Coring sources?

Discussion in 'Materials' started by silentneko, Feb 6, 2014.

  1. silentneko
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    silentneko Junior Member

    I might be rebuilding an older boat and since I do flats fishing I wanted to lighten things up, but within reason. The boat will be about 16ft or so and will be torn down to the bare hull.

    I was thinking about some honeycomb (nidacore, ect...) for the floor and decks and foam core for the bulkheads, stringers, and other structures. Can you guys give me a suggestion on thickness and products?

    I need direction on where to source my stuff and what to look at. Budget is key, I know I can build it all with okoume for $90-100 a sheet or so, or with meranti for $70-90 a sheet as I have done so in the past. Is it possible to find good composite coring for these prices? I live in central Florida if that helps. Can anyone direct me to an online supplier with reasonable prices and selection?
     
  2. rasorinc
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    rasorinc Senior Member

    Composits plus layers of fiberglass and resins will, most likely, create a heavier and more expensive boat than wood frame with ply over.
     
  3. Eric Sponberg
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    Eric Sponberg Senior Member

    SN, Fiberlay is a major composites supplier to the boatbuilding industry, and they have three locations in Florida: Miami, Sarasota, and Pinellas:

    http://www.fiberlay.com/

    Composites One is another major supplier, and they have locations in Lakeland, FL and Miami:

    http://www.compositesone.com/

    Nida core is a fine choice for interior decks. Decks on small boats are usually subject to just walking loads, so stiffness is key. Think about using 3/4" or 1" thick core with two layers of glass on each side, and that should be strong and stiff enough. For glass, I like to use combinations of 1708 double bias (±45°) stitched fabric with mat, plus 1808 bidirectional (0°/90°) stitched fabric with mat, topped with a layer of 6 ounce or 10 ounce plain weave glass cloth for a smooth finish good for minimal filling/fairing/painting.

    I hope that helps. Good luck on your project.

    Eric
     
  4. silentneko
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    silentneko Junior Member

    Thanks guys. I've been trying to work out the math for the weight difference. Anyone mind double checking my figured?

    For Plywood:
    ½” Okoume BS1088 is roughly 40lbs, and Meranti BS1088 is about 50lbs

    4’ x 8’ = 32 sq ft / 9 sq ft = 3.556 sq yds of surface area per sheet side.

    If I cover each side with a layer of 6oz cloth, as I have in the past, that will be 42.672oz per side assuming a 50/50 ratio of glass and resin.

    85.344oz / 16oz = 5.334lbs

    So the weight of a 4’ x 8’ sheet would be roughly 45.3lbs for Okoume, and 55.3lbs for Meranti.

    For 5lbs per cu ft composite:

    1” thick works out to 2.667 cu ft x 5lbs = 13.335 per sheet.

    If I cover each side with a layer of 1708 and 6oz cloth (this is what was suggested) that is 31oz x 3.556 sq yards = 110.236. Assuming a 50/50 mix of glass and resin then it is 220.472oz per side.

    So a 4’ x 8’ finished sheet would roughly weigh 40.9lbs

    Does this all sound close? So using composites would only save me about 5lbs per 32 sq ft of material used over okoume?

    If the math is right, then it really doesn't pay to go with composites for me.
     
  5. Eric Sponberg
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    Eric Sponberg Senior Member

    SN, your math is correct, but you are comparing 1/2" thick plywood with 1"+ thick of cored composite. The 1" cored composite is going to be a lot stiffer. If you compare the composite weight to plywood of equal thickness, 1", then your composite panel comes out ahead, about half the weight of the plywood option.

    As I mentioned earlier, for decks on a small boat, stiffness is key, and thickness is the driving dimension for stiffness.

    Also, I admit that my suggestion of using both 1708 and 1808 plus a 6 oz. glass is probably overkill. It looks like you used just the 1708 ±45° fabric n your calculations. Actually, in retrospect, I could suggest using just the 1808 0°/90° fabric with a peel ply on top for surface finish (pull it off after cure) and leave off the 6 oz glass. That weight would come out close to your numbers.

    You can try a simple test. On the ground, lay out some different thicknesses of plywood that are supported by 2x4s that are spaced apart the same distance as whatever supports the deck has in your boat. Stand in the middle of the panel and see how much it deflects. You'll likely see that 1/2" plywood isn't anywhere stiff enough. 3/4" plywood will be a little better. 1" plywood will be better yet. You'll find out quickly which thickness is adequate. You'll also see that if you move the 2x4s closer together, the plywood gets stiffer. This means that if you add more stiffeners by bringing them closer together, you can increase stiffness a lot.

    Generally, when you are figuring out structures, the panel size comprises about 2/3rds of the weight, and the stiffeners about 1/3. You can reduce overall weight by reducing thickness and adding more stiffeners.

    There is a lot to be said for simply plywood construction--it's easy and cheap, and it works well. Constructed well, it can be pretty light weight.

    I hope that helps.

    Eric
     
  6. silentneko
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    silentneko Junior Member

    Thanks Eric. I was comparing the 1/2" ply to the 1" composite because that was the general info I got when I called the suppliers. I've contacted 3 places (Bateau, fgci, and compositeOne), and they seem to agree that when using composites you generally double the thickness for structural strength.

    I've built 3 boats so far, all only out of plywood never used composites. I used 3/8" for the decks and floors covered with 6oz cloth on each side, the decks were supported every 16-18" or so and were solid as a rock. I'll most likely go this route again. I used 1/2" and 1", instead of 3/8" and 3/4", to make the math easier for the comparison. If I used just 1808, or just the 1708, and left out the 6oz cloth then I'd be saving another 5lbs or so per panel. Honestly I'd be nervous at this point because of dropping the anchor or cast net many times so I'd probably still do the 6oz. But even at 9-10lbs of difference between the ply and composite, I think the cost difference doesn't justify the weight savings.

    So I think I'll end up using plywood again. Thanks guys.
     
  7. silentneko
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    silentneko Junior Member

    Ok my math was off a little because one site told me 1708 was 17oz biaxial with 8oz mat, but every other reference I've seen says it's 17oz biaxial with .75oz mat. So I redid some figures, and this time I used 3/8" ply and 3/4" Divinycell. I also went ahead and calculated costs to see how effective it would be.

    3/8” Okoume BS1088 is roughly 30lbs and $90 per sheet

    3/8” Meranti BS1088 is roughly 37lbs and $70 per sheet

    ¾” H80 Divinycell is roughly 10lbs and $200 a sheet (I know there are other options but this is what’s locally available to me)

    My resin costs are about $0.37 per oz.

    If I buy fabric that is 50” wide then I’ll need 2.67yds to cover each side of the 4’x8’ panels.

    Again assuming a 50/50 mix of glass and resin then to cover a panel with:

    6oz cloth it will cost about $58.50 and add 5.3lbs

    1708 cloth (17.75oz) it will cost $113.46 and add 15.78lbs

    So my final costs and weights for the finished 4’x8’panels would be around:

    3/8 Okoume BS1088 with 6oz cloth - $148.50 and 35.3lbs

    3/8 Meranti BS1088 with 6oz cloth - $128.50 and 42.3lbs

    ¾” H80 Divinycell (5lbs density) with 1708 and 6oz cloth - $371.96 and 31.1lbs

    Looking at the actual numbers, at least to me, it doesn't make sense for my projects to more than double the costs, just to save 4.2lbs per 32sq ft of panels used. So over the course of the entire interior renovation I might be looking at only 30-35lbs or so difference spread over the entire boat?
     
  8. Eric Sponberg
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    Eric Sponberg Senior Member

    SN, I won't check your math because I assume that it is correct. Welcome to the wonderful world of boatbuilding. It is hard to beat plywood construction, at least on a one-off basis--it's simple, cheap, and weight effective. This is fine for decks.

    In production boatbuilding, process is as important as materials, and shape and finish are important as well, so composites are ideally suited for this, and you can make lightweight, pretty structures quickly and cheaply.

    In your example, building in cored composite over Okoume plywood is a price premium of $223.46 for a weight savings of 4.2 lbs, or $53.20 per pound. And you determine that that price is not worth it. That's a good judgment call. I recall in the 1992 America's Cup when A^3 was building their boat in Rhode Island, where I used to live, they determined that if they could save a pound of weight in the boat for less than $400, they would do it, but if the cost was more than $400/lb, it was not economically worthwhile for the overall cost of the campaign. I am sure in recent years that that rate has gone way up.

    Good luck with your rebuild.

    Eric
     
  9. silentneko
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    silentneko Junior Member

    Thanks Eric. It really doesn't make sense to me to go through all that expense just to shave maybe 30lbs off of a fishing boat. Plus I enjoy working with wood :cool:
     
  10. Tungsten
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    Tungsten Senior Member

    I'm assuming your using epoxy so you shouldn't be using glass with matt.Or I've miss read something.
     
  11. SamSam
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    SamSam Senior Member

    Fiberglass cloth is measured in ozs per square yard and fiberglass mat is measured in ozs per square foot. So .75 oz mat technically weighs 6.75 oz per square yard. Being kind of a random construction of sprinkled on chopped fibers, a stated value of 8 oz (or 3/4 oz) is an average, the actual weight can vary from different parts of a roll or from roll to roll.
     
  12. Eric Sponberg
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    Eric Sponberg Senior Member

    In regular plain mat that is held together with binder, the binder is soluable in styrene, which is the monomer in polyester and vinylester resins. The binder is NOT soluable in epoxy, but just makes a gooey mess. On stitched fabrics, the mat is stitched to the back of the fabric and it does not have any binder in it, so it is OK to use with epoxy.

    Eric
     
  13. Steve W
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    Steve W Senior Member

    No need for epoxy, a pp honeycomb core and pe resin will make you a more cost effective composite panel, I havnt run the numbers but I suspect it will be cheaper than an okoume/epoxy/glass panel.

    Steve.
     

  14. Steve W
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    Steve W Senior Member

    Ok, I just did a quick pricing pulling the numbers from express composites website as he has all the materials and I come up with $152.00 for a 4x8x3/4" pp honeycomb core with 1708 each side with pe resin, the weight would be comparable to your H80 panel so its looking very cost competitive with the okoume/epoxy/glass panel.

    Steve.
     
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