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Thread: tunnel extension?

  1. #1
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    Default tunnel extension?

    I have a 2003 SeaArk 1872JT with the factory jet tunnel. I have the leading edge of the jet foot pretty much lined up with the top of the tunnel and it runs awesome in smooth water and riffles, but when I hit any sort of standing waves (even small ~1 foot waves) it cavitates really badly. I keep reading about transom and tunnel extensions helping with the cavitation issue. What is the best way to attach a tunnel extension to the boat? I've heard people mention UHMW and aluminum. I do not have the ability to weld aluminum myself.

    If anyone has photos of an extension that works well, I'd love to see them.

    Thanks!
    Chris

  2. #2
    Member Akgramps's Avatar
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    How far away from the tunnel is the foot?
    Can you attach a photo of your setup?
    “Nothing worth doing is easy”
    TR

  3. #3
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    Default photo

    Here's a photo of my set up, I should have measured the distance before posting the question. I'll get that soon.

    Thanks!
    Chris
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    Member Akgramps's Avatar
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    It looks to be like you would need to weld a tunnel extension to the transom for best results. Bring it out several inches. It can be extend past the front of the foot, however you will need to cut out a semi-circular opening in the top of the tunnel for the foot to swing. Then install a UHMW flap to cover the gap between the tunnel amd the foot. (you will need some clearence between the tunnel cut-out and the foot 3/8" - 1/2"). W/o the flap water will spray up bigtime, IME.

    I think this would be the best, be carefull to make sure the top of the tunnel extension is paralllel to bottom of the boat or just ever so slightly angled up.

    If you dont want to go thru that much effort, fabricating, visit to a welder, etc, then you could try a piece of aluminum angle bolted to the transom even w/top of the tunnel, and a piece of UHMW bolted to that.
    You would most likely need to get that angle bent at a sheet metal shop as the angle is not 90 degrees. It would be cheaper than buying a 10 foot stick of aluminum angle anyway.

    It looks like the bottom of the boat is nearly flat? If so ventilation/ cavatation in a light chop may be diffucult to overcome.

    In the first picture you can see the tunnel extension and the UHMW bolted to the top. Also note the down hill slant of the tunnel, you wont believe how much grief that downhill slant caused.......................!

    In the second picture you can see my quick experiment with some colored sheet metal, I cut the corners of the tunnel and bent it up some 3/4" and threw that scrap metal on to try it, and what a difference, it was a if I gained power steering and noe the boat goes where I point it. This also allowed me to raise the motor one set of holes, a very good thing.....

    I have effected a permanet fix and all is in order, the bottom line is I figured it out on my own, so dont be afraid to experiment......Every boat can be a little diffrent............good luck
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    “Nothing worth doing is easy”
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    Default Thanks!

    Thanks for the insite, definitely helpful!

  6. #6

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    http://forums.outdoorsdirectory.com/...ad.php?t=39139


    if you look down in that thread you can see what i did to my boat and works really well. some boats just dont like some waves

  7. #7
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    Like Akgramps said, just a little extension around the back of the tunnel is most likely all that is needed. Add a little UHMW then some wings on the side of the jetfoot like Glen Wooldridge suggests to draw in more h2o, and it should be a pretty good fix.

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