inboard pocket tunnel

Discussion in 'Surface Drives' started by craigttx, Nov 17, 2009.

  1. craigttx
    Joined: Nov 2009
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    Location: rockport tx

    craigttx Junior Member

    I put a pocket tunnel into my 1963 Owens 28' cruiser and I'm wondering about
    which prop would improve performance.
    I ran the boat for the first time today and it ran at 18/19 mph at 4,000rpm
    its a single screw with a 350 inboard.
    the prop is a 13-10, this is what came with it, to my surprise it backs better
    than before.

    I had distributor/motor problem prier and never had a chance to test the boat with its
    regular setup.

    What the speed top speed for a factory 28' Owens and at what rpm?

    Here is pics of the boat and tunnel.
    the tunnel is 10"x 15" wide and 4' long.
     

    Attached Files:

  2. CDK
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    CDK retired engineer

    If you get 4000 rpm at WOT I think you've done it as best as possible. Consider your '63 boat to be an old lady.
     
  3. mark775

    mark775 Guest

    ?????
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Okay . . .

    so, how do you know?

    4,000 RPM sounds like you need a thinner wheel.
     
  5. craigttx
    Joined: Nov 2009
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    Location: rockport tx

    craigttx Junior Member

    I wasnt at WOT that will be reach on the next run, this time was just a quick
    test run.

    The engine was missing badly before I built the tunnel but I did get it to hit
    4600 rpm for a short period in the original configuration.
    (faulty MBI distributor)

    I need to run the boat into 3' of water so I installed the tunnel,now that the
    engine problems have been fixed I would like to know a base line speed and rpm range. I haven't been able to find any info on a single engine Owens.
     
  6. gonzo
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    gonzo Senior Member

    4000RPM is too low. The engine is overloaded. You need a smaller propeller. It may need less pitch, less diameter or both.
     
  7. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    I concur with PAR and Gonzo, I think you are looking to hit 4800-5000 WOT.

    By installing the prop into a tunnel you have changed the flow into the wheel. With the tunnel installed the way you have done, it slows the speed of the wake to the wheel, this results in a lower effective speed of advance (J) and therefore higher torque absorbed (Kq) for a given RPM. In order to reduce torque to get RPM back up in the engine you will need to decrease pitch.
     
  8. craigttx
    Joined: Nov 2009
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    Location: rockport tx

    craigttx Junior Member

    I need to make a few more test runs, that will have to wait until next week.

    As far as higher torque, I didnt here it. the motor went to 4k without lugging.
    The boat did respond to more throttle with a small amounts of lag time and it had slow rudder response but I haven't ran inboards prier to this boat so I can't say if it preforming well.

    4k wasn't WOT, I didn't want to go WOT until the boat has been in the water for a week or so to allow the wood to swell.(painted plywood)

    I would like to find a base line for these kind of boats, a round bilge, semi displacement hull that's over 6k in weight without a tunnel?
    (Cruise speed/rpm and WOT speed at 4/5k rpm?)
     
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Does he really has to subject this old iron cast engine to more that 4000 rpm? The boat is 46 years old and should be treated accordingly. It might fall apart doing more than 19 mph.
     
  10. craigttx
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    Location: rockport tx

    craigttx Junior Member

    She's a old gal or middle age with a new heart.:rolleyes:
    15 hours since the transplant, 13 hours with a faulty distributor.
     
  11. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Missed the part about the heart transplant, thought she only got a 4' ******.
     
  12. craigttx
    Joined: Nov 2009
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    Location: rockport tx

    craigttx Junior Member

    OUCH.

    I have more horses under her skirt than the old cast iron 327 and a new bottom
    to ply the waters.
    The boat came with a log book that was started in 1974 so shes on her third
    heart and undies. The log book didn't included the martini hours.:D
     
  13. Commuter Boats
    Joined: Oct 2006
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    Location: Southeast Alaska

    Commuter Boats Commuter Boats

    Is the photo with the "for sale" sign current?
    For the speeds you're running, rounding the bottom to transom on the sides of your tunnel is not helping. A crisp transition would be beneficial.
     

  14. craigttx
    Joined: Nov 2009
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    Location: rockport tx

    craigttx Junior Member

    Yes the boats is for sale, I might be moving to the other side of the gulf again.
    Florida to Texas now back to Florida again.

    Thanks for the reply's.
     
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