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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 05-06-2007
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Carbon + Epoxy and Glass + Polyester

What advice is there for repairing Glass + Polyester with Carbon + Epoxy?
I am looking at a stress induced crack in a GRP hull and am wondering if I can reduce the cut-out and replace scarfing area by using carbon and epoxy rather than the original materials.
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Old 05-06-2007
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I don't know if bonding different resins is practical The harder or softer material. will not flex the same and probably just crack again but this time around the repair. How thick is your hull ? does the crack go through or just surface? The scarf for the repair is 12:1 so if you crack is 1/16 of an inch deep the scarf would be 3/4 of an inch around the crack. If It were me Id stick to doing the repair with the origanal material. And proven scarf deminsions.
just a thought
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Old 05-06-2007
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"The Sound of Boat Maintenance"

Carbon and Epoxy and Glass and Polyester...
Silicone, Stainless Steel Screws, Nuts and Washers...
SEMCO and Sandpaper tied up with string...
These are a few of my favorite things!!!!

Sorry...off topic...had to do it.
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Old 05-06-2007
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SS - I think you have touched on some of the issues. I traced a leak to this crack. It was a bit of an archaeological dig, as three previous owners seem to have addressed the same problem. Early attempts were with glass+polyester and even ended with a bucket of resin being poured in as a last desperate attempt. So now it is my turn and, as the previous attempts clearly failed to distribute the load, I am thinking of increasing strength. I have received recommendations to add inox inserts into polyester+glass, but it seems to me that carbon+epoxy is likely to be stronger and better able to distribute the loads. I am told polyester and carbon don’t adhere well and that epoxy should be used for strength. Conversely, the epoxy fans claim good adherence with everything including carbon.
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Old 05-06-2007
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Quote:
Originally Posted by GotTheNotion
Carbon and Epoxy and Glass and Polyester...
Silicone, Stainless Steel Screws, Nuts and Washers...
SEMCO and Sandpaper tied up with string...
These are a few of my favorite things!!!!

Sorry...off topic...had to do it.
Actually, you raise a valid question: Do SS screws form part of my solution - for increasing the strength of the bond between old and new materials.
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If flexing is the what keeps breaking it then maybe a stiffener or bilge divider glassed 360* would lend enough support to the area. If you did a traditional repair On the exterior of the hull then went inside and put in the stiffener. Maybe you could spread out the load. Have you tried contacting the manufacturer or owners group for suggestions? It may be a common problem. has a yard looked at it?

No need for screws a little cursing and name calling is in order but not screws and bolts
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Old 05-06-2007
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I think we need more information. Size of the boat, thickness of the hull at the problem area, location of the problem area (is it near the keel, rudder or some other stress inducing part?), is the new failure at the interface between new and old material (is so, epoxy might be indicated) or is it at the same spot as the original failure (if so, reinforcing beyond the spec of the original construction might be a good idea) and photos if possible. Generally repairing structural fiberglass with carbon is not a good idea due to the differences in properties between glass and carbon. The carbon patch, being stiffer, will not be able to flex with the original fiberglass which may lead to failure of the bond between new and old material.
It is not usually worth using carbon with polyester resin due to the lower bond strength. Epoxy works well with carbon.
Soul Searcher has some good ideas here.
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one more thing... what is causing the "stress"?
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Old 05-06-2007
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A photo of the area in question would probably also help a lot.

Epoxy resin bonds well to polyester and vinyester resins, and is generally a good material for making repairs. Epoxy resin is stronger than either polyester or vinylester resin in general... which is also good. The only two problems with epoxy resin are its degradation by UV exposure—needs a protective coating of paint, gelcoat or something else—and it softens and weakens at lower temperatures than Polyester or Vinylester resins IIRC...and generally should be finished in a light color if in an area that is exposed to direct sunlight for long periods of time.

You will need to scarf the repair into the existing hull... I would not use carbon fiber for the repair at that point... I would use glass.

If you want to seriously reinforce the area, what you might want to do is after repairing the area with glass, sand the surrounding area for a good distance and then laminate a couple of layers of carbon fiber or kevlar over the whole area.

This is better than using carbon fiber just for the repair, as it will stiffen the whole area. While Kevlar is very weak in compression, it is exceptionally strong in tension and can resist the stress causing the cracking pretty well. Carbon fiber is stronger, and resists compression and tension equally well, but is probably more expensive than the kevlar would be.

I would argue that the SS screws might cause more problems than they solve, since stainless steel expands and contracts at a much different rate that glass, carbon fiber, epoxy, vinylester or polyester resin or kevlar. Also, unless the screws were fully encapsulated in the repair, the screws could allow water to migrate into the repaired area...and if your boat is in an area that the temperatures drop below freezing during the winter, you'd have some serious problems.

Several additional layers of laminate will add considerable strength to the area...but depending on where the problem is occurring may be more trouble than it is worth.
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Old 05-07-2007
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SS- It certainly needs reinforcing inside and out. There are some three functions that the area performs.

1. It has to take the loads on the forward keel bolt, both weight and impact.
2. It has to take the loads of the mast foot down force vs. the forestay leverage plus the hydromanic forces.
3. It has to keep the water out, despite having a hole for the keel bolt through it.

The Coronet owners club only talks about their stinkpots. The builder went out of business in 1977 - this was his last delivered boat. The subsequent builder of Mk IIs also went out of business in th '80s. A yard has looked at it and suggested replacing most of the hull, but I don't think he had time to take on the work.

Ocean - Its a 1977 vintage Coronet Elvstrom 38 (ft) the area affected is between the mast foot and the forward keel bolt.

http://i167.photobucket.com/albums/u...Keelleak08.jpg

The lead keel is below, the fibreglass hull above. I drilled that hole to check how deep the crack was below it. The crack goes all the way through, about 6 cm, to a corresponding crack on the other side. In other words, the base of the hull/keel mount is split across. If you look carefully, you can see the keel bolt, just aft of the hole. Note also the signs of repair attempts including angle grinder scores in the lead keel and the multiple flexure cracks in the anti-fouling above.
How thick is it? Well that is a bit difficult to judge from the repairs. I think the hull sides started at about 1 cm and the foot at about 2 cm - so I am not surprised at the failure. Obviously, I dug further.

http://i167.photobucket.com/albums/u...eelcrack33.jpg

Now you can see a previous glass+polyester repair. The crack was found to have travelled higher, so I drilled again to find out where on the inside the crack was. The upper hole is at about the backing plate level. After initial digging on the inside it looked like this.

http://i167.photobucket.com/albums/u...elbolts017.jpg

I had to drill and chisel down through one layer of glass and 20 cm of resin to reach the keel bolt/nut. That bucket of resin had stiffened the area, but not enough. I don't have a later stage picture, but I chiseled out all of the resin, it had not adhered well to two further glassing jobs further down. OK found a later picture:-

http://i167.photobucket.com/albums/u...keelstud01.jpg

Basically, the entire bending forces get concentrate on that stud and its tiny backing plate. It can hold it, but the surrounding structure needs to be stronger.

SD - If I used glass and then carbon, surely the carbon, being less elastic, would have to take all the load? So the stress would still be on the polyester to epoxy bond.

Last edited by Idiens; 05-07-2007 at 09:16 AM.
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