bench supports

Discussion in 'Boat Design' started by Tungsten, Nov 17, 2012.

  1. Tungsten
    Joined: Nov 2011
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    Location: Canada

    Tungsten Senior Member

    Here's a pic of what i'm upto.
    [​IMG]

    This is 1/4"6mm foam glassed both sides.This will support the rowers bench which will fit between the supports and rest on say about 2" of the top part.

    I would assume the horizontal peace should sit on top of the vertical when glued together.My plan was to fillet the underside then tape and maybe a couple of triangle braces.the top side would be rounded and taped.
    I've made a jig to hold the 2 at 90deg while i apply the fillet to the underside.

    I would also like to cut an oval hole in the vertical panel say 4x6" somewhere in the middle so i can access the inside,i also plan to keep the ends open.

    So my question,should the triangle braces that i plan for the underside go to the floor?Or would say 4"x4" ones be enough?I would like to keep the inside open and not chop it all up with braces.

    hope my question is clear,thanks
     
  2. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The wide angle photo makes it hard to gage the overall boat, but based on my guess-

    It would probably be better to pare away all the foam from about an inch either side of the joint and then bond the two pieces with a tape with everything flat. Then fold to shape, temp brace or install bulkheads, and build the fillet up with more tape forming a structural fillet of the desired radius with no waste. When you make the other side, use one top skin and two pieces of foam and save yourself the bonding. The joints to the hull and topsides would also be improved if the foam were gone and the joint was single skin.

    Any internal bracing needs to be calculated based on panel strength and panel loading and will depend on the properties of the foam and skins. No general answer can be given, but "ears" or gussets aren't normal. The three joints should be strong and stiff and support themselves over their length. It's the flats that might need help. If it were me, I'd make the seats identical to the hull or a bit thicker because they are flat. It's an open boat- there isn't much to be saved if you want it all to last the same.

    Please tell me the foam is at least 120 density and the skins are 20+oz weave on the exposed sides. If you build the entire boat out of 7mm ply, you would still need to add weight to it to make it row at its best. What is with the weight savings? Do you need to cartop it?
     
  3. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    Phil,yes the boat will be a car topped.The 1/4" foam is M80 and has 12oz biax on it so far.The bench will be wood and may or maynot sit on the floor when attached. and be removed when loading.

    From your responce i get that the joints need to be soild glass and the flats will need some help.How thick and how much do i stagger the joints?What about the vertical panel? This will take most/all the weight no?Is more glass the answer?i ordered the 1/4" a long while ago thinking i could use it but i no know thicker would be better,oh well use what i got.

    You mentioned the boat would row its best if i added weight,i don't quite understand.The boat rows really easy with 400lbs in it i'm just trying to lighten the load as it will be a hand bomb type boat.

    thanks..

    [​IMG]
     
  4. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Dont know much about foam core panels. If it was plywood, a double fillet " T " joint is very strong. Whether you can create a double fillet T at the bench structure to hull interface and the bench structure to hull bottom joint is a good question. Long arms !

    A knee or bulkhead at the oarlock position might be helpful and also address this inferior fillet

    Also think of physical abuse and misuse. Open ends on your structure are fragile.
     
  5. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    The second photo helps. I had misjudged the size of the craft. I thought it was about twice as big. M80 and 12oz is okay, but very easy to ding. I think I'd run some wood stringers inside to absorb abuse on the floor. 0.5 molded x 1.5 sided with a 4-6 oz skin would add a lot of protection to the floor. I'd build a little ply floor area just big enough to secure boat junk like the bucket you keep an anchor in. Use cloth pouches to hold everything else. Keep stuff off that floor.

    Ignore the added weight comment, I was imagining a different boat.

    I like Michael's suggestion about external braces tying the sides of the hull to the bench tops. They will add tremendous stiffness and generally be in the way so you won't stand on that area.:D
     

  6. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    OK so back working again I've filleted and taped the inside of the joint and cut out an oval hole for access.I'd like to add another layer of glass over the outside before i tab it to the sides and hull..My question is how to deal with the oval shape?Can i glass over then cut reliefs in the area and wrap the glass around the opening?I will use 12oz biax

    i've added a second layer of 1/4" foam to the back with some scraps to give it a little more thickness.I;ve also ran my round over bit on both sides of the opening.
    [​IMG]
     
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