Kurt Hughes Daycharter 36

Discussion in 'Boatbuilding' started by Charly, Mar 10, 2010.

  1. Charly
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    Charly Senior Member

    Hello! Thanks to you all for such an interesting and educational forum. This is my first post here. I hope I can learn and add something useful to the mix at the same time.

    My project is finally starting to materialize, after some planning and saving, and a lot of laying awake at night. I have purchased the plans and enough plywood for the hull skins, and now, within the next month or so, I hope to actually start building.

    The first phase of the project will be to build the molds, and lay-up the hull sections. For anyone not familiar with this type of build it is explained in detail on Kurt Hughes' website, and is called "cylinder mold" construction. Briefly, it involves laminating full sheets of 3mm plywood together (in my case, a 36' cat, the hull sections are three plies thick), with epoxy resin, on a male form that is basically half of a hull. The two half sections are then stiched together at the keel and the stem, the bulkheads are then added, then the deck.

    I would especially like to hear from anyone that has actually built using this method, as I am sure I will have a lot of questions. As soon as I have something to show I will post some pics.

    OK my first question:
    Right now I am thinking about stringers, especially the sheer. The plans call for laminated spruce, but as y'all know, spar grade spruce is quite expensive. My local lumber yard sells spruce framing lumber that is fairly reasonable (pricewise). If you pick through the stacks there are some tight grained, and pretty straight boards in there. What say ye? Oh, and this- what about three laminations as opposed to two, as the plans call for (maybe the extra epoxy weight could be offset by making the sheers triangular-taking away some deadwood) Should each individual strip be a minimum length for a 36 foot boat? What is the shortest length stick you would use on a laminated stringer?

    Enough for now. Thanks for all inputs.
     
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  2. Charly
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    Charly Senior Member

    Well, I have finally actually produced something. The first cylinder mould session went pretty smooth. The worst calamity was when I ruined a 30 foot tape measure in a weak moment of doubt when I went to measure a wet peice of okume, and got resin all over the tape.:eek:

    some notes:

    I used 6 mil poly for the bag. For sealing, I took sections of3/4 inch pvc conduit, glued up into two long 38 foot pieces, and duct -taped them to the long edges of the poly, (with the tape on both sides of the plastic). Then on the bottom one, I unrolled and laid out a continuous piece of rope caulk, about a half inch away from the conduit. When it came time to seal the bag, all we had to do was to press the top piece snugly against the bottom piece, and down into the rope caulk, and then roll the whole thing up for several turns and clamp them every few feet. The hardest part is keeping it rolled up tightly and neatly until you can clamp it in place. But it worked great, and was fast.

    I found it easier to just cover all exposed plywood edges on the male forms with duct tape than to sand the splinters off.

    the cleat on the bottom of the form. when slacking off the screws to open it up a little bit so that the three layers of okume will all fit, I was worried that the okume might actually sip down inside too far, and bind everything up- preventing a tight clamp with the screws. So I screwed on a ledger at the same height as the form, to the inside of the board... which would move with it when the screws were slacked off- that way, the plywood could not get down between the boards of the form, and the longitudinal board that screws into them.

    The numbering and lettering of each piece made everything fall into place without having to think anymore about layout. This was a big big help. On the KH36, the plys are scarfed and joined to make them into 8x8 (actually on mine 8x7) panels. Since the length and freeboard of each boat is different, they all have their individual layout quirks, but having one scarf line fall atop another scarf line on a different layer (three layers in a KH36) is a structural no no. In addition, the bevels all have to mate up, so it takes some planning and thought. When space is limited, it makes it all that more difficult to keep track, because you can't just spread a bunch of 8x8 panels around like a deck of cards. I used an alphabet system A, B, and C for each sucessive layer, and a fore and aft numbering system for each individual layer. Since the panels on my boat are seven feet high, this makes for a four foot wide sheet of ply, and a three foot rip. So layer A gets a four on top and a three on the bottom, followed by a three on top and a four on the bottom, etc. This layer staggers the horizontal breaks. Then the vertical breaks are staggered, in my case three layers, so cut the first panel on the A layer 32inches long, the first on the B layer 64, and the first on the C layer gets a full 96. Kurt says in the instructions that this should make the fold-up go easier at the bow section also. I numbered mine with a magic marker in the top left hand corner of each piece of the puzzle, and also wrote on red ink on the sides that get no epoxy. I was paranoid that my helpers might coat the wrong side in their enthusaism.:D

    Now I have a question for those more experienced:
    I have one spot about a foot square that rings hollow-- right at the turn of the bilge, near the transom. I have never fixed this kind of thing before, so should I drill a bunch of holes and inject some thick resin? could I use foam-- and If I do how much "relief" holes should I drill to keep it from pushing out? Is there anothr better way to fix it? It will eventually be sheathed in cloth.

    One down, three to go.

    All inputs welcomed.

    Charly
     
    Last edited: May 30, 2010
  3. Charly
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    Charly Senior Member

    OK, the second session went fine, but I still have this void spot at the turn of the bilge on the second panel, in the same place. Any ideas how to treat it?

    The 1088 okume is a bit too stiff, I guess. But now, port must match starbord exactly, so I am afraid to do anything different to compensate, out I fear that I may end up with two different sized halves. I am wondering if I should treat the voids before foldup, or after
     
  4. hoytedow
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    hoytedow Wood Butcher

    Hi, Charly. I would stand the void vertical with only a hole at the bottom. With a caulking gun I would force suitable compound in from top until it oozed out the bottom. Others may suggest the best material for this. I would not use anything too runny because yoiu want to force as much air out through the bottom of the void as possible.
     
  5. Charly
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    Charly Senior Member

    Thanks hoyt,
    Do you think I should do it now or after the foldup? It is between the outer layer and the middle layer of 3mm okume.
     
  6. hoytedow
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    hoytedow Wood Butcher

    I would do it before the build progresses any further. If you have a way of injecting epoxy that would probably be best but 3m 5200 in a caulking gun would be great too. Once it oozes out the bottom plug the hole so it won't all run out from the top down. Give it time to set properly. I invite any contradictory anecdotes here as I don't have a tremendous amount of experience in this regard.
     
  7. apex1

    apex1 Guest

    Now.

    and thicken it to honey consistency using a light filler like microballoons or better cotton strand fibre (I assume ep, right?).


    edited:
    I am not really familiar with the method but as far as I grasp it, you bend the panels further when joining? In that case the void could collapse, therefore I said Now.
    If there is no further stress applied, then it would make more sense to do it later with more fibre in the resin to make things easier and to have the resin cured "in shape", where it provides the optimum strength.

    Regards
    Richard
     
  8. Charly
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    Charly Senior Member

    right.

    Do we have a "5200 school" vs "epoxy filler school" argument shaping up here?:)
     
  9. hoytedow
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    hoytedow Wood Butcher

    Nope. I just know the 5200 comes already packed in a caulking tube. It might even be acceptable to use silicone caulk but until someone with more experience recommends it I won't either.:)
     
  10. apex1

    apex1 Guest

    Not that I would know. But being a European I´m not familiar with 3M stuff. And why would you use a different glue?

    Btw. my former post was edited!!!!

    Regards
    Richard
     
  11. hoytedow
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    hoytedow Wood Butcher

  12. mark775

    mark775 Guest

    I wud use EP, as well, but wud leave it thin and inject with surringe from bottom until it came out a hole at the top - maybe even plug the hole at the top with a gloved finger tip to force epoxy into the taper of the void. be prepared with the correct size plug at the bottom - don't rely on tape (our first instinct!) unless you are very confident, as you will undoubtedly spill a little Ep, the tape will only stick to this long enuf for you to turn your back, then...
    I also don't think of 5200 as a very good void filler - I suppose one could warm it to thin but Ep is ready made. If you fill before it is bent to final shape, it may create a hard (stiff) spot if the void is thick. I wud trial bend it and get a feel for fairness as is - fairness is the goal, correct? If it is not fair in trial, then fill with slow hardened Ep and bend while it is still green. Without knowing how much bending of what plywood (BS1088 doesn't tell enuf) will take place, how many plys are already together, nor how thick the void is, I think filling pre-bend is scary if there is very much more torturing to take place. What BS1088 are you using? A lot of stuff cud say "meets BS1088 standards" and whatever agency in England not even know it exists. I vote for Shelman okume as it bends some and has an anti-fungicidal glue.
     
  13. hoytedow
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    hoytedow Wood Butcher

    So, there you have it, Charly, a great detailed answer. Two votes for epoxy, with a good explanation why filling from below is better. Build the inlet hole and plug ahead of time. After is too late. He is right about the tape, too. If I had a dollar for all the glue I've let run out of a plywood void, it would be stuck to the floor.
     
  14. Charly
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    Charly Senior Member

    Hey Mark,
    They are pretty good sized voids-- about16 inches diameter. From what I read in the manual, there is quite a bit of "fight" involved, in the foldup-- especially at the bow. What apex said about collapsing was my first thought, but then this is going to be a good sized hard spot, so it also seems to make some sense to have a more flexible filler- even so, with no place to go, it might not make any difference. I guess I would rather have to do some extra fairing though, than have a blowout to repair...

    Okume BS 1088, via Boulter plywood from europe. That's all I know.
     

  15. apex1

    apex1 Guest

    That is not a void, thats a valley.

    Never you can fill that prior to bending the ply further! But you could "drip" some neat epoxy in to avoid a collapse, then fill after bending with fibre thickened Ep.

    Regards
    Richard
     
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