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Old 12-04-2010, 13:41   #1
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Small Cracks Along Catamaran's Port Keel

my boat was lifted out last October by the same crane that I used for last 4 years without problems . Unfortunately she was dropped onto the port keel from 2/ 3 inches . Iat the time I was placing the timbers on the stbd side and was not even aware that it had happened it was so light . recently I have seen a crack appearing on both sides of the keel , it shows as a moist dark mark at the keel / hull joint . On investigation , today I scraped off some of the copper /epoxy coating on the hull to reveal a fine , hairline crack underneath in the gelcoat ,it is enough to catch a fingernail scraping across it . The keel is 1700mm long and was made as " sacrificial " . I was lucky enough to watch the boat being built at that time and saw that the keels were moulded seperately from the hull and then glassed on afterwards . Now I am considering the route to take ?
As there was a water mark showing through the copper coating it was presumed that it was only this coating that was cracked , but now it looks a little deeper . rainwater washes down the hull and flows on down the keels when on the hard , so this water mark could be from the outside . There is a very small amount of fresh water in that hull as it seeps under the floor from the shower pump , and I mean very small ! . the water marking has only appeared in the last few weeks although liftout was 5 months ago .
I find myself at a crossroads , do I grind back the gelcoat ,etc in the localised areas and epoxy ? or grind back bigger area and lay up using cloth and epoxy ? I am fairly able but not experienced in lay up techniques .
can anyone advise me please ? I want to go sailing , really !
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Old 12-04-2010, 23:47   #2
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You have to scratch out deeper to see where the crack stops. If it goes through the fiberglass you will have to grind it off and redo it.

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Old 13-04-2010, 02:28   #3
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If she has been dropped, the damage may be much deeper and more serious. It certainly should be a high priority to investigate. I would not only be concerned about the keel/hull join, but also about internal bulkheads and mast steps.

Get a surveyor involved - and look more closely at your insurance policy.
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Old 13-04-2010, 11:35   #4
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thanks both , I took jedi ,s advice and carefully ground into the crack and was pleased with what I found . The keels have been fitted to a "stub " moulded into the hulls and are cross bolted through the stub ,to locate , and then glassed inside. the outside crack is merely in the resin fairing and only 2/3rds the length of the port keel . So , the strength and water tightness have not been compromised . My fix will be to soak epoxy into the joint and lay up mat over the whole joint , all with epoxy . then fair and gel sheild and finally , copper coat the lot ! . I would appreciate 2nd / 3rd / .... opinions on my approach ? all advice welcome on this fast learning curve !! , gramos .
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Old 14-04-2010, 09:11   #5
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The question is what the "resin fairing" is. This could be fairing (no constructional function) but it could also be a fillet (constructional). If it is in the corner, making it round, you have to assume it is a fillet and thus constructional. In that case I would grind it all off and replace with a fillet. You can make it a bit tougher by thickening the epoxy with a mix of fillers: 50% micro-fibers for making it tough and 50% colloidal silica to avoid sagging and making it hard. (re)read filleting instructions and wet-sand with paper around something of the same radius. Imperfections will be obvious after that: correct using thickened epoxy with colloidal silica only. Wet sand again, warm it with heat gun and brush the lot with un-thickened epoxy. Let cure for 2 days before finishing with a little sanding and anti-fouling.

If you add glass, you have to do that after replacing the fillet. I would not do it yet because it is a lot of work to fill the weave and fair it out and I don't think a fillet like I described above, with good prep-work, will ever show a crack again.

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Old 14-04-2010, 09:28   #6
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If they are sacrificial keels, then I don't think they would be through-bolted and heavily glassed. That would seem to negate their "sacrificialability" (I know that's not a word).

Mark
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Old 14-04-2010, 13:16   #7
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Originally Posted by colemj View Post
If they are sacrificial keels, then I don't think they would be through-bolted and heavily glassed. That would seem to negate their "sacrificialability" (I know that's not a word).

Mark
thanks, Mark , the 6 bolts found were across the keel going through the stub formed at the bottom of the hull , so only part sacrificial / . anyway , today I laid thickened epoxy into the groove ground out at the top of the stub and 2moro will lay up some csm with more epoxy over the whole joint , 50mm up , 50mm down , to re-inforce the lot does this sound ok ??? working this out with the forumites , on a small Greek Island , where most boats are still made of timber !, .
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Old 14-04-2010, 13:26   #8
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Originally Posted by s/v Jedi View Post
The question is what the "resin fairing" is. This could be fairing (no constructional function) but it could also be a fillet (constructional). If it is in the corner, making it round, you have to assume it is a fillet and thus constructional. In that case I would grind it all off and replace with a fillet. You can make it a bit tougher by thickening the epoxy with a mix of fillers: 50% micro-fibers for making it tough and 50% colloidal silica to avoid sagging and making it hard. (re)read filleting instructions and wet-sand with paper around something of the same radius. Imperfections will be obvious after that: correct using thickened epoxy with colloidal silica only. Wet sand again, warm it with heat gun and brush the lot with un-thickened epoxy. Let cure for 2 days before finishing with a little sanding and anti-fouling.

Nick , thanks , getting this kit is difficult , here , so I have to work with what I can acquire locally , I used some thickened epoxy filler today , is it ok to lay csm over this with epoxy resin ?? at least its warm so it helps with curing ! , I am happy enough that the crack was in a non - structural area , it was in grp fairing about the size of my thumb in width ! se previous post , Gramos .

If you add glass, you have to do that after replacing the fillet. I would not do it yet because it is a lot of work to fill the weave and fair it out and I don't think a fillet like I described above, with good prep-work, will ever show a crack again.

ciao!
Nick.
Nick , thanks , getting this kit is difficult , here , so I have to work with what I can acquire locally , I used some thickened epoxy filler today , is it ok to lay csm over this with epoxy resin ?? at least its warm so it helps with curing ! , I am happy enough that the crack was in a non - structural area , it was in grp fairing about the size of my thumb in width ! se previous post , Gramos .
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Old 14-04-2010, 17:57   #9
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Gramos,

90% of the quality of the end result is the preparation work. When the prep is good, result with almost any epoxy is good while with a bad prep even the best epoxy will fail. So, I wouldn't worry too much about which epoxy you used.

But I get the idea that you just filled up the crack. That is fine when it's just a fairing but I am pretty convinced that it is a constructional fillet. Filling the crack only partly restores it's strength in that case. If you have a thumbs' width fillet on both sides, it might still be a significant increase in surface area.

But as you plan to put fiberglass over it, it doesn't really matter that much. If you can get resin but have trouble finding fillers, it might help that colloidal silica is often sold as CAB-O-SIL and it's also used for concrete or even tooth-paste and soft ice cream. Micro fibers are sold under many names, incl. "cat hairs", "chopped T-shirt" etc.

You will need to find a fairing filler... try to find micro-balloons. Use saw dust if nothing else can be found.

ciao!
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Old 15-04-2010, 13:31   #10
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nick , I ground out all the grp to the hull and keel joint before thick epoxy was added , it took well , next 2 layers of csm and epoxy resin , my aim is to make the joint wider hence stronger , am pleased with the way its going so far ! , gramos
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