Fitting Fiberglass Fabric

Discussion in 'Fiberglass and Composite Boat Building' started by tomherrick, Feb 21, 2012.

  1. tomherrick
    Joined: Sep 2006
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    Location: Versailles, Kentucky

    tomherrick Junior Member

    I'm new to fiberglass and most particularly to the details of fitting fiberglass fabric to a form. The books I own provide lots of technical advice on laminating, but none on fitting the fabric around curves and other shapes. I've found nothing on YouTube or elsewhere on the Web that shows how it's done, except for very thin cloth over wood structures, e.g., kayaks where it's just draped. I don't have any problem with scarph joints and staggering joints between laminations; those aren't the issue.

    My project involves 1708 biaxial and epoxy over a C-Flex male mold; project description elsewhere on this forum. Due to the fairly heavy fabric (yes, I'm married to it now) I'll be using vacuum to hold the wet layup material in place (peel ply - perforated release film); no infusion.

    What's confounding me is how to cut the material to fit around curves in the transom cutout and gunwale, and at the end of the running strakes. I've never done any sewing but for patches on my jeans in the 60s, so cutting fabric to fit a particular form is foreign to my experience. Can anyone steer me towards a good book or three on how to do this work?

    Photos showing the areas of my consternation are below:

    Transom Cutout Curve
    [​IMG]

    Gunwale Transition and Curves
    [​IMG]

    Running Strake and Transom Corner
    [​IMG]
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    1708 is not that heavy and rather easy to form once it is wetted out. You don't need to vaccuum bag it. A set of two or three different size laminating rollers to push it in should be enough.
     
  3. tomherrick
    Joined: Sep 2006
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    Location: Versailles, Kentucky

    tomherrick Junior Member

    For some reason, the 1708 keeps pulling away from the outside edges of the running strakes, leaving bubbles and un-laminated fabric. Last time I stayed with the laminate for nearly two hours with rollers and squeegees and it still pulled up. I'm too old for that... Otherwise, it does lay down pretty well.
     
  4. CatBuilder

    CatBuilder Previous Member

    It's pretty simple, actually... though I was as stuck as you are when doing the trailing edge of my rudders and dagger boards. You have two choices:

    1) Make the corners less sharp and more rounded - give them a slower transition

    2) Use lighter cloth on the tight corners

    For instance on my really tight areas (trailing edge of a rudder), I used 34oz triaxial - a real man's cloth - ha ha ha ;) Ok, so I used 34oz triaxial, but stopped it short of the sharp corners.

    I had a 2" wide rebate sanded into my foam along the area where I wanted to lap the 6oz cloth. I would imagine you can do this with wood as well. The rebate allowed the 34oz fabric to dip into the core just a touch, so it didn't create a spot that wasn't fair once the layers of 6oz cloth went over it.

    Over the rebate that allowed the 34oz fabric to dip into the core, I then laid an equal or greater amount of 6oz cloth to make up a similar strength and bent that 6oz cloth around the difficult corner or edge.

    These were foils though. You may not need such perfection. In case you don't want to do rebates, you can just pile the 6oz cloth over the end of your 1708 and have a lap joint there that sticks up. You can then fair that down later during final fairing by building up around it to ease the hard bump out.

    For really *really* sharp edges, dull the edge down a lot until it's dull enough to glass over, then build it up using thickened epoxy over the glass later to form a sharper point.

    As built, those strakes don't look like they would even work with 6oz cloth. Did the plans address this at all? How do people usually do strakes like that? I've seen them square, so they must be able to be done. Maybe you were supposed to make them pressed into a square mold off the boat, then secondary bond them on? Maybe a cove should go along that 90 degree strake/hull joint to help transition it better?
     
  5. tomherrick
    Joined: Sep 2006
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    tomherrick Junior Member

    In regard to the strakes, there are no plans for this boat; it's a hull extension. I just built the cores you see of plywood; the originals were of polyester resin putty filler in the mold after the initial laminations were done. It's gonna be a PITA to figure this one out. Generally, I'm thinking that I'll cut out a strip to allow the glass aft of the strake to come together in one lamination and glass over that cut with a solid piece and alternate; but I haven't done this before...
     
  6. pescaloco
    Joined: Feb 2006
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    pescaloco Senior Member

    Some of you outside radius are too hard to get the cloth to lay over and tight
    Vacuum bagging might help you out but I would try a test run on similar shaped scrap.
     
  7. CatBuilder

    CatBuilder Previous Member

    That's your answer for the strakes.

    They were never glassed with sharp edges. They were molded, thickened polyester. You can't expect to get glass around a sharp edge like that, which is why the strakes were made like I was saying in the 2nd to last paragraph of my last post.. by adding them later as thickened resin.

    You should do the same thing - or just seal the wooden ones off with epoxy and be done with it... no glass... unless you plan to beach this boat and need the abrasion resistance.

    And as another thought... how about removing the strakes, glassing the bottom the easy way, then using epoxy to stick the strakes back on above the hull's glass?

    Just brainstorming a little bit here, so take the ideas with a grain of salt. Maybe PAR, who has a lot of experience with wooden boats, will see this thread and tell you how he usually does strakes.

    There has to be a standard way to handle strakes - and it might be to add them later or use thickened resin, like the original builder did. I'm just not a power boat guy, so I have no idea.

    Best of luck...
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    The rule of thumb is, if the strake or rubbing strip is likely to be damaged and absorb water, then there should be a layer of epoxy/glass between it and the hull.

    All plans I have see for boats say to glass the hull, and then apply strips/strakes etc.

    Catbuilder is 100% correct on how to do sharp edges - they are built up over rounded corners, and or thinner cloths
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Strakes as an add on, are a real pain in the butt to execute well, particularly on high speed craft and certain hull shapes, where location and shape can be critical. If it is one of these types, the best thing is to make templates for the strake shape, every foot or two. Rough them in, with heavily eased edges as Cat has mentioned. Try to get the angles about where they need to be, knowing you'll have to go back and build up the edges (corners) afterward. Once the strake is roughed in and 'glassed, use you templates to fine tune the bevels and build up the edges so they're as crisp as the plans suggest.

    The mixture I'd use for the thickened goo edges would be about a 2:1 milled fibers to resin, with a fair bit of talc or spheres to make sanding easier. A touch of silica to control viscosity and you're good to go.

    One trick I've used, is to make a cardboard or light weight plywood dam along the side. This is filled with thickened epoxy, just a bit proud and permitted to kick off or cure. The proud portion is easily knocked flat with the running surface of the strakes, once the dam is removed. This technique also works on transom tops, but you'd use a dam on both sides (packaging tape covered 1/8" plywood, some clamps . . .), fill just proud and let it get hard enough to pull the dams without messing up the thickened goo. With some practice, you can pull the dam(s) and the epoxy is soft enough to easily scrape smooth and flush. When fully cured, ease the edges a touch, so paint can grip it and you're ready for finish work.

    Your strakes look to be more like sacrificial rubs strips to me. If this is the case, then they should be applied after the hull is sheathed and faired. These would be bedded in polysulfide and lightly screwed, to epoxy bonded fastener holes. This permits their easy removal when they get torn up, the bonded holes prevent moisture from getting at the bottom planking and their "add on" nature leaves the hull shell sheathing intact regardless of trailer, rock or beaching damage to the rub strips.
     
  10. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Your radius , both inside and outside, on the strake looks too small for heavy cloth. Some high density filler to build up a larger inside radius will help. The ends of the strake need a tapered wedge shape.

    Heavy cloth...large radius.

    Cutting the strake off is a good option.

    glassing the bottom then adding the strake with overlapping layers of lighter cloth is the way Ive done it . 9oz or 12oz biax conforms much easier when faced with a close inside outside detail

    For cutting pleats at the transome use common sense....sometimes a sheet of brown paper helps to visalise the cuts. A scrap of Biax is the best practice run. The topside, bottom , transom corner is difficult to get right even with light cloth... put a jumbo radius on it. Ive had best luck by not cutting the fabric at the corner, but offset, then forcing the biax to conform

    Also its a good idea to lay the cloth down dry...smooth out...get everything looking good, then take off your work overalls and go home . The fabric will RELAX a bit overnight and manytimes this helps you spot trouble areas before you wet out.

    Oh and I see no biax tape to reiforce the corners ?? The tape adds streagth and increases the radius.
     
  11. tomherrick
    Joined: Sep 2006
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    tomherrick Junior Member

    Thanks all for your insights. A few tweaks on the vacuum system then I can refocus on fiberglass fitting and incorporating your thoughts into my process.

    Thanks again,

    Tom
     
  12. tomherrick
    Joined: Sep 2006
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    tomherrick Junior Member

    Vacuum seemed like the way to go, but I'm apparently too inexperienced to make it work properly. I left plenty of plastic bagging material to accommodate the one-inch lapstrake offsets, it still wouldn't press down the inside corner; it bunched up elsewhere and I wasn't able to smooth it out properly. I don't want to relive all of the frustrating details by recounting them here, but I doubt I'll try vacuum bagging except for flat pieces on the bench.

    The problem is the heavy 1708 material keeps pulling away from the hull - essentially a male form of C-Flex. Yesterday I spent three hours with rollers after laying up about one square yard of material on the side of the hull over the lapstrake offsets and it still pulled up at the corners.
    [​IMG]

    [​IMG]
    It's taking forever for the U.S. Composites' 635 Medium (3:1) epoxy to set. I'm thinking that I'll roll some West System with 205 hardener on the hull and let it get very, very tacky, then roll dry 1708 onto the hull and let the WS epoxy set. After that I can wet out the 1708 in place with the USC 635 Medium. Does this sound reasonable given the materials I'm using? If it works, I may try USC's 635 Fast hardener.
     
    Last edited: Apr 24, 2012
  13. CatBuilder

    CatBuilder Previous Member

    All you can do for a hand layup without bagging is make the corners rounded by putting a cove on them and/or getting yourself some 6oz cloth to take the tight corners.

    Nothing else will work.
     
  14. tomherrick
    Joined: Sep 2006
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    tomherrick Junior Member

    So far, so good. Yesterday, I used West System with 205 hardener, rolled it onto the hull, waited, rolled dry 1708 onto the tacky epoxy and wetted out the glass. Nice results: no puckers, no bubbles, no problem. Today, I used West System with 205 hardener, rolled it onto the hull, then immediately wetted out the glass on the bench, carried it to the boat, rolled it on, added more epoxy, and voila, good results.

    I've ordered the fast hardener from U.S. Composites for their 635 Thin epoxy and will give that a shot as soon as it arrives. For my application, I need an epoxy that kicks more quickly; I can't wait five hours for epoxy to kick so I can stop rolling it out around the lapstrake edges.

    I'll let ya know how it goes with the USC 4:1 hardener.
     

  15. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    You could try laying smaller strips of peelply over the tight edges.

    Sometimes the extra pressure is enough to hold the glass against the tight curve. It saves on finishing time too.

    You would just want to use small .. say 1ft long x 3" wide strips to avoid any puckering.
     
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