layup schedule over corecell and coosa?

Discussion in 'Boatbuilding' started by leaky, Apr 8, 2017.

  1. leaky
    Joined: Sep 2008
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    leaky Senior Member

    Hi,

    I've got some parts to build, depending on the part it's one of 2 cores, 5 lb corecell and 26 lb coosa, with the coosa really being the hardcore structural/wear areas and the corecell being more superficial/semi-structural.

    V berth - this is going to be a big triangle piece with no cutout in the middle that is about 7 ft long X 6 feet wide, kinda a narrow triangle, which is supported on the wide end by a bulkhead (there is bulkhead closing that part of the boat off and a door cut in the center so you can climb in, all 3 sides of the triangle are supported). Planning on this being built from 1.25 inch of corecell and would like it to span without support underneath ideally. The top of this I'd like to be able to resist damage from people climbing around and large fishing reel storage, like a 130 class reel bouncing around.

    Interior bulkheads and other parts - bulkhead mentioned above, bulkheads for enclosed head, kitchenette parts - all will be 5/8 corecell.

    Exterior bulkhead - the backside of the pilot house, the "winterback", will have a wall going in that closes the pilothouse off from the cockpit with a door; it will be 5/8 corecell.

    Stringer extrusion, the stringers existing today are 1 inch coosa and I will be making them taller by tabbing them into the existing and encapsulating.

    Deck, 3/4 coosa. This will be built out of 3 pieces that go the long way. Each of the 3 pieces will be built out of 2 pieces cut from a 4X8 sheet (for instance about a 2X8 and a 2X8 will be joined end to end to make a 2 X 16), the top and bottom will need to be glassed over or tabbed together such to make them a single part - ideally such that it does not cause a cosmetic issue on top. The 3 main pieces will be set down on a structure underneath that spans the whole seam; they will be glued to it (essentially tabbing the underside together), then the topside will be tabbed to the hull and glassed over.

    Thanks in advance!

    Jon
     
  2. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    You only need high density coosa if you are going to put screws into it. Otherwise go with the corecell. My entire deck on a flats skiff 22 foot by 8 foot is the 5 lb density corecell with 36 oz biaxial infused. My stringers are also corecell but that depends on your boat and design, my transom is 26lb coosa 1.5 in thick. I have the corecell, I think 1/2 in spanning 31" the deck and I don't notice any softness.
     
  3. leaky
    Joined: Sep 2008
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    leaky Senior Member

    What I'm really wondering is what sort of glass to be using, like on an interior part is a layer of matt, 8 ounce cloth, and another matt about good enough, or should I go at it w/ a biaxial 1208 or 1708.. Then similarly on the deck, is one layer of 1208 followed by some matt enough on top or way too much or about right?

    The stringers, to me seems like if they are tabbed into the existing w/ a couple layers of 1708 that's pretty good, maybe I won't try to make the bend over the top w/ 1708 but I'll do that w/ some matt and separate layers of cloth instead. But maybe that's wrong.

    I get that you can make a deck out of corcell or nidacore and I put some strong consideration into it. My issue is this is a 32 ft downeast which will be used as a workboat to some extent. We drop anchors, 30 lb bags of ice from the pier 15 feet overhead, gear, fish (like loading 800 lb fish), and that sort of stuff down on the deck regularly.

    I believe any weight savings I try to get out of the corcell (or similar) is going to be just about eaten away by #1 needing to put more structural glass on the bottom side of the corcell since coosa doesn't really need any #2 needing to put more structural glass atop of the corcell to protect the relatively fragile core against puncture wounds. When I do the math that biaxial you put on there (assuming one layer top and bottom and no other glass) would get a 3/4 4X8 piece of corecell up to around 40 lbs, a similar piece of coosa is about 52 lbs and the glass aspect is more negligible since so much isn't required. If I did it all just that way I could see maybe shaving 100 lbs in this boat, but if I needed additional glass or matt on top or the corecell takes up significant resin, then it might end up being the same weight for a weaker deck.

    Jon
     
  4. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    That's pretty extreme, in that case I believe you would want some kind of support under the deck at that point and also some kind of rubber mat on top and the weight be what it is. On the stringers I used UNI cloth since that gives the strength in the direction you need it but you can also throw a couple layers of 0-90 or 45 on there. I do believe you want to go over the top. Generally the stitched fabrics are stronger than mat or woven but I don't know about all the impacts etc, maybe somebody else has experience with that.
     
  5. leaky
    Joined: Sep 2008
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    leaky Senior Member

    Thanks for that. The guy at the shop I've been working with to supply materials strikes me as a minimalist who tends to see a lot of lightly used boats, said I'd be crazy to go over coosa with a layer of 1708 and actually recommends the light foams like corecell on the deck too. He was saying with coosa a layer of matt, some cloth if it makes me feel good, and a layer of matt on the deck is all I'd want or need atop coosa but that sounds too chincy to me so looking for another opinion.

    There are 4 stringers, which will be crowned with angle pieces of fiberglass to create a seat for the long edges of the 3 coosa pieces that will makeup the deck, they will be glued to it when set into place. It's not that wide of a boat, deck is 10 ft across at it's widest point. The worst span is 30 inches. Basically you got 30 inches between the stringers then a little more than a foot between the outside stringer and the side of the hull where there will be a seat for the outside of the deck. With plywood they use 3/4 but sometimes 5/8 to take some weight out and do not usually frame width-wise, the 4 stringers alleviate the need. I figure 3/4 coosa should kill it - actually could go down to 5/8 coosa but similarly to some other ideas, shaving 48 lbs while minimizing deck strength just doesn't seem worth it for this part. I will be cheap about the weight elsewhere.

    The nice thing is even with the coosa, I'm shaving 150 lbs off the way about every other one of these boats is built in the deck alone, and probably a ton more as the plywood starts to become moisture ridden as they do when you do not glass the bottom side, so I will be within a good weight budget no matter what I do.

    I had a post going on core choices awhile ago and have gotten recommendations across the board on everything from the light foams and honeycomb to balsa and plywood. There is no doubt in my mind without consideration of the bad properties of balsa it'd be the lightest thing for having good strength/resistance, and that plywood is the most practical, but for what it is I keep ending up back at the coosa due to it's similarities to plywood and non-rotting nature. This boat has no wood in it anywhere else and I don't want to add any other than maybe some cabinets.

    Maybe though upon further consideration I find loading the hell out of the topside of a light foam with fiberglass, even if there is no weight savings over coosa but it's similar, ends up being the strongest thing. I would not be unhappy to find it would make sense to do something like that as I can get practically anything else cheaper than coosa.

    Jon
     

  6. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    Coosa is extremely tough stuff, I agree go with the coosa. As for the laminate, it's the first skin that gives you all the bending strength but if your going to be dropping stuff on it from that high up, then you need to consider adding whatever other work boats do. In my opinion a simple rubber mat would go along way to helping prevent chips and cushioning the impact. Good luck on it
     
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