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Thread: Tunnel Hull Issues

  1. #1

    Default Tunnel Hull Issues

    I have a lowe 16 foot tunnel hull. Its powered by a 2012 50hp etec jet. My main problem is getting on step. My motor raps out at 5200 rpms and to be on step I have to be running at 4900-5000 rpms . This is empty too just me and a six gallon can of gas. In very shallow water it planes out nice but if I back down on the throttle i'm stuck. My tunnel is 6 inches deep, 8 inches wide and 48 inches long. Ive noticed that when on step the hull planes out at the jet foot which is level with the top of the tunnel. That means that six inches of boat for 48 inches is still in the water. But in very shallow water the tunnel performs well and the entire boat is planed out. I know the motor can push this little boat just fine. And when comparing to a 17' lund flat bottom with a 30 horse jet the 17' is much more responsive and faster than mine. Also if I take a sharp turn on the river the boat cavitates and looses its step. I believe my problem is my tunnel is just too large. So my options are have the tunnel sealed off and make the boat a flat bottom or have the tunnel reduced to a smaller size. What do you guys think? Smaller tunnel or flat bottom? What would be a good tunnel size and who is a good aluminum welder that could do the work? Thanks Sam

  2. #2
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    Have you checked the wear on the impeller and liner ?

  3. #3

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    Yes , everything on the motor is good. It's been this way since the motor was new

  4. #4
    Member Dirtofak's Avatar
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    Take it off the trailer.

    That boat should fly. If you are cavatating you might look at the other tunnel designs out there. I would think 30 MPH or better on a lake.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
    Bill Hicks

  5. #5

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    Your tunnel is designed for a prop . It should only be about 2.5 " deep its an old roughneck isnt it? Bad design, cut that thing out and replace it with a modern tunnel .or if thats out of the question cuzz its expensive fill it in with sone wood or somthing your loose alot of flotation with a 6" deep tunnel

  6. #6
    Member gutleap's Avatar
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    I second the thought your current tunnel is too deep for a jet foot. The proper depth of a tunnel should equal the drop from the front of your jet foot to the back of the jet foot. Most are around 3 inches.

  7. #7

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    Apparently there's a whole equation for figuring out what the actual depth should be its on the californial jet website. . Theres gotta be a cheap way to fill it in .. It will make your boat way better you can probaly buy a tunnel from somewere and bolt it on with alot of narine silicone and your boat would be a whole new beast like you wouldnt believe

  8. #8

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    Karolds Welding in fairbanks is going to put a new tunnel in for $575. The new tunnel will be 30 inches long, 3 inches deep and 9 inches wide at the top and 12 inches wide at the bottom.

  9. #9
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    I learned the hard way on my Alumicraft, bought it new and it was a prop tunnel that the dealership welded a plate in tunnel to adapt to Jet (or someone did). Only problem they left the above area open and when stopped it would fill up with water and took more to plane out. I filled it in with spray foam and it improved considerably. Also not sure if you have had impeller out, check sleave to impeller clearance. I also learned hard way on this, there is factory clearance that if you have to much will cause engine to over rev without suffiecent power. I believe the clearance on my Mercury unit was 50000's but check spec's to be sure. Also do you have Spontoons on back of boat (maybe called something different). I had these on my boat and after hitting a few rocks and cracked welds they would also fill up with water and slow boat down. Welds were bad design. I had skid plates put on them to keep rocks from breaking welds.

  10. #10
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    your tunnel is for a prop it needs to be closer to be 2.5-3 inches high at the back and 10 to 12 inches long it also needs to fan out and taper down to the front of the boat to pull the water on corners. it needs to run out past the bottom of the boat and as close to the bottom of your jet foot as possible to keep from spraying up the back of the boat. it should only take about two hours to install at the most on your boat. I have put lots of these in the older boats and they work great. my old Quachita has a 5' bottom and is 20' with a 90 horse and jet and it will run over ankle deep water gets right up on step call me at 388 -8525 or send me a message if you need help with it TJ

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