Jet tunnel hull vs. no tunnel

Discussion in 'Boating' started by great pappy cat, Feb 25, 2008.

  1. great pappy cat

    great pappy cat Active Member

    Messages:
    728
    State:
    P.A
    I was wandering what the disadvantages of a jet tunnel hull were.As far as I know the advantages are to lift the motor intake above the hull to prevent collision.To provide a steady flow of water into the intake.And to gain a couple inches of draft on plane.Im lookin at a sea ark 2072 jet tunnel with floatation pods and a 115/80 yamaha 4st outboard.Im more concerned with draft on drift than on plane. Would a 3 deg. hull draft less on drift because it displaces more water? Would the float pods offsett the difference? Is there a difference in wich can jump on plane quicker? Would the tunnel cavitate more in a moderate chop? Which would handle better?Im so confused I spoke to alot of people about this and got a mixed bag of answers??:eek:oooh:
     
  2. Katmandeux

    Katmandeux New Member

    Messages:
    1,618
    State:
    Checotah, Oklahoma
    I don't have answers to all of your questions, but I'll share a couple of observations, based on my experiences with my 1652MVT SeaArk.

    Draft on drift, as you call it, is a significant issue, for several reasons, the first being the tunnel. The tunnel gives away a lot of buoyancy, right where it's needed most. I can't say how much the pods will offset this, as they weren't available at the time I bought mine.

    The second reason is the engine, which for jets is, of necessity, a lot larger and heavier than a comparable propped motor. Mine, for instance, is a 60/45 2 cycle...if I were buying today, and bought a 4 cycle, the weight penalty would be even greater.

    Finally, because the engine is larger, it requires more fuel capacity for the same range, ergo, more weight.

    The only way to compensate for all of this is with pods, which btw, add weight just where you'd rather not have it, and weight distribution. I have located my battery, fuel tanks, and helm in the front half of the boat, and that has helped, but the boat still drafts more than I would like, while dead in the water. It's the price you pay for a jet, and that reduced draft while on plane. I think all of us that run them cross our fingers every time we cross skinny water, and hope the engine doesn't burp, or that we don't suck up a plastic bag.

    If you'll look at the Lowe 1655TN, you'll notice how they have approached the "problem". The bottom is wider, the fuel tanks are mounted amidships, and the helm is well forward.
     

  3. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    If you read SeaArk's website, their tunnel hulls are designed primarily for prop driven motors, allowing you to use a 15" shaft rather than a 20" shaft motor, which is a nice (and much cheaper, and more efficiant) alternative for a shallow water drive.
     
  4. Wabash River Bear

    Wabash River Bear New Member

    Messages:
    3,019
    State:
    Indiana
    I need to correct something here, the transom is raised the depth of the tunnel, still using a 20" shaft, prop driven motor, not a 15" shaft.
     
  5. loanwizard

    loanwizard Well-Known Member

    Messages:
    3,297
    State:
    Coshocton,
    I have a 2072 pro with a 115/80 on it. I have the 15 degree hull and it will handle any water I'll ever put her in (I'll let you know for sure when I get back from the James next Friday)

    Pods are a definite consideration as I plan to get some for mine. You do NOT need a tunnel hull. My jet hangs maybe 1/2 to 3/4 of an inch below the bottom of the boat. I will say get as big a motor as you can afford. I am already planning to upgrade to the 22 Alaskan Predator with the Merc sportjet. On SeaArks 20 footers the 115/80 is the absolute minimum I would ever go.

    Remember you can't start a jet in 6 inches of water, you best be on plane by the time you hit the shallows. That is what is exhilarating, going over inches deep water at FULL THROTTLE!!!!!!!