Sunday, July 18, 2010

Above image is an assembly of the cad models i have been using to size and design components. The layout is not 100% of what i intend to use, but it has been extremely helpful in locating important points and dimensions. It has also allowed me to investigate the size and shape of the side tanks so that i can ensure it meets the class rules as well as provides enough space in the side tank to fit the spinnaker chute.

This is the centreboard case i intend to use, it allows the centreboard to have 200mm of movement fore and aft so that I can tune the centreboard position to the new rig and rig position. The adjustability comes from using different cover plates, both of the these plates on top and bottom are held together with a threaded rod. The cover plates are made custom for each centreboard position that is needed.

Above is an image of the cover plate in place, this top surface will be flush with the top skin on the false floor.

This is the centreboard case in the vacuum bag. It was constructed by shaping a piece of extruded polystyrene foam called "ISOBOARD", which is normally used for insulation. This was then laminated over with 4 layers of 200gsm glass cloth on the -+ 45 deg so that the cloth would pull into the tight corners. It was decided that 4 layers should ensure that the case is water tight.


  1. Hi Adam... a few of questions re the centrecase...
    1. the text says glass is being used but in the picture it looks like carbon
    2. what material are you using for the top/bottom plates
    3. did you glass the inside of the case

    I am also building a centre case to allow flexibility for tuning but it screwed up so am back to square keen to hear more on what you have done. Thanks. Its going to be messy digging it out of the hull.

  2. Hi Paul,

    yes i have used glass in the centreboard case, but i used a black pigment in the resin, what you can see in the image is all the excess black resin soaking into the breather fabric after flowing through the peel ply.

    The top and bottom plates will be approximatly 18mm plastic. I have some material at home which is a hard, high density plastic sheet. If i have difficulty cutting and shaping this i was going to look at using nylon or any other type of plastic, due to the low friction from the plastic when raising and lowering the centreboard. I believe you can source cheap nylon by cutting up old chopping boards or possibly finding some in $2 stores, although they tend to be pretty thin and nylon can be difficult to make a neat finish. One option we looked at was casting a bottom plate, using some form of casting resin.

    I only used glass in the centreboard case, as all of the strength for my case will be made when it is laminated in / to the hull. I'll try to include a diagram of how i intend to glue it in shortly. Hope this helps.


  3. also i forgot to mention, i made a male plug with the polystyrene foam using a router, then laminated the outside, with the plan to "melt out the foam core with acetone so that i end up with a fibreglass shell for the centrecase.
    Cheers Adam

  4. Thanks Adam. very interested in to see how you plan to glue it in. I am thinking I might make the whole case out of ply with the plates out of chopping boards. My skills with foam and glass are making this kind of construction a challenge. Paul.


  5. I agree, i think plywood is a pretty good choice, i certainly looked at using just a 3mm ply to make a box, then glue strips of the 3mm ply onto the inside of the box to make the flange for the plates to sit on.

    The only reason i'm not planing on using chopping boards at this stage is because i was after a thicker bottom plate to help distribute the point loading on the centreboard as i will be using a carbon fibre foam sandwich centreboard and feel that a thin plate might help lead to the centreboard failing.