Modify Sailboat to Semi planing

Discussion in 'Boat Design' started by Doug Meyer, Jun 14, 2013.

  1. Doug Meyer
    Joined: Jun 2013
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    Doug Meyer Amateur Boat Designer

    This was my previous one where I had modified the Cabin top with a 15hp 2 stroke.Running nose in the air and getting nowhere.It will take plywood from max beam aft to make any difference.The second picture (blue boat) is my first one running a 8hp 4 stroke.both are trailer sailors.The one I have now is the same as the white one. 16ft Hartley/Quicksilver.The blue one had a slightly straighter run aft.
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You are certainly not a man to give up easily, and I have no doubt you will complete any alterations to a high standard, but I fear it will be to little avail. Be happy to be proven wrong though !
     
  3. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    I am obviously missing something (maybe a few bolts in my head) I don't understand the the term hollow waterline forward.This boat has a shallow V as I understand.About a third the boat length from the bow.

    So you are saying no matter water buttock lines I change aft of max beam the performance will not be better than hull speed?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    The hollow refers to the concave forward waterline shape in the plan view. I could not assign a probability that you will exceed "hull speed", buy it seems like an uphill battle to me. I agree with PAR that testing a model (in a swimming pool maybe) could give some useful clues about likelihood of success.
     
  5. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Thanks I am not arguing with you just trying to understand the basics forces of water and how other boats can do it.

    The forward section displaces water either side of the keel which runs aft and outward Generating the lift are the aft flat sections which the boat rides on the boat rocks back onto these sections and the forward bow clears the water depending on how much pressure the aft sections exert and speed and angle of attack.This is how I understand it as a layman.

    The Lobster Boat rides like this see B&B Yachts Outer Banks 20ft runs with a 25hp
    If I make my aft sections the same and keep the boat light which it is what am I missing you guys are professionals and are skeptic which makes me nervous about tackling this job.I have built models with a box keel that I could add on it went the same with it and without it so power setup wasn't to scale.The other issue is time I need this boat ready by end November I missed the last 3 fishing seasons building boats want the right boat ready.Thanks for you contributions Mr Eff and all others.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yes, Doug, you are missing something, which are the subtle difference between a sailboat that can plane and the typical powerboat shapes, that also can plane. A sailboat usually planes on it's midship sections, dragging it's up swept aft sections along for the ride. Of course some are much better suited than others, but generally you have a S/L limit and you just can't get past it. Powerboats plane off on their flat aft surfaces, carrying the midship and forward section clear of the water (for the most part, depending on S/L).

    Box keels will permit a tad bit more speed, but these too are S/L limited - just not enough bearing area aft. I have never seen a box keel design of any configuration get past the low 20 MPH range, with reasonable power or reversed deadrise aft (which is also S/L limited).

    You can reshape the bottom of that boat, but you'll learn a lot by watching her wave train, as a model is pulled the length of a pool at various speeds. You can video these "tests" and go back to see where you'll run into the "wall" and can appropriately size you engine, for the speeds you can expect. This also permits bottom shape adjustments, chine verses round bilge, etc. for very little effort and cost, again to evaluate the "value" these modifications might offer the full size version.

    It's your call, cardboard and some tape or plywood and some epoxy.
     
  7. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    OK, finally the penny has dropped (it is clear my title must remain Amateur) thank you Mr EFF for the sound advice.I didn't know that's where it planed I thought modifying it from amidships aft and extending it would be the surface it would plane on. I will take your advice and build some models and drag them to see where I can that stern wave furthest from the boat.
    Anybody out there got the offsets for a Hartley 16 to save me crawling under this one to get the lines.
     
  8. tomas
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    tomas Senior Member

    Some people come here looking for advice and input, but get upset and defensive when they don't hear what they want to hear.

    Doug, you have an open-minded attitude and willingness to listen and learn.
    I'm learning from your project.

    I wish you success. :)
     
  9. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Thank you, Its hard when you have gone round in circles for months and then made a decision only to be told its a long shot and has distinct possibilities of not working.
    It is better though knowing now than doing all that work and ending up with a lemon and for this I am grateful for all the members input.
     
  10. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Anybody's thoughts on this option, just want to get over the bow wave. Its a much easier mod than previously planned.
     

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  11. tunnels

    tunnels Previous Member

    I had a 22 foot Paul Whiting trailer sailor that used to plane quite comfortably with a 25 hp mercury on the back and up set a few power boaties coming home after spending a weekend sailing . Used to call into a sheltered place drop the mast and fold up and pack away everything have dinner and then head for home planning all the way up the Auckland harbour to the te atatu boat ramp passing slower launch's all the way . Raised a few eyebrows that's for sure . the hull had a really nice shape aft and lent its self to be able to plane and with a big heavy cast iron swing keel was comfortable to ride in !!:)
     
  12. tunnels

    tunnels Previous Member

    Just one thing you need to look at seriously !!
    what makes a boat plane along the surface of the water !! if you are thinking seriously of being a designer of any sort this should be a really easy question for you to answer !! :confused:
    If you cant answer it then take up growing flowers or change your interests !!:eek:
     
  13. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Sounds good I think I have the wrong shaped hull for what i want to do anyway.
     
  14. tunnels

    tunnels Previous Member

    And that only took a few minute to realise !!
    so if you wanted to make it plane what do you need to change ?
    and from where would you start to make the modifications ??
    Where and what part of the hull will it sit on when its planning ??
    now that wont take to much thinking about I hope !!:idea:
     

  15. messabout
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    messabout Senior Member

    I second Tomas compliments about you open mindedness.

    Sure enough a lot of people come her to solicit advice and perhaps helpful comments. A painful number of them have their minds made up before they get here, and no amount of reasoning will penetrate their armor plated skulls.
     
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