2-4oz glass over Xynole?

Discussion in 'Materials' started by abosely, Jul 31, 2015.

  1. abosely
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    abosely Senior Member

    When sheathing hull (Wharram Narai) with Xynole, would there be any benefit to add layer of 2-4oz glass cloth over the Xynole?

    My thoughts were that since Xynole uses about the same amount of resin as 10oz glass cloth and tends to have rougher finish after wet out.
    That using 2-4oz glass cloth and laying it up at same time as the Xynole, the light weight fiberglass cloth would be used as a vail and wouldn't need much if any more resin to wet it out if the layup was covered with peel ply squeegeed down to press excess resin into fiberglass cloth.

    It would give a smoother initial finish and add a little more abrasion and possibly puncture resistance.

    It wouldn't add much weight if it basically used mostly of the resin in the Xynole that is hard to get squeegeed out. Maybe?

    Or maybe its a totally unwise idea. But thought I'd ask, just in case.

    Cheers, Allen
     
  2. rasorinc
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    rasorinc Senior Member

    I'm no expert but Xynole will stretch a lot before tearing and that is why it is used for abrasion resistance and it is the best for that. Putting 2 to 4oz cloth over it I would think if you beach your boat that you will be having a lot of that 2 to 4oz covering cloth hanging off the bottom.
    Just my 2 bits.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Putting 'glass cloth over Xynole is self defeating. Xynole is 6 times more abrasion resistant than 'glass cloth of the same weight. Xynole will not add any strength, nor any additional stiffness, just far better abrasion protection.
     
  4. abosely
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    abosely Senior Member

    Ok, then that's not something I will do now.

    What got me thinking about it, was thinking if had Kevlar on exterior of hull, then having light glass cloth over it to help prevent sanding into Kevlar & having it fuzz up & if it got scrapped lightly the glass cloth would take it before getting to Kevlar and having fuzzed up Kevlar to deal with when repairing scuffed area.

    Approximately how much does Xynole weigh when filled with epoxy per sq ft?
    I know it can vary a good bit, but remember seeing it mentioned but can't find it now.

    If peel ply is used over Xynole and squeezed well to remove excess resin, will that help reduce the weight of the epoxy, or is the epoxy needed (referring to what can be squeezed out by using peel ply) in the Xynole?

    Cheers, Allen
     
  5. PAR
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    PAR Yacht Designer/Builder

    Xynole is a modi-acrylic and absorbs a lot of resin. This resin rich sheathing is one reason it's so abrasion resistant. Depending on application, you'll use a minimum of twice the resin to fully wet it out and over three times the resin, on a less than ideal hand layup, so it can add some weight.
     
  6. abosely
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    abosely Senior Member

    Yes I heard Xynole uses a lot of resin for the weight of the cloth.
    I think it was that 4oz Xynole layup would weigh about what a 10oz glass layup would weigh as a rough guide.

    When starting with a hull in 9mm Hydrotek to be sheathed with Xynole.

    Was thinking to put one squeegeed, mashed in coat on the plywood, making sure no puddles or wet spots are left and there are no dry spots and let that set probably till next morning.

    Then drape Xynole and start wetting it out in middle and work towards both ends. Will have me and two other people (that know how to work a squeegee) helping spread and one person operating the Sticky Stuff Dispenser and supplying epoxy) wet it out then lay peel ply on it and squeegee it down smooth & tight. Then next day repeat on other side of hull, so over laps at bow & stern posts can be folded over and have green epoxy for bonding. It's a deep Vee hull that will be upside down.

    Suggestions & input?

    Cheers, Allen
     
  7. PAR
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    PAR Yacht Designer/Builder

    I think you have a good idea, but xynole tends to swell up when the goo saturates it. It also tends to float on the resin, both of these traits make it more difficult to apply, compared to regular cloth. Simply put, you can starve the fabric if you get too aggressive with the smoothing operations. To help hold it on the surface I like to apply it over slightly tacky goo, not dry. Is it possible you can bag your cat? Bleeder cloth and peelply will go a long way to controlling the smoothness and resin content.
     
  8. abosely
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    abosely Senior Member

    I guess I could. I haven't thought about doing so, but it's a straight curve, no compound curves at all, because it's 9mm ply over 1x3 stringers.

    It would be worth going to the extra effort because is about 5' x40' (32' at keel)
    so there's a of of surface area that if i have only a little bit of extra resin on most of it, that would add up since I have 4 sides not just two since she's a cat.

    How elaborate of a vacuum system would I need to pull a vacuum on an area that large? Will I need much in the way of gages & special hose fittings? I've only seen where elaborate systems were being sold for production type situations, on Fiberglast.com etc...

    Vacuum bagging it would give the correct amount of resin, well compressed cloth fibers and a pretty smooth finish too, I would think. I know it will need sanding and fairing, but would be a nice starting point

    I want to build her to a high professional level of workmanship, not a rough homebuilt job, just to get her on the water. Not only in looks but in quality of materials and construction and something that I want to have for a very long time. I want to do things right.

    Cheers, Allen
     
  9. tom28571
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    tom28571 Senior Member

    Here is some data on weights of different sheathing materials with epoxy.

    Sheathing weights:

    One coat of epoxy = 0.036 lb/sq ft
    Two coats of epoxy = 0.059 lb/sq ft
    Three coats of epoxy = 0.081 lb/sq ft

    6 oz FG cloth w/3 coats epoxy = 0.142 lb/sq ft

    10 oz FG cloth w/3 coats epoxy = 0.195 lb/sq ft

    XYNOLE cloth w/3 coats epoxy = 0.36 lb/sq ft

    KNITEX biaxial (non woven) FG cloth w/3 coats epoxy = 0.46 lb/sq ft

    These sheathing weights are approximate and will depend on how the individual applies the materials but may be helpful for those interested in these details.

    As others said, there is no point in covering Xynole with fiberglass in most instances.
     
  10. abosely
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    abosely Senior Member

    Thanks Tom for the data. Yea, I realize that was a dumb idea now.

    Since puncture resistance more important in my situation (lots of lava rocks) I'm putting 5oz Kevlar on inside of hull. The hull is 9mm ply and I'm putting Kevlar 38" up on each sheet before putting gluing to stringers, also covering Kevlar with 1.2oz polyester veil to make it easier to sand smooth and not fuzz up Kevlar. Before butt blocks go on will put Kevlar tape over seam.

    Thinking about putting second layer of Xynole below waterline.
    I'll be using peel-ply to minimize excess resin and keep the little nubs from standing up and have smoother surface.

    I know it adds weight and I'm trying to be careful and not unnecessary weight, but but on Big Island HI here getting pushed into or against rocks is all too likely, even tho being careful of course.
    The lava rock is so abrasive it can scratch & gouge pretty quick.

    Not so much worried about looks, but rather getting a small scrape or gouge and not realizing it and water getting into plywood and causing problems.

    Cheers, Allen
     
  11. rasorinc
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    rasorinc Senior Member

    I would go with thicker ply after what you said about rocks. Then make a plan to protect the thicker ply. 5/8 or 3/4 this is your primary rock strength.
    Do it in 2 layers 2- 3/8 or 1 -1/4 and 1-3/8. This will also give you a finished side up and down.
     
  12. tom28571
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    tom28571 Senior Member

    Good idea. Using Kevlar on the inside is the best defense against penetration with malicious floating stuff and dragons.
     
  13. abosely
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    abosely Senior Member

    razorinc, you got me thinking about thicker hull plywood. Keeping weight down is important on the Narai. So using thicker ply or laminating plys to get thicker hull would add to much weight.
    But, a modified version of laminating an additional layer of ply only where it will help with below waterline puncture resistance so adding more weight necessary.

    I read tests using Kevlar in the layup to get maximum benefit from the Kevlar. I can't remember where it was tho. But as has been mentioned Kevlar works better on the inside of the hull for puncture resistance.

    It was found that the best puncture resistance was with the Kevlar sandwiched between two skins. As in plywood, Kevlar, plywood. Which makes sense, the Kevlar holds the ply skins together to reduce shattering.

    So, my idea is laminate ¼" ply to the ⅜" hull ply between the lower 3 stringers and put small fillet on 1/4" ply to stringer to tie them together better. So it will be ⅜" hull ply, Kevlar, ¼" ply below waterline, except for stringers, which would be ⅜" ply, Kevlar, 1x3 stringer.
    The distance between stringers varies from about 6" to 8" along hull. So will add minimum weight but maximize the benefit of the Kevlar. I won't put a veil over the Kevlar since won't be sanding it for nice finish. So that will save a little weight, not a lot, but every bit counts.

    I don't think it would gain much by using 3/8" ply on inside since the inside laminate is more to stabilize the Kevlar, from what I understand.

    Cheers, Allen
     
  14. Tungsten
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    Tungsten Senior Member

    Just a question,theres been no mention of any structural type glass?Just from reading and seeing pics around here you normally see a layer or two of some.Then the Xynole over top.
     

  15. abosely
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    abosely Senior Member

    The Narai Mk IV is an older design of Wharram's and was before epoxy & glass, so didn't have hull, keel area glassed. Originally they usually used Cascover & Resorcinol to sheath hulls.

    A couple building one in WA state has a blog, buildingtiger.blogspot.com and they put on 5 layers on hull, keel junction.

    I'll check with Wharram about it and probably do the same to tie it all together, then Xynole over it.

    Will be using a semi sacrificial rounded keel shoe of Ipe over keel after keel has all the glass layers done. It will be glued and screwed with bronze screws (screw holes plugged with Ipe plugs) to keel. The spot where screws go into keel will be drilled out larger than screws and filled with thickened epoxy, so if water ever gets around screw, it doesn't contact the keels wood.
    There are 5 layers of 1" thick pieces laminated together for keel. The last 2 layers will have screw holes drilled over size and filled with thickened epoxy also and layer of glass between last 2 laminations to provide a barrier to rot if gets started somewhere in keel. Then 5 layers of glass over keel, hull junction. Then the Ipe keel shoe.
    The Ipe will be coated with epoxy and have a UHMW tape on it.
    The Ipe is incredibly hard, durable & rot resistant. The boardwalk at Coney Island was made from it and lasted 20 years. I've worked with it some, it's an interesting wood, too heavy to use much of it tho.
    Eventually when it needs replaced, it will be sawn off, ground down to remove it. But it should last a very long time. It does take some care gluing, but does well with right system.

    Cheers, Allen
     
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