Replacing Keel Bolts, One at a Time

[Charlie]

OC:

I am with Minaret on this one. I would tend to leave the bolts in place and double up some new bolts. Get one of these -- http://www.rockler.com/product.cfm?p...FYl7QgodwkQAwg a portable drill guide. Drill holes straight down and then either thread or epoxy new bolts in place in between existing bolts. I think that this would be safer and easier. Lag bolts would be easiest but you could also use thru bolts.

[OrangeCrush]

Really?

I like the simplicity of that, but I was thinking that replacing them outright seemed like a more complete fix.

Would I just drill right through the thick fiberglass backing plate and into the keel next to each bolt? Tapping suitable threads in the holes seems like it could be challenging, and epoxy alone doesn't seem like it would be enough. What about heat buildup against the hull?

I'm seeing some people drill in sideways from the outside of the keel and insert a threaded rod to accept the new bolt. Why wouldn't this be necessary in my case? It seems like since my bolts are only 3 1/2 inches long and removable that it would easier to just change them, no?

[minaret]

3 1/2" keel bolts, LOL! Easy peasy, just do it. One at a time, no problem. I'm used to keel bolts 5' long...

[Charlie]

Ok here is my thought. Minaret has way more experience then I do. Epoxy should be strong enough to hold the bolts. I have done this with holddowns on buildings for earthquakes. Tapping thru cast iron I don't think it will be easy. But 8 bolts are going to be stronger then 4 as long as there is meat on the keel. I guess that your first try would be to get one of the bolts out. If it works then do the rest. If not you can alway add more bolts.

[denverd0n]

I still don't get why you would do this. The "right" way to replace keel bolts is to haul the boat and do them all at once. So, you can't do that now, and you don't have any reason to believe that there is anything wrong. Still, to sleep better at night you're going to replace them the "wrong" way.

In order to avoid a problem that you might, maybe, possibly, someday have, you are going to risk creating real and immediate problems with the keel alignment and tensioning of the bolts. Honestly, no offense intended, but that makes no sense to me at all.

[minaret]

Originally Posted by Charlie

Ok here is my thought. Minaret has way more experience then I do. Epoxy should be strong enough to hold the bolts. I have done this with holddowns on buildings for earthquakes. Tapping thru cast iron I don't think it will be easy. But 8 bolts are going to be stronger then 4 as long as there is meat on the keel. I guess that your first try would be to get one of the bolts out. If it works then do the rest. If not you can alway add more bolts.

I would never epoxy in a keel bolt. A little cutting oil and a nice new tap and bottoming tap will do the job nicely. Otherwise you are relying on an epoxy bond to cast iron to hold some massive dynamic loading. Guaranteed to fail. Tapping in lead ballast is so easy it's silly, and I always feel like more bury is needed than the official numbers because its so soft. Cast iron is more challenging, but still totally doable. I'd be more concerned about drilling than tapping.

[minaret]

Originally Posted by denverd0n

I still don't get why you would do this. The "right" way to replace keel bolts is to haul the boat and do them all at once. So, you can't do that now, and you don't have any reason to believe that there is anything wrong. Still, to sleep better at night you're going to replace them the "wrong" way.

In order to avoid a problem that you might, maybe, possibly, someday have, you are going to risk creating real and immediate problems with the keel alignment and tensioning of the bolts. Honestly, no offense intended, but that makes no sense to me at all.

Much more likely to have alignment problems dropping the keel than by this method. We do it in the yard all the time for boats which are too small for non invasive survey methods to be cost effective. Often it's cheaper just to install new bolts. Often the owner doesn't want to spend the money to drop the keel and "do it right". It does cost a lot more. A quick replacement one at a time, or sistering in new bolts is a quick fix which works perfectly well for less money. Usually we glass the keel stub/ballast keel seam when we do this, since we haven't been able to rebed the ballast keel. This ensures the new bolts stay dry.

[Teknav]

Before replacing any keel bolts, make sure that you have access to all of them and that you can apply the right amount of torque to tighten them. Some of these bolts are located in very tight corners that it is difficult to re-attach/replace them, let alone torque them correctly. Mauritz

[OrangeCrush]

You make a good point, Denverdon; perhaps I'm trying to have my cake and eat it too. But here is my thinking.


1) I don't have any specific reason to think they are bad, but they are 10 years overdue for an inspection (according to what I'm reading). They are showing significant signs of corrosion and they suffered a hard aground a few years ago. I take my boat 80-100 miles offshore when I sail across the Gulf of Maine and the water there is mighty cold. Losing the keel could definitely turn deadly in a hurry.


2) My instincts tell me that I am going to have more alignment issues dropping the keel than just replacing the bolts, as minaret says. Unless I'm missing something, I really don't see what would be accomplished by dropping the keel besides keeping the mating surface smoother and the bolts dry for longer. If the bolts are new, the keel will not break off for quite a while, even if they do not stay bone dry (although I think they very well might).


3) I could glass over the keel/hull joint, but the 5200 I put on there 4 years ago (right after the hard aground broke the old caulk) is still flawless and dry. Just glassing the sides of the bolt holes seems like it would keep the new bolts dry to me, since there is no sign of wiggle on the mating surface. If there is old water trapped in between the keel stub and keel, then it will corrode the top of the keel a bit, but I don't think that will be too critical. I could also scrape out the old caulk and rinse out the gap with fresh water, dry it thoroughly with a heat lamp, then recaulk. Any thoughts on this step, minaret?


3) If I find that there is not enough 'meat' on the iron flange of the keel to accept the new bolt heads securely, I will probably have to drill 'sister' lag bolts as minaret originally suggested. I do like the redundancy of sistering the bolts, but I'm wondering how strong a thread tapped into cast iron can be, especially after a couple of years of corrosion. This also sounds like a long and hard process, and may result in cooking the fiberglass stub if the holes get too hot. I like this technique because it would not be opening up any new holes for water to leak in, but since a couple of the bolts are weeping rusty water already, they old bolts would have to be dug out and glassed over anyway.


I have a short window to get this season's work done: only 3 to 4 weekends worth of work depending on the weather. If I take longer, I will need the yard to move me, since I am located in an 'early in' spot and I'm blocking other boats. They will probably want to charge me for this. If I had to drop the keel and rebed, I am anticipating losing some or all of the sailing season and spending a lot more money. If I change the bolts, I can have peace of mind for at least a few years, and I won't be making the job any harder when I eventually drop the keel and do it 'right.'

Teknav, there is one bolt that I will have to do some cutting to get proper access, but I have a dremel tool that can handle this and it is not a structutally important piece.

Jack

[OrangeCrush]

Also, any insight on the choice between Grade 5 or Grade 8 steel nuts to go with the bolts I linked to?

Thanks!

[OrangeCrush]

Hey all,

I'm happy to report that I successfully removed four of the bolts. They came out very easily and things are looking great overall. With one exception, the nuts actually came off the bolts, and the bolts were hammered out easily. The bolt holes look clean and dry (with one exception) and the recesses in the cast iron keel are showing no corrosion at all, leaving only smooth and clean surfaces to attach the new bolts.

The only issue I found at all was a mistake that it seems the factory made when they originally drilled the holes in the hull. One of the holes was drilled in the wrong spot, moved over slightly and drilled again. They never filled it in, which left a gap under part of the washer. This is where the rust streak I observed was coming from, since water was able to seep into this recess, probably from the bilge, then make its way down and out. I will fill this irregularity with epoxy and high density filler, using a greased dowel to create a smooth hole for the new bolt.

Since the only bad bolt was the one I suspected from the beginning, I am leaving the remaining four bolts in place. I now have a visual inspection on half of the total number of bolts, and I'm confident that the rest are clean and strong.

Everything seems straightforward to me from here. My biggest problem, now, is finding the right replacement bolts for the four I took out. I can't go with stainless, I'm told, since it will be completely deprived of oxygen and because it won't react well with the cast iron. The black oxide alloy bolt I linked to on McMaster really doesn't seem right to me, since it's not a high strength steel and it offers absolutely no rust protection. (I bought one to see, and attached a picture of this bolt next to one of the originals, which looks galvanized). Nobody seems to make this bolt in a galvanized version anymore. The best I can find is a Grade-8 Steel with Zinc plating. Does this sound ok?

Anyway, I wanted to give everyone an update since you were all so helpful. If you have any insights on the metal type, please let me know.

Best,

Jack

[MonkeyBusiness]

Galvanized means zinc plated. The grade 8 bolts will probably work just fine for you.

[Andrew Troup]

Originally Posted by MonkeyBusiness

Galvanized means zinc plated. The grade 8 bolts will probably work just fine for you.

I'm sorry, but while you are correct in terms of linguistic origins, that's not correct in the way the terms are used in the steel protection industry, and this means the terms which are used when fasteners are bought and sold.


Zinc plating is an electrochemical process, suspending an item in a bath of a solution of a zinc salt in water, and applying a current through the two, to transfer a very thin coating of metallic zinc.

Unless qualified by some additional words, 'galvanizing' is taken to refer to hot-dip galvanising.

The thickness achieved with plating is orders of magnitude less than the heavy build offered by galvanising, which requires dipping the item in a bath of pure molten zinc.

In the latter case the coating is so thick that the threads must be machined significantly undersized, if the fastener is to be galvanised.

Given that zinc gets consumed in offering protection to the underlying steel, the zinc thickness is a crucially important distinction. Zinc plated bolts are not suitable for marine environments except in special circumstances, say on an oily motor

There is no way on earth a zinc plated bolt should be used as a keel bolt, except possibly for short term use in fresh water, whereas good quality galvanised bolts will generally last for many years before needing replacement.