Skinny water boat advice needed. Jet or Prop tunnels?

Discussion in 'Boats, Blinds, & Gadgets Forum' started by 1simplemann, Oct 7, 2017.

  1. Tdawg5664

    Tdawg5664 Refuge Member

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    We recently bought a 17 ft. flatbottom alumaweld with a 90/65 mercury jet on it. The boat will do 35-40 up the river and run in about 1 inch of water. You can look over the side of the boat and see that you are riding on top of the water and that there is zero boat in the water.
     
  2. take'm

    take'm Elite Refuge Member

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    Had a tunnel with a jet years ago(family) at the cabin on the upper Mississippi(like way north at the head water area) all rocks and shallow. worked great! Never had problems with grass or crud while running, but try to take off while in a big grass mat or veggies and your cleaning the grate..
    Way better than destroying props,skags and lower units:yes
     
  3. DEADDUX835

    DEADDUX835 Senior Refuge Member

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    I have owned a few prop tunnels and I run shallow rocky rivers in Tennessee.

    My current boat is a 1448 polar kraft .125 with a 25 hp merc 4 stroke. the tunnel is different than most in that it comes to a point at the top. So the first 5" in height of the tunnel is vertical more or less and then it angles in to a peak making a total of around 6-7" in height. Top speed is @ 23

    I have ran up to a 1860 with 70 hp. top speed was 32 mph

    Here is what I have found with prop tunnels in this environment:

    I can run a true 4-6" straight, but in turns or going higher with the motor and it will cavitate. I haven't found a good prop for that small of a motor to keep from cavitating. Also, because the bottom is not consistent I will strike rocks, damage props, and lower units if you go shallower. Usually this happens way up the river in swift current. I run aluminum props and chew them up regularly as the give point.

    Reverse is still good, but you have less control to turn sharp and you need to rev it higher to get water moving. The inadequacies in reverse (for me) are not much of a concern.

    Everything gets caught in the tunnel. So when you run through leaves in autumn, they tend to go through the tunnel to the foot and cover the intake. If you run the boat into buck brush and stop to hunt, you can be certain limbs and stuff under water will try to hold you in place by getting caught. It can be very tough to get out.

    I like running soup mud or grass flats. A water pressure guage is recommended for that for blockage and motor height. In the winter, it will freeze and become useless.

    The prop tunnels being taller than jet tunnels for instance, create a larger area where displacement is lost vs a normal flat bottom or jet tunnel. This means the boat will sit lower in the water at rest in the back end. Also, on plane the tunnel creates an area of suction (Bernouli or Vertouli principle i believe??) that basically creates a drag and speed loss. Look up "venting a tunnel hull" on here or elsewhere to learn more. It's hard to describe and a weird feeling when driving and it breaks free from the vent or air introduced.

    I recommend pods, a fast jackplate, gator glide (or similar) and tilt/ trim.

    I am actually about to change my setup. Because of the length and design of my tunnel, i am going to weld a plate to the front of the tunnel and weld in a vent pipe (again look this up for speed). I am thinking i will break a plate that will bolt inside the length of my tunnel and sit on this plate to convert it to a jet tunnel. So in the summer when fishing rocky creeks, I will run it as a jet tunnel. (That should answer your question). By flipping the plate over for clear deep water trips, it would make the boat bottom like a normal flat bottom boat and i would run a prop. This would be a speed gain, less fuel consumption, faster plane, etc. Removing the plate would be as now and make it a prop tunnel for duck hunting in swamps. A hydraulic jack plate plus a stationary would allow for the difference in motor heights.
     
    Last edited: Oct 20, 2017
  4. 1simplemann

    1simplemann New Member

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    DD 835, thanks for the reply and insight. I was hoping a prop tunnel user would reply. I spoke Mike Watson and another TN area boat builder. Both gave me their feedback and opinions. Truthfully, I think they only using prop because BASS won't let them run a jet. Your experiences give me the answer I'm looking for. Props and Lower units are expensive. The idea does work but I think the more reliable way to go is with a jet. a customer of mine runs a G3 with a 90/60 hp. He loves it. so much so that this spring he is buying a new one. He told me that I will be the 1st guy he calls when he's ready to sell the old one. If anyone else on here has experience with a prop tunnel, I would love to hear more about them.
     
  5. deadeyedick

    deadeyedick Senior Refuge Member

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    Pacific Flyway
    Prop tunnel worked good for me . Jets are slow and clog up easily .
     
  6. 1simplemann

    1simplemann New Member

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    Would you care to elaborate?
     
  7. calling4life

    calling4life Elite Refuge Member

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    Part of the problem is that aluminum boat makers don't seem to care, so you have companies that run a 3' long 4" deep tunnel whether you buy their 12' boat or their 23' boat. They just don't seem to care, so you obviously don't get the performance, and it isn't a prop tunnel issue, it's a manufacturers don't care to put in the time or money to do it right, issue.

    You also, to run very shallow, have to have a severely cupped prop, I've heard of guys going more blades, I can't confirm that they will go as shallow, but severe cup like this, will hurt top end speed. More motor out of the water equaling less drag works to a point, we're going beyond that point for a specific purpose.

    Another issue, I haven't seen a jackplate that power adjusts more than 6", which, is why, like you said, you may hear of people stacking jackplates, but that may create other issues, leverage issues, weight issues, etc...

    I got interested in this, what I did, was looked at who did it right, namely, the $40k-$150k ocean boats, something like a Majek Redfish line, known to run with the SKEG above the bottom of the boat, now you aren't destroying a lower unit or prop unless that boulder is able to run through the tunnel.

    A prop tunnel done right, skeg above the bottom of the boat, I'd run pods, which means you essentially have hull completely protecting that motor at that point, you'll run in crazy conditions, but you also have to have the bean bag to do it, because if you come off plane, you better have a winch on the front of your boat (which you should).

    I have been looking into this, a big part of why is because I run a Beavertail final attack, the little 8'x44" layout boat, it's a through hull tunnel type design, I doubt by intent, more because they put runners to hold those worthless wheels I've taken off.
    I run a 1998 Evinrude 8hp on it, it's 56lbs or so, heavily cupped prop, I now have my compression plate on it, I run a panther motor bracket, which has a lot of vertical adjustment, but it's manually done. That works for this scenario because I can essentially move the motor vertically several inches just by shifting my weight in this boat when in the water.

    This little turd will run with 60% or so of the prop out of the water, the skeg is at the bottom of the hull, she runs thin, but in this it's dangerous, it's a plastic hull, if I do hit a boulder, my legs are breaking.

    Anyways, it just plays to what I know can be done, you just have to find a boat maker who will do things "right," and you have to understand what you want and what will work. Longer boat can go skinnier width and still draft pretty shallow, like an 1845, shorter boat and you need to go fat, I'm looking at 1270, 1272 kind of territory. Pods mean your rear end doesn't squat, which means you float in less, it also helps kill squat on takeoff, which means you don't have a scenario where you draft 4" of water, but need 14" to takeoff. Transom mount water pickup, for extreme shallow, I'd plan on it.

    For as shallow as my little boat runs, she still handles fine, well done compression plate helps with that, again, it's also a different kind of boat, reverse works fine, you just need to realize you obviously aren't running your prop surface piercing in reverse, so you have to lower your motor, which takes water depth.

    Oh, and as you can imagine, all of this, won't end up making for a cheap setup. Especially since you'll want a .190+ hull running boulders and rocks.
     
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  8. calling4life

    calling4life Elite Refuge Member

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    And an outboard that high, is noisy, my exhaust was out of the water.
     
  9. mister gadwall

    mister gadwall Senior Refuge Member

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    One thing that has not been mentioned much is that the larger boat prop tunnels usually require some distance to get on plane. And sit deep when they are stationary or at idle, and those that have tried them in narrow exposed rocky rivers say that this can be a real issue , especially since you have to be able to get the sunken hull out of a out of the water rack garden and somehow turned and facing a longer "take off slot" that a jet.
     
  10. birdhunter007

    birdhunter007 Elite Refuge Member

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    My last boat was a Lowe 1655TN ( tunnel hull) with a forward console. It was powered by a 110 Johnson with a Jet. It was a fast little boat and I could literally run it inches of water.
    I mostly use my boat in the Columbia and Snake rivers and it was almost perfect for my needs. The 110 really allowed it to get on plane in seconds.

    The plus side... Runs in inches of water..Got me into a lot of areas that a prop wouldn't have taken me. I got tired of replacing props in the previous boat. I hunt mostly gravel areas with skinny water.
    Fast! I could just about keep up with anyone... even with the jet.

    Downside... Loud! The exhaust was completely out of the water. You could here me coming from a mile away.
    Mod V Didn't handle rough water well. In rough water the tunnel would get too much air in it and allow the engine to cavitate. You really had to watch the RPM's .
    Not very good in weeds.

    I now have an 1860 War Eagle with a 150 Jet that I am very happy with. ( No tunnel)


    Lowe 1655TN 002.JPG Lowe 1655TN 019.JPG Lowe 1655TN 023.JPG Lowe 1655TN 026.JPG
     
    Last edited: Oct 29, 2017
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