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Bond fiberglass sheet into topside cutouts?

Joined
21 Apr 2017
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74
I am thinking of downsizing my large through-bolted plexiglass windows to portholes. Ready-made fiberglass sheets or panels sound like an attractive way to fill in the cutouts quickly and cleanly, but could I bond sections of sheet into the topside window cutouts as strongly as laying up laminate by hand?

I think stiffening stringers on the inside would be a good idea. Perhaps the new sheet and existing laminate could be beveled so that the sheet is applied from the outside and screwed onto stringer cores made of a strong material and extending onto the existing laminate, clamping the sheet into place in addition to any bond around the edges.

Ideas?

Code:
        |  O|
OUTSIDE \  L| _
       |\\ D||#|
       | \\ ||#|
       |N \\||#|       INSIDE
       |E  \ |#|
       |W   ||#|     screwed to
       >=====|=|  <- stringer core
       |    ||#|
         ...
       |    ||#|
       |   / |#|
       |  //| -
       | // |
       |//  |
        |   |
 
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Javelin

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How are you going to hide the edges of the sheet outside?
I doubt the edges will be gelcoated.
 
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Topside paint throughout I think! Gelcoat is tatty and I'm ambivalent about cosmetics. The edges would be faired in with epoxy as appropriate.

It's really the strength of the bond that I'm concerned about.
 

Javelin

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On that basis epoxy stringers on the inside.

I would find somthing shiny and flat and tape it to the outside and then gelcoat and layup against it from the inside.
If I want stiffness I'd use a core of 10mm foam or honeycomb or at worse ply.
 
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Thank you, could be less of a faff than painting.

Does it matter which way around the bevel is? I thought that if the new laminate overlaps the existing laminate from the outside then any sea it takes pushes the bonded area together, rather than apart (if I was laying up from the inside).
 

prv

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If done properly, the bond should be strong enough to make that concern irrelevant.

One reason to come at it from the outside, though, is that the proper shallow taper needed to make that bond means that something as large as a window in full hull-thickness fibreglass will mean a *very* large area to the repair. I can imagine that needing a lot of joinery stripped out on the inside, whereas on the outside you have smooth hull all round to work with. Chucking tons of grinding dust around outside instead of all over the accommodation is a nice bonus too.

I don't think the pre-made sheet idea is a good one, because it won't conform to the ground-out taper on the existing hull laminate in the same way that wet mat pressed down with a paddle roller will. Unless you can make joints in polyester the way Leo from Tally Ho makes them in wood, you're going to end up with a layer of unreinforced resin between the two, and that's a serious defect in a hull.

If the window to be filled was truly massive then you could perhaps taper both ways (hull laminate one side, sheet GRP the other) and fill the valley with mat and resin bonded to both. But it doesn't really seem worth it compared to the conventional repair with all wet layup on a waxed board pushed out into the hole from the inside.

Pete
 

prv

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It's just occurred to me that you're probably talking about windows in the coachroof



rather than the topsides:



!!

That does seem a bit more amenable to DIY GRP work than what I was picturing. I was politely refraining from saying "are you sure you're up to filling major holes in the side of the hull?" :)

Pete
 

convey

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Are the sides of your coachroof entirely flat? Which boat are we talking about here?

I'm interested as it's something I've considered doing as well but it turned out mine was subtly and complexly curved in both directions. I concluded I could make them match those curves by doing what was advised above, that they'd flatten out irregularly.

If visuals are of great concern, why not just cut and drill the glassfibre sheets to the same oversize as the current panes, and bond as usual, then fit the portholes in them? There's no way you'd manage to cut a perfectly matching bezel.

I've actually seen someone do just that with ply creating what I thought of as a sort of "frogeye" effect. It didn't look too bad. It strikes me it could be difficult to end up with a "perfect" finish, so why not make a feature out of the hack instead? Certainly would be cheaper and quicker. You could even use a contrasting colour of sheet, eg black or orange, in a sense, hiding the edges by making them stand out more.

If you went the way of grinding a bevel, laying up by hand, you'd need to fill all the bolt holes.
 
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Sorry Pete, I was talking about the coach roof. Thank you for your patience.

I see the benefits of laying up fresh laminate, so that answers my question.

convey: that had occurred to me and I'm generally for making a thing of the hack. It's a small boat (Sunstar 18) and the coach roof isn't flat in at least one plane. One thing that I want to get out of this is less sealant to maintain, as well. Filling bolt holes shouldn't be a problem.
 
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lw395

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I assume the clear panels of the windows are not structural?
And that they don't have great structural frames which reinforce the coachroof?
In which case, the window infill panels don't need to be particularly strong. They need to be strong enough to resist the sea, but they don't need to support the coach roof.
Tapering the outside of the existing window apertures much could be a big mistake, as that is possibly the major reinforcement of the coachroof.
How thick is the moulding at the edge of the aperture?
How is the interior of the coach roof finished? Will you be able to cover the joint?

If you can simply tape over the joint inside with several layers of mat, tapered to say 3mm thick over the actual join, that should be much stronger than the few screws and bit of sealant which currently hold the clear plastic in place?
But there's some work in hiding it behind headlining...

TBH if the whole thing is driven by problems with sealant, I'd reconsider. Make a proper job of bedding the windows and it should be good for 10 years.
 

Spirit (of Glenans)

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Are the sides of your coachroof entirely flat? Which boat are we talking about here?

I'm interested as it's something I've considered doing as well but it turned out mine was subtly and complexly curved in both directions. I concluded I could make them match those curves by doing what was advised above, that they'd flatten out irregularly.
If the existing windows are curved, they will only be curved in one plane. The flat shiny material will follow that curve, and any surrounding compound curvature will not be affected.
 

convey

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Not in my case, they curve vertically and horizontally. It made/makes fitting portholes impossible without flattening them off, or counter sinking them. It wasn't a lot, from memory a 1cm or so at either end, but enough make it look poor without depending on a lot of Bondo.

But, I agree, in most boats it will probably just be horizontally (along the line of the keel).

I'd like to see or know the OP's boat. A lot of boats use a long, singular piece of acrylic over a series of apertures in the mould to create a styling effect, eg Newbridges, some Achilles, many high end motorsailers, I think the Macgregor 26s. It could work. If you've got two or three apertures and fit one long piece across them, it's got to make it very strong and general experience says that sealing is not a problem.

I don't know the relative prices but it might open the door to solid coloured plastic sheet. Lexan is bulletproof.

But, if the intention is to create something that looks like a stock finish, then the laying up from the inside method above is the way to go.
 
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Again I'm not fussed about cosmetics. This is a Sunstar 18 (not mine): https://boats-from.co.uk/sites/default/files/products-images/2017-07/65676/65676-59027.jpg

But my windows are thick plexiglass sealed and bolted from the outside, so that the side windows span both cutouts. I haven't got dimensions to hand but I think they're thicker than the laminate.

I have a lot of things to do on this boat that are a higher priority, but replacing the windows with portholes has been on my blue sky list because of the amount of time that work on these windows takes (due to the sealant and number of bolts), the large area that can develop leaks, and their tendency to scratch. I also like the idea of having a standard window for maintenance.
 

convey

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The link is broken but are you talking about one of these? Front ones look as if it would be a bugger to do. Side one's pretty flat. Were the older/original models like this blue one? That looks like the same rubber seal I had.

I see the early Leisure 17, from it appears descended, had one front circular porthole and one long oval at the rear. That gives you an idea of how it would look.



 
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That's the one! I didn't expect this thread to generate this much interest!

The front windows wrap around at the sides and there is a stiffening stringer between them and directly above and below laterally. Bugger yes!

Same designer as Leisure 17---the differences are minor. The Leisure Owners Association says of the plexiglass bolt-over windows (in the newer L17SL) that they make a very tough window. I'm not in any rush to get rid of them, but every time I think about the boat it's there in my long term plans.
 

convey

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We are here to help our brothers and sisters of the sea.

I think if you want to do it properly, and it would not be impossible nor that expensive given it is an 18'-er, you would be best to make a female mould of the cabin top, fill it up and smooth it off to where you want to get to, then fibreglass the original shape in from the insides. Especially if you are talking about doing the front 'lights. Side 'lights you might just get away with using flat pieces of plastic and releasing compound.

Or buy a different boat.

Depends how married you are to this one.

I'm guess the original front 'lights are no longer available, nor are the original moulds, so that make make it worthwhile. It is possible to bake acrylic/polycarb in the oven and bend it into shape, but a gamble.

What's "the big plan"? Are you planning on sailing across the Atlantic in it or something?
 
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prv

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Now that I've got a better idea what we're dealing with (not your fault, I jumped to conclusions) I'd be a bit more relaxed about strength. Especially those rubber-edged windows in Convey's pictures, those'll be adding nothing to the coachroof structure so it clearly doesn't need any help. I think it should certainly be possible to glass in GRP panels more strongly than the rubber and probably the bolted windows - though I'd still go for wet layup of the joint, either with edges tapered away from each other if you want a smooth result, or just butted together and glassed over the top if you're doing it from the inside and don't mind a ridge around the edge of the old holes. Or indeed lay up the whole thing in place as Convey's suggesting.

Pete
 
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In reply to both: I have the plexiglass pieces, so I imagined that laying up from the inside could be done against those + releasing cloth, if enough bolt holes are located far enough from the edge (gotta check).

Big plan yikes! I'd like to sail the boat at some point! The boat came to me quite damaged, so I've gotten used to the thought of lots of big tasks. I hope after all this that I like sailing.
 

convey

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One last thing. If you're going to replace the two front 'lights with round portholes, you've got to give it two painted eyebrows.

1593635411498.jpeg
 
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