Windknife trifoiler build

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

  1. revintage
    Joined: Nov 2016
    Posts: 93
    Likes: 12, Points: 8, Legacy Rep: 10
    Location: Sweden

    revintage Junior 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
    Posts: 93
    Likes: 12, Points: 8, Legacy Rep: 10
    Location: Sweden

    revintage Junior 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.

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    Last edited: Dec 9, 2018
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  3. revintage
    Joined: Nov 2016
    Posts: 93
    Likes: 12, Points: 8, Legacy Rep: 10
    Location: Sweden

    revintage Junior 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
    Joined: Nov 2016
    Posts: 93
    Likes: 12, Points: 8, Legacy Rep: 10
    Location: Sweden

    revintage Junior 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.
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  5. revintage
    Joined: Nov 2016
    Posts: 93
    Likes: 12, Points: 8, Legacy Rep: 10
    Location: Sweden

    revintage Junior 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
     
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