Windknife trifoiler build

Discussion in 'Multihulls' started by revintage, Dec 7, 2018.

  1. revintage
    Joined: Nov 2016
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    revintage Senior Member

    This is the plan of my Windknife trifoiler, in the spirit of the Hydroptere prototype and Doug Halsey´s Broomstick, I am building to be ready 2021. It would have been nice if I could have built it this winter, but I have two other projects to finish before.

    I have got tremendous help from Doug Halsey(thanks!) to navigate through the hydrofoil mine field. We are still discussing the final shape of the hydrofoils, that will be built around aluminium profiles from www.windknife.com.

    I have now collected most of the parts, including the components for the foils. It is over square at 5.5x6m and built around a very light GRP A-class hull with an aluminium mast and an 8 year old Glen Ashby A-class sail, total weight just below 100kg. The rear beam is 70x2mm round alu tubing with water stays and the main beam is supposed to be built with the same 100x2mm alu tubing I have used on my two Frankencat Nacras. The amas are made from a short epoxy custom windsurfing board, that I have cut in half. All ropes for stabilizing the platform and also standing rigging will be 4mm Liros X-Pro Static. As this is a Frankenfoil low cost build my budget is max 1500USD ex labour.

    A few days ago I bought a broken F18 Goodall mast with the top 6meters completely undamaged. The spreader, diamond and mast top fittings will go to my aluminium mast, except for the hounds fitting that I bought from Fiberfoam, where I also bought the cup and cone for the mast base. Even if I dump the F18 tube, the fittings are worth a lot more than I spent on the broken mast. Got the idea to use the C152 section mast tube as main beam even if it has a 2kg weight penalty against the 100x2mm tubing I intended to use. The profile almost fits the hull, when lying the normal way with the rounded nose forward. But placing the section upended with the nose downwards, it would be less prone to downward bending. As I intend to use water stays, it will probably not be an issue, even with the nose forward where air resistance will also be lower. I would really like to have some comments about the latter subject.

    More info about Windknife and hydrofoils and on my "Frankenfoil Sverige" FB:
    Log into Facebook | Facebook https://www.facebook.com/profile.php?id=2160774603967026&ref=br_rs

    Windkniferiggvang2.png
     
    Last edited: Dec 8, 2018
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  2. revintage
    Joined: Nov 2016
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    revintage Senior Member

    This is the A-class beam pocket initially made for a 150x60mm front beam. The C152 mast section, at 152x76, with same length but fatter, will be easy to adapt. Rear beam pocket is 70mm round.

    beampocket.jpg
     
    Last edited: Dec 9, 2018
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  3. revintage
    Joined: Nov 2016
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    revintage Senior Member

    These are the windsurfer board halves before I flat sanded the insides.Have got valuable feedback from Waynemarlow, on how to build up the inner, completely flat sides.
    A0A3FE5A-287C-4C70-A9D7-EF4484C72E9D.jpeg
     
    Last edited: Dec 9, 2018
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  4. revintage
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    revintage Senior Member

    Unfortunately the budget does not allow for a carbonfiber mast. Will start with a cut down old Sailspar Tornado mast, that has a surprising resemblence of todays A-class mast bend characteristics. The image shows the sail hoisted in my Frankencat1 F18 mast.

    No need for comments, as my intention is to use this forum as a blog for the Windknife build.
    0572E4E3-8D18-41F7-A5E5-28E0D411A93A.jpeg
     
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  5. revintage
    Joined: Nov 2016
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    revintage Senior Member

    As this is a budget build there will be no full carbon fiber foils. Will build it with The Foil Nose from www.windknife.com, Paulownia filling and a combination of 0.5/1.0mm G10 and 0.6mm high gloss carbon fiber sheets.

    At the moment I have landed in a 168mm straight foil starting with the 45mm symmetric NACA 0012 Windknife FN followed by a flat bottom section with NACA 0012 height coordinates. Close to 2512 but with 2.14% camber at 52.8% according to Javafoil.

    Weight will be 2kg/m.

    With my method it is possible to taper the foil from 150 to 275mm chord, from 18 to 33mm thickness. Still thinking about it, not knowing if it will have any great benefits.......

    Surely the foil can be refined, but this is where my knowledge ends.

    0012flat.png foilnosedim.jpg
     
  6. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Intend to cut down the A-class sail and instead add a 2.5 sqm jib as CoE needs to be lowered ca 1 m. Was first into cutting off the lowest panel, but Grant Piggott recommended me to cut the two top panels instead(blue batten). A little worried as the square top will then be almost 1,2 m. This will shorten the luff from 8.5m to 6,6m(1.9 m) and reduce sail area with 1.9 sqm.

    If cutting the bottom panel instead, the area will be reduced by 2sqm, when only 1.1 m is cut off.

    Any preferences?

    IMG_2164.JPG topcut.jpg bottomcut.jpg
     
    Last edited: Feb 16, 2019
  7. revintage
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    revintage Senior Member

    Decided to cut at the bottom like in the photo edited image. Cutting just under the first batten pocket removes 2sqm and also makes it possible to try boomless with a stiffer batten.
    cutmontageSS.png
     
  8. revintage
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    revintage Senior Member

    Just began to cut down the main. The area at the end of the first batten pocket was heavily delaminated and damaged under multi layers of tape. It felt good to remove it by moving the leech 7cm further in.

    Two options of the rig, as shown or moving the forestay to the bow and run a full 4.7sqm 49er jib instead of the radically cut down at 2.5sqm. The latter will be just OK when the winds blow, though.

    IMG_2177.JPG rigfoil.jpg SEGEL.png
     
  9. revintage
    Joined: Nov 2016
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    revintage Senior Member

    The old patches are reused and taped.
    Just some minor taping needed, before going to the sail loft to get the seams and the tack and clew eyelets done. IMG_2205.jpg
     
  10. revintage
    Joined: Nov 2016
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    revintage Senior Member

    The main is back from the sail loft and the broken off F18 mast was pickef up the same day. The 6m long top piece will be stripped of its fittings. The tube will probably be used as main beam and the fittings will be reused on the mast. Checked the lower short stump in the beam pocket of the center hull and it was a close to perfect match. 350B12B6-BB5F-46EC-A4DF-B7D951578231.jpeg 6DEE1962-9E42-4C65-B46C-B2056658D621.jpeg
     
  11. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Reality checked my chosen beam dimensions wrt to wall thickness and diameter and realized I had chosen to heavy tubes, dumped both the 100x2mm and F18 mast tube. Compared them and other commercially available dimensions in Sweden to Broomstick beams and opted for dimensions that where 1,2x stronger wrt torsion and bend. Will use 90x2mm for the main and 75x1.5mm for the rear beam. This also allows me to use 75&90mm standard PVC tube fittings together with connection tubes between main and rear beam. As I wasn´t happy with the shroud bridle and using a line outside of the trampoline this is now solved. Have also solved the waterstayarrangement: Main beam waterstays on small foiling tri https://www.boatdesign.net/threads/main-beam-waterstays-on-small-foiling-tri.62018/ Weight will still be kept under 100kg.


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    Last edited: Apr 1, 2019
  12. patzefran
    Joined: Feb 2011
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    patzefran patzefran

    From my experience on two trimarans, Strike 15 and Strike 20, don't use Dynema even pre stretched or the best grade. It stretch at each sailing. Now I use Vectran on both ad even on the dolphin Striker of my Paper Tiger Catamaran. After several years experience, Vectran don't stretch !
     
  13. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Liros D-Pro doesn’t creep or lengthens in our country;). Will keep control of tension with my Spinlock Rig Sense until it settles.
     
  14. patzefran
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    patzefran patzefran

    Good luck !
     

  15. revintage
    Joined: Nov 2016
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    revintage Senior Member

    Change of plans! 75x1.5mm tubing is not available in Sweden. Will instead go for 70x2mm for the rear tubes that actually is somewhat stiffer both wrt bend and torsion.
    To make them fit I will lathe 75x2.5mm sleeves to fit in the 75mm fittings. This will increase weight by 2kg, but still under 100kg.

    Got the idea to relocate the horizontal stabilizing lines to the ends of the main beam, don´t know if it will make any difference.

    56685801_10215797980916088_5440969896055799808_n.jpg
     
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