eyebolts embedded in epoxy

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eyebolts embedded in epoxy

Postby DanaDCole on Tue Dec 02, 2014 11:04 am

Reading ahead to the rudder installation, eyebolts and a rod are used to good effect instead of gudgeons and pintle, but I have discovered a potential problem. The method for securing the eyebolts in the keel and in the rudder is to drill a hole slightly larger than 1/4" and slightly deeper than 3" and fill it with thickened epoxy, then drill a hole "slightly smaller than the threads" in the epoxy and force-thread the eyebolt in. As John states, the eyebolts are 3" long, and when force-threaded into thickened epoxy will be mechanically quite strong. This is true, but the problem I want to point out is that the last half of the shaft is coated with epoxy before the eyebolt is threaded the rest of the way in, essentially embedding the stainless steel shaft in epoxy.

Stainless steel, as you know, is the opposite of most metals in one respect: It corrodes due to lack of oxygen and should never be embedded in epoxy.

I would like to suggest two possible solutions for the engineers among us to mull over and weigh in on:

First drill 3/8" diameter holes in the keel and rudder, about 3 1/2" deep. Fill the holes with thickened epoxy and allow it to cure. Drill 13/16" diameter holes in the cured epoxy, 3 1/4" deep. Tap 1/4-20 threads in the epoxy. I'm assuming the eyebolt threads are 1/4-20--they might be 1/4-28, haven't checked--either way, tap the correct thread. The eyebolts can then be threaded into the tapped holes and should be mechanically strong, given the three-inch long shafts. There is no worry about the eyebolts loosening because the "pintle" will prevent them from turning. In fact, I would think they should not be threaded in all that tightly, just snugged, then backed off until they are horizontal.

An alternative might be to force-thread the eyebolts into the epoxy, as John suggests, but leave out the last step of adding fresh epoxy to the last half of the shafts. This might be stronger than tapping threads into the epoxy first, after all epoxy is not metal.

One caveat: It is very hard to drill the smaller hole into the epoxy and be sure that your drill has not hit wood somewhere along the 3 1/4" length. Sealing the last half of the eyebolt in epoxy makes this a non-issue (but it also makes a broken eyebolt much more difficult to replace). Perhaps the beginning holes should be 1/2" in diameter or even larger to make hitting wood less likely?

I look forward to reading what others who are more knowledgeable think of my ideas, or from those who might have better suggestions.
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Re: eyebolts embedded in epoxy

Postby craig on Tue Dec 02, 2014 2:57 pm

I actually didn't know that about stainless steel and oxygen deprivation -- interesting! My interpretation of the manual at that point of construction are very different. I understood them to mean that you do NOT pre-drill and fill with epoxy. Rather, you drill small, fill with unthickened epoxy, screw the eye-bolt in halfway, re-fill with more unthickened epoxy, and screw the rest of the way in. The combination of epoxy glue and thread grip on wood will anchor the eyebolt securely. Remember, the bottom eye-bolt is 3 inches or something long, and so will protrude from the wood backer in the keel into the hollow keel space back there. If the entire thing isn't waterproof, you'll slowly leak water into that compartment and cause all sorts of problems since it can't drain out. So I believe John Harris specifically wanted the bolt soaked in epoxy. Maybe the corrosion is very slow and won't damage the integrity of the bolt? I certainly hope so, because I've already embedded several stainless parts on the mast and rudder in epoxy!
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Re: eyebolts embedded in epoxy

Postby Shudoman on Tue Dec 02, 2014 3:45 pm

Doh! Me too.
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Re: eyebolts embedded in epoxy

Postby DanaDCole on Tue Dec 02, 2014 9:45 pm

Good point Craig! It had not dawned on me that the bolt would protrude into the hollow, hence it has to be sealed very well. After re-reading I'm starting to agree with your interpretation. I just assumed we were not given a lot of hand-holding here because we have done this sort of thing before several times by the point we get around to installing the rudder.

At any rate, you are correct either way, the bolts will protrude into the hollow spaces both in the keel and in the rudder and the last thing you want is water infiltration into either one. So, I think the prudent thing is to stick with the method in the manual. As John points out, he has been doing this sort of thing for years and never had any problems so far. Maybe the corrosion that does occur on the bolts is not that big a deal.

In the meantime, though, I'm going to be looking into bronze gudgeons and pintles. As for people with the stainless steel eyebolts already installed, maybe they will last for ever--I surely hope so. But if they do fail all is not lost, the remedy would be to cut them off, seal up the holes with epoxy, and install gudgeons and pintles in their place.
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Re: eyebolts embedded in epoxy

Postby Bflat on Tue Dec 02, 2014 10:58 pm

I'm having trouble finding evidence of problems or warnings against sealing stainless steel in epoxy. Some sites talk generally of possible crevice corrosion to do with a lack of oxygen, but that seems to occur only if other variables are involved to encourage corrosion. "Sealing" in and of itself doesn't seem to be a problem. But, I may be wrong.

One could use bronze eyebolts instead of stainless. Bronze wouldn't be as strong as steel, of course.

One thing I wish I had done when building my rudder is to add the appropriate blocking to support a pintle if I ever decided to go that route.
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Re: eyebolts embedded in epoxy

Postby DanaDCole on Tue Dec 02, 2014 11:46 pm

I could not find the article I read that specifically states to not embed stainless steel in epoxy--if I do I'll post it. I do know that in the presence of oxygen a chromium oxide layer is formed, which is what protects the stainless steel from corrosion. There are many examples of stainless steel corroding badly when it is mounted on the keel of a boat that never leaves the water.

As you point out, though, the corrosion is not usually a huge problem and there are probably no worries unless the boat is left in the water all the time. I think most of us are trailering, so don't have to worry about that.

Your idea about bronze is pretty good except that you then run into the problem of electrolysis with dissimilar metals. I'd have to look it up, but I think bronze and stainless steel is one of the few combinations you don't have to worry about though (anodic index difference less than 0.3). To be on the safe side, especially if the boat stays in the water, might be all bronze eyebolts and rod, etc. True, they are not as strong as stainless steel, but the rudder is comparatively very light.

In the meantime, I am still looking for suitable gudgeons and pintles. I also like that idea because if the rudder hits something pretty hard under water it will simply be pushed out of the gudgeons instead of possibly tearing out one of the eyebolts. I would also install a small hold-down so the rudder is not flying out all the time--if something heavy hits it the only damage would be the small hold-down screw being ripped out.
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Re: eyebolts embedded in epoxy

Postby DanaDCole on Wed Dec 03, 2014 7:25 am

I just took a more careful look at the manual. It appears to me that the lower hole in the keel is low enough that the hole is drilled into the vertical and then horizontal blocking at the bottom of the keel. At the top the hole is drilled through the transom. If I am correct, then you would not be drilling into the hollow area of the keel, nor of the rudder. At the bottom of the rudder, the hole is also drilled into vertical, then horizontal blocking. At the top of the rudder the hole is drilled into the triangular blocking. So again, if I am correct, none of the holes are drilled into hollow areas of either the rudder or keel.

Also, regarding Bflat's comment about pintles, this means that the blocking needed for pintle support is present in the rudder, top and bottom, though it's possible the bottom pintle might have to be shortened a bit.

For those who will be leaving their boats in the water, it seems to me that gudgeon and pintle would be necessary. They would need to be bronze on the bottom set that is always submerged, or else plan on replacing them from time to time.

I'll be glad when John Harris or someone else with more experience in the real world reads and weighs in on all this. My comments are based mostly on "book larnin'."
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Re: eyebolts embedded in epoxy

Postby John C. Harris on Wed Dec 03, 2014 10:18 am

Boatbuilders have been bedding stainless steel in epoxy as long as they've been building with epoxy. The Gougeon Brothers boatbuilding book, from 30+ years ago, is the original source of "hardware bonding" techniques. I can't see how you could use stainless steel fasteners in boatbuilding without..."depriving" the stainless of oxygen one way or the other. I mean, if you thread a bolt or screw into wood, there ain't no oxygen in there...

I've installed 2000-pound fin keels on big boats with stainless bolts cast into wet epoxy. It's the usual practice in new boat construction.

Anecdotally, PocketShip #1's rudder eyebolts are the originals and show no trace of corrosion or oxidization, nor any hint of failure in spite of hard usage. Just had them out a few days ago, as we're refreshing PocketShip's transom.
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Re: eyebolts embedded in epoxy

Postby craig on Wed Dec 03, 2014 11:46 am

Dana: I think you're right, good point about going into the keel blocking with the lower eyebolt.

John: Thanks for the info. That's good to know. Of course no hardware lasts "forever" and obviously I'll have to replace the parts anyway.

For what it's worth, I decided to copy Dave's rudder hardware: pintles and gudgeons ordered from Duckworks. For the top I used RL-390 pintles and gudgeons, and for the bottom of the rudder I used the Weekender Gudgeon and the RL-390 pintle (You need the weekender gudgeon here because the stem of the keel is so narrow). No pictures because I just took everything off to varnish the transom, but it looks beautiful. I found that the difference in price is fairly trivial compared to stainless eyebolts, cotter pins, and rod from the local home center.

Bonus: I didn't know this, but apparently the long pintle is for the bottom of the rudder, and the short for the top. That way you can insert the long pintle first and then swing the short pintle into alignment -- makes putting the rudder on easier, especially in murky water. Otherwise you need to align top and bottom simultaneously.
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Re: eyebolts embedded in epoxy

Postby DanaDCole on Wed Dec 03, 2014 3:52 pm

Glad John Harris chimed in. Remember what I said about "real world" vs. "book larnin'?" He's been doing this for many years with no problems. Maybe the stainless will fail after enough years, but everything fails eventually.

For the record, I remembered my source for not embedding stainless steel explicitly in epoxy. It is in the System Three "Epoxy Book," page 15, i.e., "Don't pot stainless steel bolts in any epoxy resin if the application will be around water. . . . Stainless steel fastener failure occurs where the bolt emerges from the epoxy resin." So I guess it works OK with MAS Epoxies, but not System Three! :-) :-) (I still think it might be a bad idea for boats that stay in the water, especially salt water.)

Anyway, I will probably use the gudgeon and pintle method. Easier to install, easier to replace if they fail, and easier to remove and replace the rudder (but be sure to use a holddown). And, it's looking like it will be fairly inexpensive from Duckworks.
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