How would you repair this hull damage? - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 05-06-2009
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How would you repair this hull damage?

I have a 1974 Coronado 41. Ever since I've had the boat, there has been this one poorly repaired crack through the hull that has bothered me. I assume it was just patched with some kind of surface expoxy/filler mixture because the damage was by a window and they didn't want to take out the window to repair the fiberglass.

I now have the windows out (they needed replacing anyway) and I can't let myself reassemble the windows without fixing this crack. The crack is about 4 inches long and goes all the way through the hull laminate and also went through the interior cabin liner. There are some stress rings above the crack which I have to dig into and see how deep they are - hopefully not all the way through the laminate. The deck is solid 1/2" vinylester layup so I won't have to replace core.

I have done some vinylester lay-up repairs in other places but usually in areas where there's a hole or such that the mat can be installed in an all-around beveled area. I usually follow the very basic procedure by Don Casey for fiberglass repair: Fiberglass Repair by Don Casey

But with this one I am wondering if there is anything different to do since the damaged area is right up to a window frame. I plan to cut out a somewhat circular area around the damage and bevel it towards the inside of the boat. I will have to cut out an even larger circle on the headliner on the inside to get access. I plan to stick a plexiglass sheet with mold release against the outside of the hull with some kind of flange to match the window curve and lay the mat into this shape a few layers at a time wetted out with vinyl ester resin. I don't know if I will gelcoat it since it is mostly in this blue area which I had painted in the past.

When the hull repair is complete I can re-build the liner and gelcoat on the inside.

Does this sound like a good approach, or does anyone have suggestions of a better way?

Thanks!
Cosmo

Crack in the upper right corner of the window:


Close up from the outside:


Sort of cross section:


Crack from the interior (I'll need to remove that bookshelf above I guess)
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Old 05-06-2009
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what i would so is to bevel out the crack with a sanding disk on a grinder. take it about 1/2 way thru. with the bevel out to about 6 inches out side the crack. then rebuild it just like the west systems fiber glass repair. then go to the inside and do the same. you could go to 3/4 the thickness from the out side and taper it 6 inches to, so you dont have to do as much inside. or vice versa for less work outside

then fare it on the out side with light weight filler, and you should also use epoxy, not poly or vinyl esters.

done right its about 4 to 6 hours per side, in 2 2 to 3 hour shots then faring

edit lust looked at the pics again, i would grind out the whole crack and just leave enough glass to give you the shape and fill with fiber glass from there but you will have to taper it out 10 to 12 inches, then do the same with the liner

Last edited by scottyt; 05-06-2009 at 03:55 PM.
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Old 05-06-2009
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I'd go pretty much the way Scotty mentions, but I would use a saw and cut the crack all the way through on both outer shell and liner, so there was a slice cut through it.
Then bevel the edge out a ways and slip a chunk of plastic wrapped plywood or a chunk of plastic cutting board in there to act as a backer while I layed it up. That way you have something solid to hold it in position, and you get rid of the frayed area that could cause difficulties.

I don't like to just press a ragged edge together while I repair, getting the crack cut out makes for a much smoother and stronger repair, that will be easier overall.

Ken.
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So you both think I should taper and apply the repair mat to the hull section from the outside vs inside? And favor epoxy (for strength) over vinylester even though the hull was laid in vinyl? I figure I don't need to gelcoat the blue section, but I will probably cut into the white gelcoat above (especially if I taper outside) and since I am new to color matching and gelcoat I will have a better chance of it looking good if I use vinylester. I would just tape off the section of "white" repair and gelcoat and finish that part while painting the blue part.

I do like merc2dogs' idea there of sticking a plastic wrapped/ pva coated block of plywood into the void between the hull and liner while doing the job. That would require me to work from the outside anyway.

Don Casey suggests tapering and working from the inside, is the main reason for that to make the gelcoat press against an outside mold and therefore result in less gelcoat finishing work?

I guess also if using vinyl ester I have to have that air tight seal or use plenty PVA while I won't have to worry about that with epoxy.
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i agree with ken, as i would not press it back together. i would grind it out except 1 layer of glass to hold the shape. also grind it out till you hit solid glass then do the taper
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you will never match the gel coat perfect, but what you can do is do the repair with epoxy, as it will be a much much stronger repair. then where its white after it fared do a couple of coats of gel coat rolled on with a roller. when the repair is hidden by gel coat, mix up a tinted coat and roll that, if it matches sand and polish it, if it does not mix a different batch and roll an inch farther, keep repeating till you happy with the match. this also will let you blend it better by wet sanding with 600 grit. luckly gel coat cures quick

btw where are you located
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Old 05-06-2009
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Couldn't he tint the epoxy? That might be easier than getting gel to adhere to the epoxy, wouldn't it?
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he could but it wont look right and epoxy is not uv protected. he could tint it to get it closer so he needs less gel coat to cover it. and gel coat over sanded epoxy will stick well enough for cover reasons. it will stick as well as using polyester for the repair, which is not near as strong as epoxy will
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Structural repairs like this really need to be done using EPOXY resin. These kinds of repairs rely primarily on the secondary bonding characteristics of the resin, and epoxy has much better secondary or adhesive bonding characteristics.

Given the damage shown, I would grind it out to a 12:1 bevel for the thickness of the glass, which isn't a whole lot.. a radius of maybe 4-6 inches from the damaged area.. doing any more than that is just making the job a lot harder.

Gelcoat will stick to epoxy resin, provided the resin has been properly cleaned and prepped prior to applying the gelcoat.

A thin sheet of HDPE will work to separate the liner from the hull, and epoxy doesn't stick well to HDPE, so a coat of mold release on it should do the trick.
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Great, thanks for all the advice! I will post pics of my repair if you promise not to laugh As always on this boat the goal is primarily "better than it was before" and that's usually not hard to do

I'm in Seattle and we have really lovely weather now for boat work (not!) don't believe the blue sky in the top photo... The day after I pulled the windows we had a gale with torrential rain (that was Saturday) and another one yesterday. Now it's just rain, but there's a glimmer of hope for the weekend.
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