Second forestay chainplate on A-cat hull

Discussion in 'Multihulls' started by revintage, Jun 25, 2019.

  1. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Cut an opening in the A-cat hull, to be used as center hull on my Windknife trimaran. My idea is to add a second forestay chainplate on the opposite side of the hull.

    I had hoped for the hull sides to be reinforced on both sides, but they wheren´t. Hull is made from epoxy/grp/foam sandwich. Did an ugly simple sketch on a possible solution. Question is if the foam needs to be removed and replaced by injected epoxy in the actual area?

    Hopefully there is a better and simpler solution to this?

    IMG_3967.JPG IMG_3966.JPG IMG_3959 (redigerad).JPG skiss.png
     
  2. patzefran
    Joined: Feb 2011
    Posts: 180
    Likes: 10, Points: 18, Legacy Rep: 10
    Location: france

    patzefran patzefran

    You need to reinforce like the other side !
     
  3. trip the light fandango
    Joined: Apr 2018
    Posts: 278
    Likes: 48, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    A spreader plate the shape of the deck in aluminium, glass or stainless as well as the new replica of the original chain plate set up perhaps. Strengthen the deck hull join longitudinally internally a little while your there, . Not sure about the through bolts ? but I'm no expert. regards
     
  4. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    The force from a 90 degree bridle will result in about the same vertical force in the hull sides as the original A-cats forestays. There will also be an inward force of the same magnitude, thus there need to be something like the bolts or a rod between the hull sides to take up the compression.
    Don´t want to open up the structure. Drilled holes for the new chainplate in the outer layer and removed the ca 3-4mm hard foam from the sandwich in the area surrounding the new chainplate and will inject West Six-10 in the cavity. This together with a G10 plate with a few layers of glassfiber mat upon at the inside going up under the deck, will make the buildup simpler.
    Idea: If using a thick wall alu tube instead of the upper bar, it makes if possible to arrange the bottom of the bridle going through the hull/chainplate. See simple sketch.

    detaljchainplate2.png
     
    Last edited: Jun 26, 2019
  5. trip the light fandango
    Joined: Apr 2018
    Posts: 278
    Likes: 48, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    From your diagram it looks like the top through bolt is below the widest point so compression there is unsupported. Oldmulti posts would probably suggest making a fibreglasss foam sandwich transverse deck beam glassed underneath to manage the load, . I'm working on off the beach cat hulls too and have reached the conclusion that access holes have to be made in the deck to be confident that the glassing is done properly. Before replacing the "divet" I'll reinforce the hole
     
  6. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Hi, what is divet? Not sure what you mean:
    Access to the inside of the chainplate area is very limited, don´t think I will be able do anything more complicated than what I described earlier.
    The dyneema is supposed to be a sling, with its ends meeting at the forestay.

    skiss.png
     
  7. trip the light fandango
    Joined: Apr 2018
    Posts: 278
    Likes: 48, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    Sorry just being a bit silly , it's a golfing term , it refers to the lump of grass taken out with a golf swing. There isn't much room in the fine bow but as long as the hull deck join isn't cut and is added to a little, the overall strength and look shouldn't be affected.. How much extra load do you expect to add to the area above its original design specs is the riding question as to how good an answer can be I think.. Nice diagram by the way, very neat. Aluminium tube is mentioned on Oldmultis thread for through bolts on masts. Where the lyros plastic bends is the point I was concerned with.
     
  8. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

  9. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Another, but a litte more elaborate solution. Inside width is in the ballbark of 150mm/6".

    detaljchainplate3.png
     
  10. TeddyDiver
    Joined: Dec 2007
    Posts: 2,552
    Likes: 112, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Looks a bit complicated solution. Why not new composite chainplates on both sides? Add a bulkhead inside the hull and laminate carbon fiber chainplates..
     
  11. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    So you recommend to rip up the hull and really complicate things:D? Note, the intention is to do the opposite. I’d like ideas of a simpler solution, not more complicated. My sketches are just results of crazy brainstorming, nothing to take to serious. This one is the latest one, with a dyneema internal bridle, unfortunately leakage would be a problem if this one should be used ;-) .

    detaljchainplate3.png
     
  12. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Realized the above was a total overkill. Will instead bolt an eyebolt directly in the fore deck, eventually adding an alu bar lengthwise. The deck has a much fatter carbon fiber reinforced laminate than the hull. With G10 and alu to spread the load over a bigger area this will surely work. I have calculated load to be max 200kg.

    detaljchainplate9.png öglebult.jpg däckskena.jpg
     
  13. trip the light fandango
    Joined: Apr 2018
    Posts: 278
    Likes: 48, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    That idea of epoxying dyneema on SA is a light and strong solution. I think that the hull deck join with say 800mm lengths of dyneema and perhaps 2 lengths of dyneema each side as triangular chainplates , the loops can protrude like pad eyes, and internal spreaders made the same way, could be a good. interesting build, good luck
     
  14. Doug Halsey
    Joined: Feb 2007
    Posts: 393
    Likes: 102, Points: 53, Legacy Rep: 160
    Location: California, USA

    Doug Halsey Senior Member

    Sorry, but what does "SA" stand for?
     

  15. revintage
    Joined: Nov 2016
    Posts: 207
    Likes: 39, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    SA= Sailing Anarchy.
    Got loads of info there, in my thread about my chainplate problem/solution.

    About dyneema and epoxy, this is interesting. Must try! Still hasn’t decided, but some kind of dyneema bridle is the road I am going.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.