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

    Hi All,

    This is my first time on a forum so bare with me.I have modified two trailer sailors, one to a power launch using a Frank Pelin 17 ft hull and the second a 16 ft Hartley GTS (Hartley 16 fibre glass version) which I raised the cabin roof and converted to a motorsailor. Both boats I kept the swing keels but both boats only reached hullspeed which at 5 to 6 knots is painfully slow.

    I have purchased another 16ft Quicksilver same as the Hartley 16 fibreglass version.I intend to modify and extend the hull this time. Remove the keel and try and get the hull lines as close as i can to John Atkins Ninigret. Hopefully try and double the hull speed to 12knotswith a 25 hp outoard.

    This will be a lot of work cutting the hull on the keel and chines and modifying the whole aft section.I believe this is the best option and I have the whole of winter to do it.I want a low speed in expensive semi planing 10 to 12knot launch running with small Hp.

    Any suggestions or advice would be welcomed.

    I have seen some boats with a wedge aft to change the buttock angle.I have seen this done but don't know how efficient it is.
     
  2. tunnels

    tunnels Previous Member

    ok simple question first !! where in nz are you ??close to Auckland ??
     
  3. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Mairangi bay.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    A quick perusal of the Ninigret lines shows a hollow waterline forward, which you won't find on that Hartley 16 imo. It is just going to squat like a planing hull on the "hump" even if you "fill in" the lines aft. That would be accentuated running with the chop.
     
  5. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    My plan is to straighten and lower the angle of the hull at the keel to less than 2 degrees and to alter the chine to run aft to almost zero deadrise on the transom.See Gurges 545 on youtube.I have just built a assymetrical cat hull with the same warped V lines and the boat planes with small engine at low speed withou its nose in the air.I agree that the forward sections are not as deep as the Ninigret but will be a shallow V running almost flat from amidships.Thanks for your input.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I would not go hacking into the hull as a first step, I'd be looking at glued-on slabs of foam shaped to your ideas, find a quiet backwater and see what the effect is. But i can't see it behaving any better than an under-powered planing hull that can't get over the hump.
     
  7. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Do you think building a wedge would help break through the hull speed and get over the bow wave.I believe it would keep the nose down a bit.Being a lightly built sailboat with thinner fiberglass than a planing boat i was hoping to get a low speed semi displacement (planing) hull out of the modification.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    A typical semi-displacement boat has the maximum waterline beam aft of the mid point, I don't know where yours stands on that. What kind of waters do you intend to use it in ? Wedges and the like that might lift the stern could turn the boat into a handful running with the waves.
     
  9. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    I see what you mean.It is almost the middle but I am also adding 2ft in length either side of the motor.I have added 2 pictures.The first is the boat the second is a photo shopped image.Without the 2 ft extension.This is a full fiberglass Boat.

    See also Arba 500 on youtube.
     

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  10. daiquiri
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    daiquiri Engineering and Design

    It could work. The only question is - why doing it?
     
  11. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Initial cost of a larger motor and running costs of a big motor. Ninigret figures are perfect and that is a 22ft boat. A 18ft planing boat needs a minimum of a 60hp most run with a 115hp which are very expensive motors.It is a very fine balance between planing and semi planing which makes me nervous and where your advice to modify with styro foam is a good one.I will be using the boat around Auckland harbor, rivers and estuaries.We have pretty protected waters on our doorstep which can get rough in a big blow but I am scared of the sea and will pick the weather and check the forecast.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    He's a Kiwi ! They do funny things ! :D
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    It will be a big job, and no guarantee of of a satisfactory result, you may finish up with a lemon that looks like a dog's breakfast. Gawd, that is a good example of metaphor mixing !
     
  14. Doug Meyer
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    Doug Meyer Amateur Boat Designer

    Thats why I am following as closely as possile the lines of Ninigret and the Nina the LB22 on Bateau.com. You are right though I am a mad Boatie. Picked up the boat good on a good trailer and 20hp Yamaha in good nick with remotes for NZ $3000.00. Pretty cheap for a nice fishing cabin boat for day and the odd overnight.
    The boat in the pictures is the same as mine but not the one I bought.
    Its late going to sleep now gotta work tomorow to fund the project.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    The beam is over 7 feet which is quite wide for a 16 footer, another reason to think it has the job ahead to make the transition you are seeking. I have this vision of a boat running with the nose in the air like a haughty lassie.
     
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