the right cloth and mat combination?

Discussion in 'Fiberglass and Composite Boat Building' started by JEFFHEENAN, Dec 16, 2014.

  1. JEFFHEENAN
    Joined: Oct 2014
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    JEFFHEENAN Junior Member

    Hello everyone, I am gearing completion of a drift boat plug and am wondering if there is any advice out there for me on layering my fiberglass cloth/mat to form my mold and ultimately boats. The boats will be around 16 ft X 5ft and I would like them to weight as close to 200 lbs as possible. I have 2.5 oz mat and 7.25 oz cloth. can I incorporate these or should I use heavier? Thanks for any input
     
    Last edited: Dec 18, 2014
  2. ondarvr
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    ondarvr Senior Member

    The cloth has no useful place in the drift boat, it's worthless for a project like this. And where did you buy 2.5 oz mat?
     
  3. upchurchmr
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    upchurchmr Senior Member

    ondarvr,

    I would like to hear an explanation of your statement.

    Jeff,

    Are you going to use resin? Epoxy or polyester or vinylester or what?
     
  4. JEFFHEENAN
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    JEFFHEENAN Junior Member

    I was planning on using a polyester gp resin.
     
  5. ondarvr
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    ondarvr Senior Member

    For a good, strong and long lasting hand laid laminate there should be CSM used between each layer of woven or stitched fabric. If you use a lightweight product like 7.25 oz cloth and CSM between each layer, by the time you build up the strength needed the laminate will have far too much CSM, resulting in a very heavy and relatively weak laminate. You will not meet your 200 lb goal.

    Cloth also has very poor bonding strength, so interlaminate shear may become an issue when the laminate is stressed.
    Cloth has very few benefits when used with polyester, so few that very few shops use it, or even have any in their plant. Also it is very high in cost for the little strength it adds. There are much better fabrics for use in a drift boat, even old school 24 oz roving is a far better product.

    I have never seen 2.5 oz mat, I’m not saying it’s never been made, because it could be manufactured, just that in 40+ years I’ve never seen any. ¾, 1, 1.5, 2, and 3 oz are the common weights.

    Your goal is to have less CSM and more woven or stitched fabric.
     
  6. ondarvr
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    ondarvr Senior Member

    Cloth is more frequently used in tooling because the fine weave has less of a tendency to print through to the surface, and the CSM creates a more rigid laminate (don't confuse stiffness with strength), the extra bulk and lower strength aren't as critical in tooling.
     
  7. JEFFHEENAN
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    JEFFHEENAN Junior Member

    You refer to roving, cloth, and stitched fiberglass. What are the differences and or benefits of each? Boat "D" Midweight • 7532

    I have a roll of this, is it good for anything?

    Has a more open weave and conforms to MIL-Y-1140. •Width: 38"
    •Wt: sq yd 7.25 oz
    •Thickness: 10 mil
    •Count: 16 x 14 (warp x fill)
    •Standard volan finish is compatible with polyester, epoxy, and vinyl-ester resins.
    Material will be shipped
     
  8. ondarvr
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    ondarvr Senior Member

    That product really won't work well in the drift boat, it will work OK for making the mold though.

    A typical drift boat has rather thin hull sides, very thick chines, and a thinner hull that will flex. There is a segment of the market that makes rigid cored hull bottoms, I don't recommend the cored hull bottom because it creates many problems in the future.

    You will need to decide how you plan to use the boat before deciding on fabrics and laminate schedules, especially if you want it to weigh around 200 lbs.

    Most drift boats are made with 1.5 oz CSM and 24 oz roving, fewer are made with 1708, I would go with 2408 or 3208 if you can find it (less CSM and more Biax)

    One reason for 24 oz roving is that it gives a fairly decent surface on the inside of the boat without much work, 1708 can have a less appealing surface. One option on 1708 is to use a 1.5 oz CSM first, then turn the 1708 CSM side up, this way there is a CSM finish. Or you can use1708 and roving as the last layer for cosmetics.

    I made several with Biax and last layer of roving, I also made some using VE that were in the 200 lb range. My current DB has 60 oz Traix in the hull bottom along with a roving finish, this boat was modified a great deal and designed for more abuse, so it's a bit heavier.
     
  9. SamSam
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    SamSam Senior Member

    Cloth weights are per square yard while chopped strand mat weight is per square foot. It's a mystery to me why it's done like that.

    So a square yard of your 2.5 oz csm would weigh 22.5 ounces, combined with the cloth it would weigh 29.75 ounces per square yard. Then the resin weight is added to that. Depending on the method of laminating, open mold by hand, vacuum bagging or infusion, and your skills, the final laminate will have a glass/resin weight ratio of 30/70 to 50/50.

    There is a chart here showing various combinations of materials and their weight and thickness. You need to click on it 1 or 2 times to make it laege enough to read.

    http://www.boatdesign.net/forums/fiberglass-composite-boat-building/fiberglass-thickness-8686.html

    .
     
  10. gdavis
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    gdavis Junior Member

    hello jeff.....Always start with a mat and always finish with a mat. Are you using gel coat on the exterior ? If so, 1st,gel coat, no wax, 2nd, 3/4 oz mat, 3rd, 1 layer 1708 0-90 sides and bottom,4th, 1708 +-45 sides and bottom,5th, 1708 0-90 in the bottom, last, 3/4 oz mat sides and bottom with a bit of wax. Vinylester resin is the way to go,polyester is taking a back seat these days. The last layer of 17080-90 in the bottom should come up onto the sides about 4" this will make the chines stronger and a few tapes up the inside of the bow wouldn't hurt either. I have seen bulkheads running from the bottom of the middle thwart down to the bottom stopping short of the sides, this really stiffens up the bottom. You don't want the bottom to flex because this will cause it to crack and eventually fail.(you get wet). Also having water tight lockers bow and stern will help stiffen the bottom. If you hit rocks this boat needs to ride up and slide off, no flexing! Strait forward and simple glass work. No need to infuse, just don't over do the amount of resin and carefully bubble pop between each layer, get all the trapped air out. If you plan to paint the inside leave the wax out of the last layer of mat, this will leave the resin sticky for a while, put the paint on while its still sticky and it will burn right into the resin, It will not come off, never! If you plan on really bashing around while chasing those fishes you can add 1 more layer of 1708+-45 in the bottom before the finish mat. You won't notice a little extra weight when drifting down the river at dawn watching the ripples of a rise and making that perfect cast immersed in the moment. Whoa. Hope this makes sense to ya. Save that cloth to use on a stripper canoe built for the still waters.......peace,out..................g.......
     
  11. ondarvr
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    ondarvr Senior Member

    Let me jump in again, I've made drift boats, have drift boat molds, and I supply all the major builders of drift boats with materials, I'm very familiar the correct ways to build them.

    For rowing purposes a rigid bottom works well, for sliding over rocks and taking a beating, bottom flex is a good thing.

    You do not want anything attached to the hull bottom that spans any distance, it will create a hard spot and may cause cracking, frequently to the point of failure. Dry boxes, seats, level flooring (an option), fish boxes, etc. are all suspended up off the hull.

    The chines are reinforced with multiple layers of whatever fabric you are using, up to 12 more layers of it in some boats. This is just full length 6" strips that are staggered slightly side to side.

    The addition of a final layer of CSM is wasted money and additional weight, that's why everyone goes with a roving finish (well a couple do use chop), it reduces weight and does add some strength.

    Depending on the type of gunnel used on your design there things done to improve strength. If your design has straight sides and a wooden rail at the top make sure it's thick enough so that lifting and handling the boat doesn't create a cracking problem.

    For a rolled gunnel design add another two layers or more of fabric in the gunnel. Making the gunnel thicker allows you to make the side wall thinner and still keep a solid and strong boat. It also makes it much easier on your hands when lifting and moving the boat. Some companies use a plastic molded edge (bang on), but it frequently comes off, it is easier on the hands too.

    Side trays, seats and other things will also strengthen the sides.

    If you want light weight you really need to pay attention to the amount of resin used, keep the laminates as dry as possible, no runs or puddling should be seen. Use as little CSM as possible, it just adds weight. If you start adding a bunch of stuff like the options you see on many boats the weight will add up fast, a couple hundred pounds can be added quickly.

    Gel coat is used as the interior finish, paint doesn't hold up well in this application.
     
  12. Commuter Boats
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    Commuter Boats Commuter Boats

    You seem to be situated right in between Fiberlay and Composite One, are you with one of them?
    Gerald
     
  13. ondarvr
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    ondarvr Senior Member

    Not one of them, I do supply Composites One with resin and gel coat though, they distribute products I sell.
     

  14. Commuter Boats
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    Commuter Boats Commuter Boats

    Thanks, PM sent...
     
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