Hull fairing questions

Discussion in 'Boatbuilding' started by laukejas, Nov 2, 2020.

  1. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Thank you for your input, guys. Lots of good advice. Let me address what you wrote first, and then I'll show you some pictures where I am now with the fairing.

    I will re-print my spreaders a bit thicker to make them less flexible, then. But I did try them out today, and I don't think that they flexed enough to cause any issues. The whole spreader flexes a bit, but not the teeth, so the resulting epoxy lines are consistent.

    The deck definitely has a compound curvature. It was designed that way. The compound curvature is very slight, but it is there, meant to add structural rigidity to the deck while saving weight on reinforcements, because this deck is only 4mm thick. I'd say it worked, the deck feels rigid like a stone. But the plywood really resisted when I was bending it in shape. Took me a couple hundred of woodscrews (no, I'm not exaggerating).

    I have built two boats before this one. First one, I did not glass. Second one, I did. The first boat was a totally mess after the winter. Major cracks in the plywood everywhere - enough to put a fingernail in. Also disturbing mildew growth. The reason is because our winters can get extremely cold with 100% humidity. I have dehumidifiers everywhere in my garage, no leaks anywhere, and yet there are still pools of water on the floor during winter, from condensation alone. Plywood contracts and expands during freezing cycles, and that causes it to crack. Water gets in, gets frozen, expands, and makes the cracks larger. After that first winter, my boat was pretty much wrecked by the damage that the cold weather did to it, and required major repairs. When I built my second boat, I wised up, and glassed it. No more cracks. I guess fiberglass doesn't allow plywood to crack, for the water to get in, and after the winter, the boat looked just like I left her. No cracks, no mildew.

    That is why I am glassing this boat as well. I put so much work into her, I don't want to lose her to cold weather.

    --------------------

    So, today I had 8 hours of sanding. I tried both dry and wet sanding. 40 grit on my longboard for big surfaces, 60 grit on the orbital sander, and 80 grit on my small plywood sanding pad for detailing. The results are far better than I expected. I must have sanded off at least half the epoxy that I put on last weekend. In some places, I did sand through to the plywood, and to my pleasant surprise, it turns out that epoxy with microballoons that I used as a filler compound has a very similar hardness to plywood itself, and doesn't sand all that differently like I feared. So I continued sanding, removing a little bit of plywood in a few places, but I suppose that's better than having to add another kilogram of epoxy filler to bring all the surrounding areas up a few millimeters. There is just one low spot that I need to fill in, and perhaps a few small gouges here and there. Take a look at these pics and tell me what you think. No hardware stores I visited had any spray paint, so I ordered some from Poland, but until that paint arrives, I made do with pencil lines which you can see in the first photo.

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    Though it may not look like much, it actually does feel very fair to my hand, and no matter what angle I look at my boat, I can't see any irregularities except in that one large low area and a few gouges that I mentioned. In the cockpit, there are far more of them. I am not entirely sure what is the situation down there, and it is difficult to gauge the fairness (and to sand), so I will try to do most of the work with an orbital sander and hope for the best.

    Some of the places do give me trouble. Like the inner edge fillets, where I already applied fiberglass tape. These are not exactly fair to begin with (I did try my best to make smooth fillets and let them harden enough before adding fiberglass tape, but they never come out smooth...) Not sure what to do with them.

    [​IMG]

    One question though. Exactly how much should I try to get that fairness perfect before glassing? Because, after all, adding fiberglass will ruin fairness a bit (fiberglass overlaps, bad corners, maybe floating on a few spots, etc.). And fiberglass does try to remain relatively straight, so do I really need to fill in every time gouge and scratch before glassing? For example, like these little dips:

    [​IMG]

    I will try to catch them all tomorrow and fill them in, but I am pretty sure that once I call it done and get on with glassing, I will still notice a few spots like this that I missed. Do I need to worry about such small imperfections, or will epoxy fill them automatically when I apply fiberglass? Of course I don't want to create voids, but perhaps I can mark these spots with pencil and add more liquid epoxy in these spots when I glass.

    One more question: how the hell do I prevent epoxy from clogging my sandpaper? I did wash everything with hot water and soap before I started sanding to remove amine blush that might have formed on the surface. And yet my sandpaper still clogs. I tried wet sanding. Epoxy turns into this paste that creates a boundary layer between the boat and sandpaper, preventing it from digging in. I have to use my wire brush every few minutes to clean that sandpaper in order to be able to sand again. And worse than that, even when I clean it, it is not the same as fresh sandpaper. It feels like sandpaper just gets dull, even when it's cleaned. Any advice?

    Let me know what you think. Perhaps you will notice some mistakes or anything that I might be doing. And thank you all for helping me.
     
  2. Blueknarr
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    Blueknarr Senior Member

    Looking awesome.
    I'm short on time now and will post more in the morning.

    I would move on to glass npw
     
  3. fallguy
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    fallguy Senior Member

    Epoxy fillers are hard on sandpapers. I generally expect about 2 feet square from a quarter sheet paper. My papers are 50 cents each. The expense is very high.

    I support you 100% on glassing all exposed marine ply. I also experience checking and appearance issues. You will greatly extend boat life with light glass. Do not use heavy glass.

    For inside coves, I use a piece of 1" or 3/4" pipe and wrap it with sandpaper to fair those edges. It is tedious work, but the results are nice. To fill the area fair, find a piece of 3-4mm rubber. Turn the pipe on edge and make a rubber fill tool using the rubber and a vice grip. Move the vice grip closer to the round area until stiff enough. In my drawing, the pipe is imposed black circle and the vice grip blue. Essentially, sand with the same dimension as the fill tool.
    hull fairing question sketch.jpg
     
  4. fallguy
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    fallguy Senior Member



     
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  5. fallguy
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    fallguy Senior Member

    By the way, in the inside tool video, I suggested using a commercial tool. I did purchase a commercial tool, but the tool in the video was used for the entire build as it worked better.
     
  6. Blueknarr
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    Blueknarr Senior Member

    Not all sandpapers are created equal. Some brands have a lubricant that prevents clogging. But you are stuck with what you can get. If you have an auto body - paint shop near by, they can recumend a better sandpaper that is available in your area. That local auto body shop will be a great resource for the next phase of your project.
    The more cured epoxy is the less it cloggs.
    When I have to sand cloggy surfacing, I frequently dust the surface with flour.


    I would:
    Temporally install the deck hardware
    Seal exposed raw wood with neat (no additives) epoxy.
    When partially cured (sticky) spread slightly thickened (mayonnaise) over area to be glassed. This fills surface depressions to prevent them from becoming voids.
    Glass
    1mm fairing compound (mashed potatoes consistentcy)
    Block sand with 80 grit
    Prime
    Sand
    Paint

    You can apply some thicker epoxy to the deepest valleys instead of the mayonnaise. BUT this is a good way to turn a valley into a mountain. Which will be harder to fix than the original valley would have been!
     
  7. laukejas
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    laukejas Senior Member

    Fallguy, Blueknarr, thank you guys, you're awesome. Some very good advice there. I used a piece of pipe and sanded these fiberglassed-taped fillets on the inside corners. When I started digging into the fiberglass, I called it done, even though it's not completely smooth. I just don't want to destroy that fiberglass tape. I think I will add the main fiberglass layer, and once it is cured, I will have plenty of time to play around with these corners until I get them perfect. I will just add extra liquid epoxy to fill in small dips and gouges in the existing fillets.

    So, I got some black spray paint from a local graffiti gang in exchange for some beer. Wonderful stuff. Really brings out these low spots. Using this paint, I sanded the entire cockpit and top deck again, and realized that I won't need a second filling - that first one was enough for me to get a fair surface, even though I dug into plywood in a few places, but not too deep. I went over the entire area 3 times, touching everything, searching for imperfections, until I finally could not find any. Then I de-dusted the surface 3 times with compressed air gun, cleaned it with acetone rag, and laid out the fiberglass. Fiberglass I have is 163 grams/m^2 (that's around 5oz I think?), and it is just 1 meter wide, so it wasn't enough to cover the entire cockpit and the decks, so I had to make some overlaps. Because of the cockpit geometry, it was extremely difficult to get fiberglass in place without wrinkles, especially on converging corners. I had to make some incisions and small local overlaps, especially at the daggerboard box area. After 2 hours of gently conforming fiberglass into shape with a clean brush, I think I finally got it. Then I trimmed the excess and arrived to what you'll see in the pics below.

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    The little wrinkles you see here and there are actually smooth, it's just that I disturbed the weave a little bit. But not too bad. I made sure that cloth can be laid close to the boat surfaces without creating any wrinkles anywhere. The issue is that the cloth doesn't want to stay down on it's own weight. All the cockpit edges are rounded to a large radius, and the cloth can easily conform to them with light pressure. But it won't stay flush on it's own weight. And there are a few places, like that daggerboard case, where I want the cloth to curl around the raised daggerboard case edge and even go on the inside of the case for about an inch or so. The cloth can take that change of direction, all edges are rounded enough. But it won't stay that way, it wants to straighten out.

    I wonder what can I do once I add epoxy, to keep the fiberglass compressed to these surfaces. I do not have vacuuming facilities here. Epoxy should make the cloth heavier, and surfaces stickier, which should help a bit. But I am not sure if it will be enough, because otherwise I might get air pockets in some places. I know that if I wait long enough, once epoxy starts to set, I will be able to bend the lifting fiberglass back into contact with the boat, and it will stay that way. But with these cold temperatures, I might have to wait forever. Not even sure how long. And if I miss that perfect moment, the epoxy will set too much, and I won't be able to push the fiberglass back into contact with surfaces anymore. On my previous boat build, I tried using painter's tape at the edges of fiberglass to make it stay down. Didn't help one bit. Once epoxy gets anywhere near, it immediately un-sticks the tape. And the tape has a nasty habit of pulling fiberglass strands out.

    Any advice? How do I make fiberglass stay flush with the surface, especially near the rounded edges, without having to wait for that semi-cured state to push it back into place if it lifts?
     
  8. Blueknarr
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    Blueknarr Senior Member

    Wet cloth clings better
    Are you familiar with pealply cloth?
    It will reduce the next bit of fairing.
    Staple thru it to hold glass to corners. The staples should come out when the pealply is pulled off.

    Or tacks thru a bit of cardboard. It's not too difficult to sand off the paper. Playing cards work well.

    Beware of tugging cloth out of opposing corners.

    Be sure that all of the base epoxy is adhesion sanded (even if it takes it a bit unfair) before the next coat.

    Remember you are working to YOUR expectations.
     
  9. laukejas
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    laukejas Senior Member

    Thank you, I will probably try staples. Although there might be quite a lot of them needed here, and I won't be able to staple in some areas, like the inside of the centerboard... I am familiar with peel ply. I have called lots of hardware and automotive stores around, and it appears that no one is using it in my country. The cheapest option is to ship from UK, which might take several weeks and cost me a fortune anyway. I searched for ripstop nylon, knowing that some people use it as a poor man's substitute for peel ply, but unfortunately it is not sold in my country either. It is very difficult to get things over here.

    I plan to hot-coat that fiberglass to be able to forgo sanding between layers. Now that I have prepped the surfaces (40 grit paper, then thoroughly cleaned and fiberglass laid down), I will apply epoxy to saturate the cloth, trying to get all the bubbles out, then I will wait 12 hours or so (usually I would wait less, but it's very cold here), and then I will fill the cloth with microbaloon thickened epoxy. Then, 12 hours later, I will add some more, with notched trowel, building up more thickness. Finally, 12 more hours later, I will fill in the grooves with some more thickened epoxy. And then let it cure for a week. I hope that this way I will build up enough epoxy in one go so that I can do final fairing without needing to re-fill anything. It all depends on how close I can get that fiberglass to the surface. I have never fiberglassed anything this complicated before.
     
  10. Blueknarr
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    Blueknarr Senior Member

    Sounds like a good plan.
    Stapling thru cards will make removing them easier. Any left behind might rust thru the finish paint.
    Tacks or brads or finish nails might work where a stapler won't.

    Stuff a wedge into the dagger slot
     
  11. laukejas
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    laukejas Senior Member

    But now I'm thinking... If I use cards and staples, the cards will get stuck to fiberglass, and will have to be sanded off. But I won't be able to sand until I finish all this multi-step process. And these cards won't allow me to fill the weave with microballoons, these cards will get in the way.
     
  12. waikikin
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    waikikin Senior Member

    Just wet through from the top. Best do small areas first. Check out some vids on glassing surfboards. don't put staples in- sometimes you need to stretch and these will pucker your cloth. light cloth down hand is as easy as glassing gets. use a squeegee and a brush when needed. The more difficult area will be the overlap down the centre of the cockpit so fold one side back. Vacuum your floor not the laminate..;)
    Jeff.
     
  13. wet feet
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    wet feet Senior Member

    I agree about not using staples.Even when using them with PVA adhesive for plug building,they often break or leave a leg behind.With the stronger bond of epoxy I would expect a lot more difficulty in removing them.Careful working and maybe a few darts in the cloth ought to get the job done.Peel ply will make it a lot easier to arrive at a good finish in a sensible amount of time.
     
  14. fallguy
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    fallguy Senior Member

    In areas where I have difficulty getting the glass to wrap as I wish, I use peelply and plastic and tape onto a local dry surface. Absent peelply, plastic will work fine. Use 3-6mil and some painters tape.

    You might need to glass that in a couple gos and not a single go. Inside coves and double outside radiuses can be a little hard to get jist right. And more difficult when you try to do too much. Also, access is important. I, personally, would have planned that for two gos to be able to walk in the bottom on one side. But perhaps I am confused on scale. It looks impossible to reach down into the middle from above is all.

    Also, even a good laminator will have some trouble on such a project. You will have some grind out and repair, but the cloth you are using os easy to repair. Grind out air entrained area and lay a new piece and sand flush after curing.

    Remember a couple of tips.
    1. Use a consolidation roller and not a squeegee. I prefer a half inch by 6" bubble buster.
    1. Never run the applicator outwards in coves; only run inward into coves on each side or you will tension the glass and get air pockets.
    2. Never run into outside radiuses. Only run outwards; this will tension the glass and reduce excess glass and bubbles on outside radiuss.
     

  15. laukejas
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    laukejas Senior Member

    Okay, so I guess no staples then. I really wish I could use peel ply, but there's just no way to get it here in sensible time and cost. Is there any other material I can use as a substitute? Fallguy, I did try plastic in my previous build. The thick one from gardening supplies, used to cover plants in winter. But my results were always horrible with plastic. There is just no way to get it smooth, it goes into a wave pattern, and even a rigid roller doesn't smooth them out. And even at that thickness, the plastic itself doesn't really want to conform to rounded edges, so I don't think a thicker plastic would fare any better.

    The boat is not as big as she looks. 1400mm wide (55.1"). I can easily reach the centerboard case when I lean over the side. Here is a quick mockup to show the scale:

    [​IMG]

    Also, I have slightly longer arms than this mannequin :D

    It's just that my clothes start touching the gunwale, which will be fresh in epoxy. I guess I will start working from the inside out, starting with that centerboard, while nothing else is wet and tacky. And if I have to return to that centerboard to tidy it up, I will lay some plastic on the gunwale so I don't get messed up in epoxy. In any case, in these colds, my epoxy has a pot time of around 4 hours, at the very least. So I hope I can manage it over a long weekend. If I see that I get issues at the centerboard, then I will stop there and wait for that part to cure partially before moving on.
     
    fallguy likes this.
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