Semi displacement conversion to outboards

Discussion in 'Powerboats' started by wildsideboats, Mar 3, 2019.

  1. fallguy
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    fallguy Senior Member

    So, they are gonna pound you to death with the low dr at the transom?
     
  2. DCockey
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    DCockey Senior Member

    If "planing rails" are strips which run along the turn of the bilge then they are common on Maine lobster boat type hulls. The builders and owners of the boats are convinced they are worthwhile.

    The Sisu 22 is a popular design which has been around for over 40 years. Originally inboard powered they now have an outboard on a bracket. The design was modified in the 1980's or so with built in spray rails which improve high speed behavior. Eastern currently builds the Sisu 22 though I believe there are other molds around. https://www.easternboats.com/22-sisu

    https://www.soundingsonline.com/boats/sisu-22
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Not really, they are not going fast enough to take ballistic trajectories off large swells, and have sufficient boat length to handle shorter chop without exposing the flattish aft bottom.
     
  4. DCockey
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    DCockey Senior Member

    If you run fast enough into large enough waves they will pound. Solution is to throttle back. That's the tradeoff for the low resistance and minimal hump. No single design does everything well.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    If they were not original to it, you would wonder why. I sense he is looking for more speed, and thinks these rails might go toward delivering it. At its current cruise speed, I'd doubt they'd be beneficial, you don't get much lift frim such things at modest speeds, unless the boat is light. Top speed might be up a little, but top speed should not dictate much.
     
    Last edited: Mar 4, 2019
  6. DCockey
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    DCockey Senior Member

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Knocking down spray helps gain a little speed, but he speaks of "full length planing rails". At 20 mph not going to do much, and pretty redundant toward the flat stern.
     
  8. DCockey
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    DCockey Senior Member

    I wonder if he has actually seen the boat. As I said in my note above the design already has full length integral spray rails / chines.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    I noticed the bow area, couldn't see what else was there further back, I would not be going down the track of putting any more on it. I think if not happy to cruise at 20 mph, go to a planing hull. you can't really stretch these types of boats into speed machines, not sensibly anyway. And the outboard conversion option needs an existing, successful example as a template, or too risky. Why be the guinea-pig !
     
    fallguy likes this.
  10. wildsideboats
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    wildsideboats Junior Member

    All good input and much appreciated . Yes this post is to see if anybody has attempted this or similar conversion . I am a fiberglass boat builder / restorer . I do ovvn this boat and plan to use it for fishing / diving / cruising . High speed is not my greatest concern hovvever I vvouold like to cruise at 18 to 20 kts. I have installed these lift/spray strakes on tvvo similar hulls and it made a remarkable improvement on both. Im in the process of removing the balsa core from the hull, Ive reached the engine room forvvard bulkhead and had a " I vvonder " moment.... I vvonder if anybody has ever put outboards on one of these ? Because Im at the stage of either rebuilding the engine compartment for an IB or use that space for something more creative . Just a shot in the dark, makes for interesting conversation if nothing else...
     

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  11. fallguy
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    fallguy Senior Member

    Isn't locating the strake difficult, when the waterline is changing? Ot do you jist build it long and down below the WL aft to above the WL forward and guess some?
     
  12. DCockey
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    DCockey Senior Member

    Based on the photo of the corner of the transom the inverted extending from turn of the bilge is very similar to the Sisu 22.

    Is the black rubber extrusion what you are planning to use as the lift/spray strake? Will you follow the existing chine with it?

    What is the "Anne Elise"?
     

  13. wildsideboats
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    wildsideboats Junior Member

    Yes, basically doubling the vvidth of the lifting strake. Photo of boat is just a boat that looks similar to vvhat this boat vvouold look like vvith OBs.
     
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