Looking for advice on Keel repair...

[pcmm]

Originally Posted by NahanniV

Just wondering. With the rig off the weight of the boat is reversing the forces.

So, are you saying just do the repair as it sits ?

Thanks,
JM.

you need to grind out the crack a bit to get back to clean uncontaminated glass. then laminate up the repair from the outside and then from the inside. I dont know why one poster recommended that you use plastic film to keep the air out as keeping the air out has nothing to do with the curing process unless you are using polyester resin ( not recommended for structural secondary bond repairs)

How thick is your hull at this point? you need to grind a 12-1 taper into the damaged area for maximum strength . FYI 1/2"thick fiberglass is about 12-13 layers of biaxial glass so get yourself a pair of electric rotary scissors they make cutting out the layers of glass much easier.

[four winds]

Originally Posted by hamburking

Your pictures and description of the problem, and your determination to solve this leak are all very impressive. Thanks for documenting it so well, and sharing with the rest of us.

Absolutely. Impressive is a good word to describe the OP's troubleshooting here.

Excellent post.

[pcmm]

Originally Posted by chris95040

The bond strength of a repair is no where near the strength you get when the polymer is crosslinked throughout the structure (which is the case with new builds.)

You are right that the actual repair material, if made in polyester, will be similar in strength to the rest of the boat.

Its that the attachment of this repair material to the rest of the boat will never, ever, ever be as strong as if it were chemically crosslinked to it. We work around this by having huge bevels to maximize the contact area the repair has with the surrounding hull.

Another thing you can try to maximize is the bond strength of the repair to the hull. That's why people use epoxy, because it's superior to polyester in this regard.

Adequate bevel or not, that repair interface will always be there, and especially in this case where the repair area is loaded by the rig, I'd feel comfortable maximizing my bond strength so that the repair doesn't slowly tear / work itself out.

But in the end, I bet you are right. Polyester would probably be more than adequate. I'm just armchairing / explaining the rationale for using epoxy (which I would definitely use in this case.)

In most cases Epoxy is far easier to work with than Polyester. longer working time and much simpler to mix in the correct ratios. It is however a bit more expensive than quality Polyester resins.

[Don C L]

Originally Posted by NahanniV

Just wondering. With the rig off the weight of the boat is reversing the forces.

So, are you saying just do the repair as it sits ?

Thanks,
JM.

I am a little confused. Just reconnecting the rigging now won't change things. The rig under pressure, while sailing, was lifting the hull away from the keel, opening the crack, I gather. While re-pressuring the compression post recreated that (which in itself is a little surprising to me that you could apply that much force!,) you could ask the yard to lift the boat and let it hang on the slings to see what will happen then. I would hope there would be no change to the hull, keel and keel root, and the crack. However I have seen boats where the hull does flex as it rests on the keel, and un-flex as it lifts up. The flex is not a good thing to see but not uncommon. To me cracking through the hull is worse, if the crack you have is related to the weight of the ballast pulling the leading edge of the keel down in addition to the compression forces. As far as whether it should be repaired with pressure off the keel or on, my inclination is off, if possible, but that would mean letting it hang in the slings for quite a while to let the repair cure! In your situation (as with most boats with keel stepped masts) the weight of the ballast and the compression forces conspire to try to separate the keel from the hull. In my boat, granted much smaller and much lighter, I have encapsulated lead too. But the root of my keel is wider and shows no deformation whether hanging or on the hard. I have never seen a Finnsailer so I may be way off, but it just appeared to me that the keel root was quite narrow for a keel that is not bolted on. That makes the original construction of the hull at the keel root all the more important and hopefully very thick. I don't want to flog a dead horse, and I hope some boatbuilders out there will correct me if I am wrong, but I think it might be wise to look into putting compression forces on the hull and not the keel to avoid another crack in the future. Don't get me wrong, I definitely don't see the keel falling off!

[Don C L]

Really curious how its going and what you decided to do with it. Any news?

[NahanniV]

Originally Posted by Don C L

Really curious how its going and what you decided to do with it. Any news?

Got the material for the compression post base. Cut it to size.
Need to pick up the bolts and nuts.

Need to pick up BiAxial cloth, 406 filler, watertite epoxy filler, solvent wash.

Will try to finish grinding the area this weekend, but it may not be warm or dry enough to do the patch.

My plan is to use only BiAxial cloth on the outside. 3 or 4 layers at a time.

Would peel-ply work on this surface ? Maybe too many curves ?

I have some heavy woven roving that I may use on the inside after I build up a few layers (12-16 ?) of the BiAxial.

[jimbunyard]

Originally Posted by NahanniV

Got the material for the compression post base. Cut it to size.
Need to pick up the bolts and nuts.

Need to pick up BiAxial cloth, 406 filler, watertite epoxy filler, solvent wash.

Will try to finish grinding the area this weekend, but it may not be warm or dry enough to do the patch.

My plan is to use only BiAxial cloth on the outside. 3 or 4 layers at a time.

Would peel-ply work on this surface ? Maybe too many curves ?

I have some heavy woven roving that I may use on the inside after I build up a few layers (12-16 ?) of the BiAxial.

Remember that the strength of the repair is solely dependent of the bond of the epoxy coupled to the existing hull.

If you're gong to put 16 layers of biaxial (what weight?) on the outside without feathering it into the existing hull, as a kind of armor against future impacts, well and good (though I'd be leery of introducing stress points at the periphery of the 'armor' and the existing skin), but if you're going to grind the hull down to the often specified 12:1 taper, you'll be seriously compromising the hull in that area by removing the strength inherent in the continuous longitudinal and transverse fibers of the original roving, and substituting that strength for purely the bond strength of the epoxy to the polyester resin.

A sketch that may illustrate this is attached, it is drawn as a flat plate for clarity, the small shaded rectangle in the center represents the (not to scale) crack in your hull now, the cross-hatched area shows the amount of glass you'd remove for a taper about 3:1 transversely and 6:1 longitudinally. The whole plate represents the size of the area that you'd be relying on the strength of the epoxy/polyester bond only, if you were to grind off the existing glass (the real strength).

I've only used peel-ply in conjunction with vacuum bagging, which might be a good idea in this case if you can rent or borrow a pump, but it's not really necessary for such a (physically) small repair. If you do vacuum bag it on the outside, you have to repair the inside first (which you should do anyway).

[NahanniV]

Originally Posted by jimbunyard

Remember that the strength of the repair is solely dependent of the bond of the epoxy coupled to the existing hull.

If you're gong to put 16 layers of biaxial (what weight?) on the outside without feathering it into the existing hull, as a kind of armor against future impacts, well and good (though I'd be leery of introducing stress points at the periphery of the 'armor' and the existing skin), but if you're going to grind the hull down to the often specified 12:1 taper, you'll be seriously compromising the hull in that area by removing the strength inherent in the continuous longitudinal and transverse fibers of the original roving, and substituting that strength for purely the bond strength of the epoxy to the polyester resin.

A sketch that may illustrate this is attached, it is drawn as a flat plate for clarity, the small shaded rectangle in the center represents the (not to scale) crack in your hull now, the cross-hatched area shows the amount of glass you'd remove for a taper about 3:1 transversely and 6:1 longitudinally. The whole plate represents the size of the area that you'd be relying on the strength of the epoxy/polyester bond only, if you were to grind off the existing glass (the real strength).

I've only used peel-ply in conjunction with vacuum bagging, which might be a good idea in this case if you can rent or borrow a pump, but it's not really necessary for such a (physically) small repair. If you do vacuum bag it on the outside, you have to repair the inside first (which you should do anyway).

I am thinking of getting 1708 cloth, my understanding is 4 layers is approximately 1/8". I have at least 1/8" of filler already removed from the exterior. I'm not sure how many layers I will add to the exterior, my comment about 12-16 layers was about the inside, where I plan to add most of the strength.

[jimbunyard]

With 1708, maybe 4-6 (.2-.3" thick dry) layers on the outside and 8-12 (.4-.6" dry) on the inside?

[HappyMdRSailor]

Originally Posted by NahanniV

The area with the crack is quite sharp and thin, the leading edge of the keel gradually gets more of a blunt round shape further down, so I think I could actually add some layers and still be able to fair it.

What a fantastically well documented failure ! I think you're on the right track with the 1708, epoxy, and lots more grinding...

The above quote was included because you really can get creative with the outside profile of the keel root changing to accommodate whatever layup That would make everybody confidently happy! Me??? I'd be 1/2" over what was there before, but I'm a worrier...

Honestly.... with this much work, and this major importance I would get our resident genius minaret involved... If there's ever been a repair on a boat... He's done it... more than once!

I'll send him a PM with the link here for you...

[jimbunyard]

Originally Posted by NahanniV

Thanks for all the input !

One question I have is if I should tension the chainplates and possibly put an extra jack stand under the bow of the boat during the repair ?

Cheers,
JM.

I've had the same question sometimes when doing similar repairs, but I tend to trust the stiffness of the hull as built unless something was flopping around or obviously misaligned (and I wouldn't introduce more stresses by aligning it). Beyond well supporting the hull at the keel and with jackstands or cradle (as appears you have in your pictures), I always come back to glassing it as it sits. The reasoning is that the possibility of me duplicating the in-the-water shape of the hull on the ground by any means is virtually nil, and I wouldn't know it if I had, anyway.

The intersection of the keel and the hull looks fair in your pictures, I'd glass it as it sits.

[Don C L]

I am curious to know if you notice any flex in the hull aft of the keel while it is on the ground as opposed to when it is in the slings. I too am of the opinion that the patch may not be as strong as the hull as it is even now. I hope Minaret will have a look too!

[NahanniV]

Originally Posted by Don C L

I am curious to know if you notice any flex in the hull aft of the keel while it is on the ground as opposed to when it is in the slings. I too am of the opinion that the patch may not be as strong as the hull as it is even now. I hope Minaret will have a look too!

No I don't see any distortion or cracking anywhere else in the hull. I had a particularly thorough look near the aft end of the keel since I read that that area can also be damaged in a grounding.

[HappyMdRSailor]

Originally Posted by NahanniV

No I don't see any distortion or cracking anywhere else in the hull. I had a particularly thorough look near the aft end of the keel since I read that that area can also be damaged in a grounding.

Good news on no further damage and ... Indeed on point 2.

No minaret yet, sent him a PM for you, but he must be swamped... usually he jumps, but he is running his own yard so... hopefully we'll get his input soon enough!

[NahanniV]

Originally Posted by HappyMdRSailor

Good news on no further damage and ... Indeed on point 2.

No minaret yet, sent him a PM for you, but he must be swamped... usually he jumps, but he is running his own yard so... hopefully we'll get his input soon enough!

Ok, I'll bite. Where did you get that picture from? Looks worse than mine. Did they fix it ? How ?

Cheers,
JM.