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Old 12-17-2008
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Dropping the Keel

This looks like the sort of place where there are people that will know about dropping a keel.

I am looking advice on dropping a fin keel to inspect the keel bolts.

Background
I have a small crack in the keel which may go beyond the gel coat. There are no internal leaks from nuts, but I have decided it is time to check the keel bolts and fix the crack and also re-fare the bottom of the boat and keel at the same time.

I have seen a keel dropped and reattached before and the process looked fairly simple, provided you have a crane that can lift the boat. Searching the net for other methods used include creating a frame to support the boat in a fixed position and a separate frame to lower the keel into, but then maneuvering the keel back on might be more difficult.

To get an idea of the size of the project the boat is a 40 ft fiberglass mono hull with a fin keel attachment. The keel bolts are in line and there is what is called a deadwood stub (glassed) below this there is an external lead keel. The stub and lead are joined as one, i.e. you cannot see the join. The crack is between the stub and the hull. The keel proportions are the same as the Farr 12.2 meter.

Questions
So my main question is once I have dropped the keel and checked everything is OK with the bolts and come to be reattaching the keel what adhesive should I use? I have read and heard different things, i.e. that there are special glues/sealants that are extremely powerful that are used to attach keels. One rebedding compound that is mentioned quite a lot in relation to keel bedding is 3M 5200. There are probably others...?

Another method also used by others is to epoxy mixed with micro-balloons or perhaps chopped glass fibers to produce a sort of paste that has a consistency somewhere between peanut butter and honey (call this "epoxy paste").

Some people also recommend adding "Pentamid" to the epoxy to make it more flexible, but not sure if I want any flexibility at all. Perhaps epoxy with Pentamid could be used to fair around the join after the initial epoxy sets. However then regular epoxy and glass cloth would go over the top of this to build up the support around the keel by an inch or two (hopefully not having a big effect on performance.)

Application
Anyway using whatever mix (epoxy paste, 5200) decided on apply this to the cleaned, dry roughened surfaces on both the boat and the top of the keel. Then lay a smooth mound of the mix on top of the keel in the middle running fore and aft about an inch or more high. This mound will push out any air as the keel and boat come together.

If I used straight epoxy paste, I have been tossing up another additional protection against future cracks and leakage, but have not seen any it done anywhere else. I was thinking that I could use 5200 (or epoxy+Pentamid) in a small ring around the actual bolts and epoxy paste everywhere else. The idea is that if the epoxy cracks the 5200 being flexible will still provide a seal to prevent water access to the bolts and therefore any galvanic corrosion. I am not sure exactly how this would work in practice.

Then lower the boat onto the keel, do up the bolts (not one at a time but using a pattern). I think the the bolts then should be retorqued (using a torque wrench) to the same average toque as before they were removed. The retorquing the bolts needs to happen while the boat is still on the hard and with boat sitting back on the keel and other supports. The question here is that when the boat goes back in the water the keel will be pulling down rather than pushing up, so perhaps the boat needs to be support and some weight taken off the keel when retorquing the keel nuts. In any case the important thing in this phase is to not have the boat wobble or move before the rebedding adhesive is set. If the boat does move you could end up with a gap. But easier said than done, any ideas?

After the keel is set clean the excess epoxy paste away and wait a day or so before fairing in some new glass around the keel base. At this stage I was thinking of building up the base of the keel so the join was a bit more rounded and better supported so the keel is less likely to crack again. To do this I would sandblast to remove the gel coat around the keel and build up layers of epoxy and cloth cut to cover an increased area with each layer.
different thickness. How can I get heavy cloth to stick when applying it to the bottom of the boat? I am guessing apply a coat of epoxy wait till it starts to go off and lay the cloth on top, then paint on some new epoxy before the initial coat completely sets.

Does this sound reasonable?

Many production boats are shipped with keel unattached and it is then reattached on arrival. So I am wondering what technique and adhesives are used in these cases?

Anyone had any experience with this?

Last edited by matt2; 12-17-2008 at 08:16 AM.
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Matt—

First, it would help if you said what boat you have, as there may be issues specific to the make and model of boat you've got.

Second, not a good idea to use epoxy to re-bed the keel, especially, you'll probably have to drop it again in the future, and bedding it with epoxy will make that really an interesting, in a bad way, task.

Third, 5200 isn't necessarily the best choice of sealants to use. 5200 has an adhesive strength greater than the underlying laminate and is very difficult to remove, again causing any future re-bedding to be more interesting than it should be. It is also not as elastic as some of the other sealant, that might be better suited to the task.

You should also inspect the keel bolts for any corrosion damage, since bolts that have sat in salt water for extended periods of time can easily be eroded away by corrosion.

in your Application section, I believe you mean KEEL not RUDDER. Bonding the rudder to the hull would be a bad idea generally.

BTW, most hull-keel joins are faired, but not glassed over. Glassing over the join can seriously complicate repairs.

I'm sure that Maine Sail will be along with his recommendations on what sealant to use, probably SikaFlex 291 or something like that...

I'd highly recommend you read the POST in my signature to help you get the most out of your time here. It has tips on searching sailnet, writing a good post, etc.. Welcome to the asylum.
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Old 12-17-2008
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Ok thanks for the response, very helpful.
Quote:
Originally Posted by sailingdog View Post
First, it would help if you said what boat you have, as there may be issues specific to the make and model of boat you've got.
The boat is non branded, but is essentially an exact copy of the Farr 12.2 m design at least as far as the Hull and keel are concerned. This is an 1980's fin keeler with a modern hull form for that era, but built quite heavily i.e. as a cruiser not a racer. The keel is about 4 feet high and about 10 inches wide at the widest point. The top of the keel is about 6 feet long and the bottom is about three feet. Sort of looks like a wing tip. Not sure what else I can say, I don't have any photos with me. I have owned the boat for 10 years and do all my own maintenance. I have experience with fibreglass, epoxy etc, e.g. successfully re-glassing the rudder.

I have talked to shipwrights about this, but I get different suggestions, some say use a sealant and some say epoxy and then glassing over the keel-hull join.
Quote:
Originally Posted by sailingdog View Post
Second, not a good idea to use epoxy to re-bed the keel, especially, you'll probably have to drop it again in the future, and bedding it with epoxy will make that really an interesting, in a bad way, task.
But surely a flexible sealant will let the keel move and will crack any faired surface almost immediately. i.e. a faired surface has no strength and is quite brittle, unless the additive can make it flexible? The boat sits on the keel when being slipped, so there will be some flexing.

I do see your point, if the epoxy path didn't work it could be difficult separating the keel and hull again.

Do you happen to know what boat importers use for boats shipped by container with the keel detached?
Quote:
Originally Posted by sailingdog View Post
Third, 5200 isn't necessarily the best choice of sealants to use. 5200 has an adhesive strength greater than the underlying laminate and is very difficult to remove, again causing any future re-bedding to be more interesting than it should be. It is also not as elastic as some of the other sealant, that might be better suited to the task.
I really want the keel to stay on so I was looking for maximum adhesive strength. The real danger of a crack in the keel is corroded keel bolts and then suddenly losing the keel. If possible I would rather not have to do this again. In any case sealants can be easily cut with a knife to separate the keel and hull. But yes I know it would be very difficult to clean the surfaces afterwards. Frankly I hope this is a once only job.
Quote:
Originally Posted by sailingdog View Post
You should also inspect the keel bolts for any corrosion damage, since bolts that have sat in salt water for extended periods of time can easily be eroded away by corrosion.
Yes absolutely, I want full confidence in the keel bolts. that is the main reason I want to drop the keel.
Quote:
Originally Posted by sailingdog View Post
in your Application section, I believe you mean KEEL not RUDDER. Bonding the rudder to the hull would be a bad idea generally.
Yes you are right.
Quote:
Originally Posted by sailingdog View Post
BTW, most hull-keel joins are faired, but not glassed over. Glassing over the join can seriously complicate repairs.
If I built up the join with two inches of epoxy and matting surely this would be almost like converting to an internally glassed keel. As long as I stripped the gelcoat before this would be incredibly strong. But of course it could still devlop a crack.
Quote:
Originally Posted by sailingdog View Post
I'm sure that Maine Sail will be along with his recommendations on what sealant to use, probably SikaFlex 291 or something like that...
I look forward to hearing more on this topic as it no doubt affects many yachts.

Last edited by matt2; 12-17-2008 at 01:31 PM.
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The loads on a fin keel on a sailboat are generally such that any fairing material is going to give. They flex. They have to given the loads involved. A rigid joint, using epoxy, is going to crack rather than stretch and contract with the movement. A lot of it depends on the hull-keel join design. I don't know your boat, and I am not a naval architect.

The problem with fairing and glassing the hull-keel join is simple. If you damage the keel and need to remove it, you've vastly complicated the job. Also, that makes the hull and keel more rigid, but making it more rigid makes it far less forgiving in a hard grounding. IF it doesn't give, something else will.

BTW, if the bolts can't support the weight of the keel and the stresses it is under, even 5200 isn't going to do the job. All 5200 would do is help the keel tear off the outer layers of laminate when the keel falls off. The dynamic forces on a sailboat keel aren't such that you can rely on a sealant alone to keep the keel in place. Thinking you can do so is both stupid and foolish.
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Old 12-18-2008
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A Drawing and A Few more Questions

Quote:
Originally Posted by sailingdog View Post
The loads on a fin keel on a sailboat are generally such that any fairing material is going to give. They flex. They have to given the loads involved.
Yes I see your point. It is just that I have seen fin keels with the same design with no crack and that is what I want. Any ideas on what product would you might use for fairing in a situation that needs this flexibility?
Quote:
Originally Posted by sailingdog View Post
A rigid joint, using epoxy, is going to crack rather than stretch and contract with the movement. A lot of it depends on the hull-keel join design. I don't know your boat, and I am not a naval architect.
Yes for sure the design is a key factor I don't have any photos at present but I have attached a quick drawing done by computer (so it is a bit of a scrawl). The fin keel is the same as a Farr 38 (Cruising), which is very similar to many modern cruiser fin keels in shape and size.

It looks to me like it comes down to a choice. Taking nito account the design the choice is, either:
i) epoxy -> strong but brittle and no crack or
ii) 5200 -> strong and flexible but with a crack (and the risk of water accessing the bolts and causing corrosion eventually).

The nub of the problem as I see it is that if you have a crack along the hull/ keel join how do you know if the keel bolts are dry? It is not really practical to remove the keel every one or two years to check the bolts and rebed it.
Quote:
Originally Posted by sailingdog View Post
The problem with fairing and glassing the hull-keel join is simple. If you damage the keel and need to remove it, you've vastly complicated the job. Also, that makes the hull and keel more rigid, but making it more rigid makes it far less forgiving in a hard grounding. IF it doesn't give, something else will.
Yes good point.

To get a handle on the different outcomes of strength vs fragility I have a thought experiement, I would be interested to know if you think it roughly describes the situation.

Consider a range of forces from 0 to 500 Netwons applied to the keel on imp.act. Then there are 3 possibilities: The force is low enough that nothing happens, the force is sufficient to cause damage in one form or another, and thirdly the keel is damaged to the point where the hull fails.

o=OK
x=damage
X=catastrophic damage

Newtons 0-------100-------200-------300-------400-------500
Epoxy oooooooooooooooo xxxxxxxxxxxxxxxx XXXXXXXXX
5200 ooooooooooooooooooooo xxxxxx XXXXXXXXXXXXXX

Perhaps others will have a different opinion.

Quote:
Originally Posted by sailingdog View Post
BTW, if the bolts can't support the weight of the keel and the stresses it is under, even 5200 isn't going to do the job. All 5200 would do is help the keel tear off the outer layers of laminate when the keel falls off.
The design of the bolts is certainly sufficient for the size of the keel, in fact a bit heavier duty than used these days for similar sized and configured keels.
If the keel falls off, tearing the outer layers of the laminate is probably the least of my worries!
Quote:
Originally Posted by sailingdog View Post
The dynamic forces on a sailboat keel aren't such that you can rely on a sealant alone to keep the keel in place. Thinking you can do so is both stupid and foolish.
Um... yes it would be foolish to rely on sealant only, and so I do not intend to do that. I want to make sure the keel bolts are OK and if not I will fix them.

It would probably be stupid to do nothing.
However when it comes down to it the main reason to check the keel bolts is to make sure they have not suffered corrosion over 20 years the boat has been in the water. I really want the confidence of knowing everything is OK.

Thanks for your comments "sailingdog" I appreciate your suggestions and ideas.
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Dropping the Keel-keel2c.jpg  

Last edited by matt2; 02-04-2009 at 09:04 AM.
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Old 02-04-2009
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Keel Putty or 5200?

I have purchased "The Fiberglass Boat Repair Manual" by Allan Vaitses.

It has a section on page 132 about dropping the keel.

Actually it can be seen in a book preview by searching google for "dropping a fin keel" at www . books . google . com!

The book is very good, and the author suggests either using:

1. A bedding compound (5200) on the bolts and between the keel and stub,
OR
2. Waxing the bolts and one of the surfaces (top of keel or bottom of stub) for easy removal and then using a "keel putty" of filled resin.

A "keel putty" is I think an epoxy putty like Marine-Tex. I am not sure but I guess this is probably epoxy with microballoons mixed to something like peanut butter like consistency. Anyone know if this is correct?

The author does not mention anything about fairing in either scenario. Nor does the author make any suggestions on exactly how to drop the keel.

Anyway making some progress and it looks like it comes down to a choice.
5200 or keel putty.

I saw one keel crack fixed and the shipwright there used a brown resin paste.
Which I guess is the keel putty. In that case he did not apply any wax or release agent though. Seems that if a release agent is used without any sealant at all then you would have a problem should the hairline crack reappear? Any comments.

Unfortunately, although the Goudgen Brothers book is very good, there is nothing I could see on dropping fin keels.

Still waiting on a few more books on the subject. Any further comments would be greatly appreciated.

Last edited by matt2; 02-04-2009 at 09:01 AM.
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One thing you might consider if you are worried about crevice corrosion is replacing the keel bolts with something other than stainless (assuming they are stainless now). The feasibility of this would depend on how the existing bolts are attached to the keel -- are they "j" bolts that were put in the keel when it was cast (i.e., bent into a j shape) or are there pockets in the keel and the bolts are basically a rod with threads and nuts at each end? If the latter, it is possible to replace them. This is actually what I am doing on my boat right now (the keel is coming off this week). We are going to use silicon bronze for replacement bolts, which avoids the crevice corrosion issue. More expensive than stainless, but more durable for this application. There are other options than silicon bronze as well.
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I am no expert but I think if the keel bolts allow the keel to flex at the joint there is no putty, epoxy, or adhesive that will prevent a crack from appearing. If the keel bolts are correctly designed and torqued almost any conventional method of sealing the joint will work.
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This is really good with plenty of pictures , I can't recall who posted it BUT i found it worth reading
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There are a few ways to re-bed and none of them, for me, would involve only epoxy. Fin keels move and flex regardless of how you attach them. Epoxy it on and it will still move or flex some and the epoxy has nearly ZERO elongation before break sio it will fail.

The best method I've seen is to mix an epoxy butter and then heavily wax the lead keel & bolts, or better yet grease the bolts. Drop the boat onto the keel and epoxy butter, let it cure lift boat off. Now you have a nicely matched hull to keel joint. You can also do it in reverse but I prefer the bond of epoxy to fiberglass as opposed to epoxy to lead for the epoxy butter mixture though eitehr is probably fine.

Next you take a Dremel tool and cut a shallow v-groove into the top of the lead face of the keel that meets the hull. A laminate trimmer and edge guide with v-bit works better if the keel is wide enough for it to fit. Go all the way around the keel about 3/8 to 1/2" in from the outer edge until you complete a circle and the v-groove joins its self. Now apply a marine sealant, I like Sikaflex but 5200 is also good (but very permanent and it may rip the epoxy butter off on the next round) as is 4200, and drop the boat back down. The v-groove makes a nice thick gasket that can absorb lots more flexing than no thickness or minimal thickness. A 1/8" thick bead of 5200 will stretch and move a LOT more than 1/64th of an inch of sealant before a failure.

Most all builders DO NOT take the time to make a "gasket groove" or to "butter match" the hull to the shape of the keel. It involves a LOT more time than builders are willing to exert or spend time/$$ on.

Please for your own sake do not solely use epoxy. You need some allowable movement as the forces on a fin keel are tremendous and I've yet to see one that did not move some. Any movement with epoxy will mean failure and adding stuff to to to make it more flexible is not enough. Just because a fairing compound has cracked due to movement does not mean the marine sealant between the hull and keel has..

Here's a link to a good description though they did not cut a sealant/gasket groove..

Keel re-bed (LINK)
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