help with porpoising

Discussion in 'Powerboats' started by wacreator, Feb 6, 2015.

  1. wacreator
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    wacreator Junior Member

    Hey guys

    I have a 17 foot power boat with a 115 hp yamaha outboard.

    It used to be the perfect boat until I added to the transom either side to incorporate duckboards.

    After the transom I made the hull shape curve up four inches over half a metre.

    This was to assist with pushing more water into the centre of the wake for wakeboarding.

    This has worked really well.

    But now I have to have the outboard fully trimmed down to stop porpoising.

    It is frustrating as it does what was required of it but it doesn't allow me to trim the boat anymore.

    Any ideas or solutions would be great.

    Thanks fellas.
     
  2. Kailani
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    Kailani Senior Member

    Post a photo of your transom additions and the boat.
     
  3. wacreator
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    wacreator Junior Member

    What's your email address and I'll send a couple of pics to you.

    I don't know how to post pics on this site.
     
  4. Kailani
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    Kailani Senior Member

  5. wacreator
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    wacreator Junior Member

    Hopefully attached
     

    Attached Files:

  6. wacreator
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    wacreator Junior Member

    Hopefully attached too.
     

    Attached Files:

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    Mein Gott ! At least we now know what happens when you graft on such a monstrosity, I mean addition. I'm not that acquainted with the finer points (or even the coarser ones) of wakeboarding, but I would not have expected a happy ending with what you have down there, so far as general cruising is concerned. But every cloud has a silver lining, I guess your boat can now putter around more efficiently, at low speed.
     
  8. wacreator
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    wacreator Junior Member

    Was the German in case I didn't understand " my god"

    Mr efficiency I guess you didn't read the thread I was asking for assistance not criticism.

    Even constructive criticism is welcome.

    Your comments are just a waste of space.

    :confused:
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    There is your culprit. The hull should be prismatic.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The "answer" is obvious isn't it, take the bloody things off, if you can't "fix" things, by, for example, try fitting wedges between the motor bracket and transom, they are cheap enough, and not hard to install. You will get extra in-trim anyway, if that doesn't help, ditch the add-ons.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    It does look like you made a very good job with those things, pity it does not work the way you hoped.
     
  12. wacreator
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    wacreator Junior Member

    Yeah they ended up coming out really well.

    Do you think it the curve or just the fact I have continued the hull on into a curve.

    I was thinking of a fixed two degree trim tab.

    But thought there may have been a better answer.

    These wedges you speak of what sought of angle should I be trying to ascertain.

    Thanks for the comments.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I have an afterthought on this, you could try spacing them away from the transom by around 12-15mm, and thereby allow air to enter the flow under them, it could help break the flow away from your pods. Might not be practicable, depending on how you have set it up.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Outboard transom wedges are pretty well one size, that I have seen. Just tapered wedge-shaped slabs of aluminium, with holes/slots so you can fit the mount bolts of the engine through them.
     

  15. Kailani
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    Kailani Senior Member

    I don't know how the curve changes the wake for wakeboarding. Never thought about this.

    If a flat section with rocker would make a good enough wake, you could somehow fit in a hinge and a big k-plane with a panel welded on. Trim up for rocker for wakeboarding if that works the way you want and trim down for straight planing surface.
     
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