Results 1 to 19 of 19

Thread: tunnel jon with tiller

  1. #1
    Member
    Join Date
    Feb 2008
    Location
    anchorage
    Posts
    69

    Default tunnel jon with tiller

    i would like to ask a question of the experienced members of the forum. i have a place near lake creek and the only real boating i do is up and down the creek and some on the yentna. i have an 18 foot G3 jon boat with a 40/30 jet. when the water levels are down there are a couple of choke points that get real shallow that i just barely cant get past. like everywhere else close to anchorage the number of fishermen is growing out there every year. i prefer to run upriver and fish for trout and i would really like to be able to run shallower to get away from the crowds. would a tunnel jonboat with a little larger engine make a significant difference or would just a larger engine with my current boat make a difference. i'd appreciate any input/thoughts from those with more shallow water experience.

  2. #2
    Moderator AKmud's Avatar
    Join Date
    Oct 2005
    Location
    Wasilla, Alaska, United States
    Posts
    3,185

    Default

    I had a 16' Lowe tunnel with a 40 Johnson (jetted). It ran really shallow, but the tunnel introduces a lot of air bubbles which robs a lot of power from the jet unit. The tunnel design was from the early '90s which was squared off and about 4-6" deep. The newer tunnels are shaped differently and not nearly as deep which may help deal with bubbles.

    One thing you may think about is adding trim tabs to your existing boat. Several guides on the Little Su are adding 10-12" deep pieces of 3/16 aluminum braced on either side of the motor which effectively lengthens the boat hull and increases lift. I have seen these modifications welded on, bolted, and even put on piano hinges with turnbuckles so they can be adjusted like regular trim tabs. It would be a cheap experiment to see if it gives you enough extra edge getting through the skinny water.
    AKmud
    http://i78.photobucket.com/albums/j96/AKmud/213700RMK1-1.jpg


    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  3. #3

    Default

    Weird, I had the same experiences as AKmud. Actually I was pleasantly surprised with the power of the 40/30 Johnson jet with a new sleeve and impleller. I had 1000lbs of people and gear in the boat and it performed far better than I ever expected. But, even with a center console, the stern would sink down in the water more than other non tunnel boats I have rode in. With a stern drive I would expect the stern to sink even further in the water depending on the tunnel design. What I did like about the 6" tunnel is I could completely beach the boat and the foot would not touch bottom. It's a compromise I suppose. Also the boat was light enough to unstuck by myself in most situations.

    I'm sure the ligther package you are contemplating will suite your needs just fine. The more horsepower you have the faster you will travel, which means less reaction time, but it will take you longer to get to point B and back with a 40/30 jet. I would love to find out if the 3" tunnel is a great compromise between a 6" tunnel and no tunnel at all.

  4. #4

    Default Flotation Pods

    Beavertail Mud Motors sells welded flotation pods.
    I bought some about 3 years ago and put them on a Skiff.
    They cost $350 and Silverstreak welded them on for another $350.
    They level the boat out, compensate for engine weight & extend the planing surface, and help knock down and ride up and over following waves if you stop suddenly. See attached photo.
    Attached Images Attached Images

  5. #5

    Default

    Quote Originally Posted by titobandito View Post
    Beavertail Mud Motors sells welded flotation pods.
    I bought some about 3 years ago and put them on a Skiff.
    They cost $350 and Silverstreak welded them on for another $350.
    They level the boat out, compensate for engine weight & extend the planing surface, and help knock down and ride up and over following waves if you stop suddenly. See attached photo.
    Thats a nice set up you've got. With that v-hull, how shallow can you go? Also, how fast that that mud motor push you along?

  6. #6
    Member OzAK's Avatar
    Join Date
    Oct 2007
    Location
    Fairbanks Alaska
    Posts
    175

    Default

    Hi gents, I'll weigh in here with some practical experience with tunnels and jon boats. Current owner of a couple of rock pounders, the one in question that mostly matches your jon is a 20' Lowe with a 90 V4 Johnson. Horsepower is somewhat irrelevant here for now, just what will that tunnel do for you. I ran my boat for a couple of seasons as I got it, with no tunnel and grew tired of pounding my jet foot on whatever manner of submerged junk I seemed to be able to find. I really didn't hit the boat too much, just the foot. Sez I "I've got to get that foot up out of harms way" so did some looking, reading, and studying of whatever boats I could. NOTE here.... By design, the Lowe factory designed tunnel that appeared in their early offerings were absolute crap, garbage, worse than no tunnel at all. By design, they just didn't work. Too deep with the side configuration, length to depth ratio, angle, you name it.
    Short story, took Skil saw in hand, cut large hole in aft center of boat-that took some hard swallowing at first- bent up a tunnel I designed, welded it in, built some sponsons for the transom for added floatation to offset the lost buoyancy from cutting in the tunnel, and never looked back. Best mod I could have ever done. My tunnel is 3" deep (just enough to get the foot even with the bottom of the boat-not the strakes, the flat bottom) and I can't even remember the last time I hit the outboard. I don't cruise fast as a rule, just steady, 22-25MPH upstream, 4400RPM if I'm light. When it gets really skinny, push it up a bit and skim across.

    I think you would be pleasantly surprised what a well designed tunnel would do for you, even without a repower. Just make sure your impeller isn't all chewed up, the liner is in OK shape and they are adjusted for the proper clearance. Those three will keep you pushing well, probably do what you seek. BTW- the tunnel worked so well I just figured I got lucky and managed to get it right by luck of the draw. Was it a fluke. Nope, have done a couple more for guys, all worked well, hold tight in turns, no ingested air for cavitation, shallow runners. Good luck, Oz

  7. #7
    Member tboehm's Avatar
    Join Date
    Nov 2006
    Location
    Soldotna AK
    Posts
    2,407

    Default OzAk

    you can't just share a story like that and not show pic's What up with that?

  8. #8
    Member
    Join Date
    Feb 2008
    Location
    anchorage
    Posts
    69

    Default

    ozak, thanks for the input. do you think that just going to a tunnel and keeping my current 40/30 jet would be a step up by itself? mostly i just have me, my wife, and our 75lb dog in the boat and fishing gear. occasionally we take friends and can have 4 adults. with 4 adults it takes much longer to get on step. i have wondered if i am getting the most out of the engine i do have. over the last few seasons i have drug the foot over a lot of gravel and have gotten used to taking off the foot to get the rocks out of the grate and from around the impeller. there are some small nicks in the impeller. how do you tell if they are too big, ie at what point do you get a new impeller. also how do you know if your shims are adjusted properly? thanks for any input.

  9. #9

    Default Ozak???

    I have a Lowe Roughneck 1960, the bottom is as flat as a pancake other than the strakes, I've been told that a tunnel will not work well on a flat bottom, is yours flat or does it have some deadrise? do you you have any cavitation issues? will you share more of your design dimensions?
    19' Lowe Roughneck
    90/65 Honda 4 stroke
    Outboard Jet

  10. #10
    Member
    Join Date
    Jun 2007
    Location
    FAI
    Posts
    2,294

    Default the challenged

    Got to give old Oz a break. He is a great welder, but challenged many other ways. Now, sit back, and enjoy his response. Ought to be a dandy.
    OzAK's boat is a flat bottom riveted. I have pretty much the same boat in a Quachita w/out the tunnel. I keep thinking about having that old crust bucket of an Oz do some work on it. I have an 88 on mine, so we are powered the same.
    One of the things I like about the pods Oz added was that if you jump a log the motor is still protected after the transom goes past the log. Looks similar to Tito's, but a bit beefier.
    Your motor should suffice if you keep you loads down. Do you have a stainless or aluminum impellor? Take it to your dealer and compare the leading edge to a new one. That is one sign of wear. Big nicks are hard to file, but can be done. I always set my impellor up to touch the sleeve, then raise it back by one shim. I like it close, maybe even closer than other guys. Just make sure the nut and lock washer are in place correctly.

  11. #11
    Member OzAK's Avatar
    Join Date
    Oct 2007
    Location
    Fairbanks Alaska
    Posts
    175

    Default There's a reason he chose 'RAT' for a handle!!!

    OK you Pinhead! I can get away with this because we're friends. As for the posting pictures, I'm working on it. With my ISP and connection, Photobucket takes some time to upload. Besides, I'm computer challenged. The only thing electronic I really understand are the controls on the front of a welder. I'd almost rather weld than run my boat. But that's almost.

    To answer other questions, Lowe & Slow, I approached that challenge the way I do everything- what can I do to make it work in the face of everyones negativity. My Lowe is as flat as a floor. In all honesty, it's true, flats don't like a tunnel much. Perhaps I got lucky on the first one, but after the second one worked very well, luck changed to something else.
    I started this way-what does it take to keep a jet from cavitating?-Bubble-free water. On a flat bottom it's harder but due to the design of the structure of the Lowe or any other boat, you tend to have to work within some parameters that the design makes you do, in this case ribs were the issue plus a keel. If you do some reading on tunnel design, mostly geared to semi-v boats, the length-to-width ratio is really quite close, ie not real long vs. width. A classic example of this can be seen on the bottom of a Wooldridge Alaskan II and others I'm sure. Because of the ribs, and keeping in mind the flat bottom, I chose to chuck the theories overboard and go the Oz seat-of-the-pants-what-makes-sense-to-me route. Before you say anything, yeah, this has gotten me into an adventure or two in the past, but no scars no story!! The last rib would have fit into the tunnel design criteria but was too close for my liking. My memory is fogged right here as I havn't seen under the floor in awhile but I believe I went with the 3rd rib fwd of the transom. My thought was to start the tunnel further forward than most giving whatever turbulence the chance to dissipate before it got to the jet. I made sure to cut the keel at about a 10 degree angle, long sloping cut and capped it with a piece of flat stock cut to shape. Any tunnel is going to affect your speed and load carrying ability so I kept it shallow @ 3" measured without the strakes in the equation. I used 1/8" 5052H32. Length as I recall ended up @ 40"-48" (whatever rib is in that area), very slow angle, cut it with a worm-drive Skilsaw, cutting the ribs to the angle of the sides of the tunnel.

    ATTENTION: Here's what I consider the "secret" of all this- When you want more air through a given area, compress it and make it speed up to do it. Pressure will drop unless it is "captured" and told what to do. Same with water, but liquid in effect doesn't compress, so as with water over a rock and into a flume, and because in this case the bottom of the boat creates the confines it has to work in, make it work for you. I made the aft end of the tunnel just wide enough to feed the jet water when the motor was turned lock-to-lock, no more. The front however, I made about half again wider, making that given water flow push its way into a smaller space. It all sounds good in theory. Works for me in this case.

    Side angles are 45*, that's what the saw can be set at. One thing I noticed IMMEDIATELY when I drove it for the first time was the handling. The tunnel was like adding 2 big strakes for control, it steers like it's on rails as compared to before, no sliding in turns, etc.
    Transverse welds ie the one at the very front of the tunnel was blended in to the point of being very smooth where the water enters the tunnel. This is important, you must keep things smooth.
    If you have power trim you can play with it underway and figure out where your motor cavitates. I don't have it but leave my motor set as low as I can and still not be below the strakes.

    You will read and it is absolutely true that flatbottoms tend to cavitate more running downstream and worse if you have a tailwind and it's choppy. The tunnel adds to this a bit I'd say, but it isn't really bad at all. I just run the edges where there's less chop where I can, stay out of the pressure waves, and cruise on. Sometimes it helps adjusting the power setting up or down and finding the sweet spot for those conditions.

    Lakecreek, make sure all your inlet grate bars are as straight as possible (parallel), you will stick less gravel between them. Not knowing much about the condition of your outboard or its age I can't tell you if there's a possible problem ie just a tired two stroke. Assuming it's not, my best suggestion for you is www.scottandjenn.com/outboardjet/ . Good education there on your jet with good pictures and explanations. Later guys, hope I didn't bore you. Oz BTW- I make patterns of everything I do so as to have repeatability with what works. If it works, I keep it, if not, adios.

  12. #12
    New member
    Join Date
    Mar 2008
    Posts
    1

    Default

    I will chime in with my 2 cents. Without a doubt the most important thing in jet boating is weight distribution. You have to get the boat to ride as flat as you can to maximise your shallow water capability. If all the weight is in the back of the boat then you will sit 3-4 inches deeper in the water than if you can get weight in the front of the boat. It is simply the law of physics. Think of a teeter totter, you need to balance your weight to make it ride flat or one side will sink deeper than the other. If your motor weighs 200lbs and you weigh 200lbs and you have a 13 gallon fuel tank that will weigh in about 90lbs, then you have 490lbs of weight in the back of the boat that you need to figure out how to offset. The easiest way to distribute your weight is to have a forward mounted console so you can sit in the front of the boat to help keep the bow down, by pushing the bow down it brings the back up, allowing greater clearance. To answer your question though, Yes, a tunnel will allow you to go a little shallower under certain circumstances. It must be a good quality jet tunnel. There are many tunnels out there, but most of them are designed to be used with prop outboards. A jet tunnel should not exceed 3 inches deep. with a 3 inch tunnel you will be able to mount the motor exactly even or maybe a hair higher than the bottom of the boat. Like I said earlier, a bow mounted console will give you the best weight distribution, but many people like having an open floor plan with a tiller model. In these instances the best option is to have a bow mounted fuel tank to add extra weight to help keep the bow down. In my personnel opinion, SeaArk makes the best boat on the market. Like I said, my opinion. My reasoning behind this is I believe they make the best designed jet tunnel and also you can get a factory installed bow mounted fuel tank to help with the weight distibution.

  13. #13

    Default

    Hey all. I have a 20f seaark, no tunnel. I am interested in the sponsons. How is your performance on turns? I see that every one like the hole shots but know one says much about the cornering. This is as important to me as the hole shots because I like to go where its skinny and tight corners. thanks

  14. #14
    Member
    Join Date
    Jun 2007
    Location
    FAI
    Posts
    2,294

    Default Hey you!

    Pinhead? Hey, I resemble that remark you old crust bucket! I'll remember you like welding more this summer when I can't find you to get any work done cause you are getting your boat wet.
    Back in the day, I mean way back in the dark ages, a wide boat was 48". I remember old Bill Page racing us up a creek in his 16' narrow flatbottom with a 33hp prop tiller on the back. We had a 20'x52" w/ a 70jet and we could not hardly get around him. Those boats with a tiller handle like a sports car and are incredibly responsive.
    Lakecreek, the more I think about your set up, the more I like it. Another 10hp and a tunnel would be groovy, but not a necessity for most of what it sounds like you will be doing. Going a little faster will get you out of the water a bit more, but then you'll need to carry more gas for the extra consumption.
    Dilemmas. What is a guy to do?

  15. #15

    Default Message to Oz

    Hi Oz,

    I enjoyed reading about your tunnel designs. I plan to display at the Fairbanks outdoor show next month. I'd enjoy talking with you while I'm in the Fbnks area.
    I sent you a private message to your form mail.

    Jim King
    Alaska Series Inflatable Boats,
    The Toughest Bottoms in the Business,
    River Rafts, Catarafts, Inflatable Kayaks,
    Inflatable Canoes, Inflatable Sport Boats,
    Inflatable Jet Boats, Tenders and Dinghies.
    WWW.alaskaseries.com
    (907)248-2900

  16. #16

    Default Web Site With Good General Information

    If I got a new engine............... I would definitely get the jet foot fins to help channel water into the foot espec during cornering.........

    http://www.fish.state.pa.us/boatcrs/jet/jetboard.htm

    Another link from the manufacturer of all outboard jet lower units:

    http://www.outboardjets.com/BoatSelection.htm

  17. #17
    Member OzAK's Avatar
    Join Date
    Oct 2007
    Location
    Fairbanks Alaska
    Posts
    175

    Default jet fins

    They work well but be aware that they can act like a trim tab and make the stern rise to the point that the boat plows water, out of trim unless you load more weight to the stern. 2 cents, experience with my Lowe. Oz

  18. #18
    Member
    Join Date
    Feb 2008
    Location
    anchorage
    Posts
    69

    Default

    thanks for the links and the advice. for now i think i will try and get my jet running as well as possible and keep banging the rocks with my current boat.

  19. #19
    Member alaskanmoosehunter's Avatar
    Join Date
    Apr 2007
    Location
    Next to my trashy neighbor
    Posts
    362

    Default Jet fins

    Quote Originally Posted by titobandito View Post
    If I got a new engine............... I would definitely get the jet foot fins to help channel water into the foot espec during cornering.........

    Jet fins are good to have...But be aware that if your motor isn't trimmed up when you get into skinny water, the fins act like a small plow that kicks rocks up into your grate.
    Combat Vet by choice! Defender of this great nation and people (Which unfortunately also includes the stupid and the ignorant.)

    http://t1.gstatic.com/images?q=tbn:_R_ZqAiK-e_U0M:<a href=http://hometeamsonline.com/photos/hockey/ARCTICLIONS/Ice_Puppies_Logo_Light_with_shading.jpg target=_blank rel=nofollow>http://hometeamsonline.com/photos/ho...th_shading.jpg</a>

    Support Youth Hockey!
    http://www.hometeamsonline.com/teams...Y&s=hockey&t=c

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •