune, about 45 minutes from the Pass. I'll have my version of a cavitation plate finished up this week and I can try my fuel tank and battery farther towards the front. Right now they're in the middle of the boat.



hydra, with the motor tucked under it porpuses real bad without the trim tabs bent down. I don't plan on rough water with an aluminum flat boat unless I have to. 

patwilson, I can post some better pics tomorrow but here's a couple.


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## longboat (Apr 14, 2008)

You can also add a 'hook' to the hull to reduce porpoising, but it's not the best solution - try the others first. Float pods/sponsons are also a possibility.

31 sounds plenty fast for that boat setup. If you need more speed, you can add a vent to the tunnel.

When you say trim tabs, do you mean the pieces of metal that are part of the hull that you can bend with a pliers, or are they SmartTabs, or the real ones that you can adjust on the fly? Also, is your jackplate manual or electric/hydraulic?


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## pmgoffjr (Jul 30, 2009)

I used to run a very similar setup, and here's what really worked well on my little iron rig...

Step n Trim trim tabs and a transom wedge will calm the porpoising down a huge amount, quicken your holeshot time, and make everything much easier to drive.


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## Red3Fish (Jun 4, 2004)

*Dont have a tunnel....*

but mine is set up for 2 people in the boat.....does fine. With just me, it wants to porpoise.....put longer hose on gas and battery, and does better, but not cured! LOL

Try putting a big hootered fishing partner in the bow and see how it does? LOL

Later
R3F


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## GuyFromHuntsville (Aug 4, 2011)

Red3Fish said:


> ...Try putting a big hootered fishing partner in the bow and see how it does?


And if it does still porpoise, well that's an added bonus:wink:


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## Stuart (May 21, 2004)

What position is that jack plate in the picture in? Looks like it is up, maybe all the way. If that's the case, you still have propbably 18" of motor in the water in that shot. Do you adjust your plate while underway? If not, I'd build up the transom and hang the motor straight off the back.


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## crespo (Sep 26, 2011)

Trim tabs are welded on aluminum that you bend with pliers, jack plate is manual and is about 1/2 inch from all the way up ( in the picture it was about 2" lower, also the boat was pulled up on the sand bar some and had the stern sunk down a little more), everything is manually adjusted on the boat. I'd really like to get away from the trim tabs all together as I occasionally have to jump a log and when doing that they get bent up and serv no purpose until I can get to a spot to bend them again. I almost have my cavitation plate finished up and will try it as well this weekend.

Here's a few shots of the motor/transom/tunnel.


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## CaptDocHoliday (Feb 3, 2011)

Cav Plate will help a ton. I run a Shallow Blaster.

Hotty Toddy


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## Stuart (May 21, 2004)

Thanks for the pics. That's a cool setup and a lot of motor for a 1448  I'd try a cav plate like mentioned and maybe a tiller extension and a stand up grab bar to get your body weight more centered.


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## crespo (Sep 26, 2011)

As I mentioned before I'll have my first version of a cav. plate finished up tomorrow since it's " Home Project Friday " at work lol. It's not the prettiest, I used scrap metal just to try it out, but I'll post some pics when it's done and on the boat. I have no problem keeping myself centered in the boat driving it as it is. I'm going to move my fuel tank and battery up to the front and try that as well.


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## spurgersalty (Jun 29, 2010)

I run a similar setup. 15/42 southfork tunnel with a 25 yamaha. Imo too much motor on a short boat. You need at least a 15' boat for that amount of weight. 16 would be better.
Also, cavitation plate won't solve anything because looking at the pics, when on plane, you will not have water high enough to reach the plate. Just guessing here. My plate is about 2" out of the water on plane.
Also, 31 is kinda slow for a 50, I'm getting 29.5 outta my rig with half the ponys using a 3 blade 13 pitch. I'm going down to a 12 pitch with a marsh cup. I want more lowend hole shot. I'm done with the speed thing.


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## crespo (Sep 26, 2011)

I agree it's slow for a 50 on a 14' boat. I'm tryin a cav. plate because I get a lot of water over the cavitation plate even with it as high as it is. I get good low end and get up on plane in 2 boat lengths but would think I'd be running faster with a 50 turning a 4 blade 17 pitch 5400 - 5600 rpm's.


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## SSST (Jun 9, 2011)

You would think, but if you don't have the water getting to the prop (cavitation), ur wasting alot of ponies. I wish I had that setup in my riverboat so I wouldn't have to buy 3 props a year.


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## crespo (Sep 26, 2011)

Heres' a couple of shots of the cavitation plate I built. It came out "ok" but if it works I think I'll build one that's wider and take a little more time on the cuts.


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## crespo (Sep 26, 2011)

I spent all day on the river running my boat. The set up with the cavitation plate works great. I even ended up bending the trim tabs up flat and had very little porpoising. I moved my two 6 gallon gas tanks to the front of the boat and that helped smooth it out even more. It gets up on plane in two boat lengths still and it ran 35.1 mph on gps. It's spinning the prop 5600 rpms consistently now. Guess all I needed was a little more water on the prop. Only thing left to do is pull the motor off and give it a good paint job. It will be the OD Green that my boat is with black Evinrude on the sides of the cowl and a question mark on the back where it said 50 lol.


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