Theoretical Keel Question (Encapsulate a Bolt-on)

[minaret]

Originally Posted by GrahamHO

Not my idea but a standard boatbuilding practice in AKL. NZ; A normal hole saw is usually extended with a tube welded in I think in a lathe. No pilot drill is necessary as the bolt guides it.
A sledge hammer on the outside finishes it off with the yacht suspended a couple of inches clear in a travelhoist.

What about all the contact area between the top of the keel and the keel stub or inset? We did just what you described, and still had to use severe measures to get the keel to drop. This included grinding through the exterior skin into the core to access the joint inside the inset, all the way around the keel, followed by driving steel wedges into the joint all the way around. Had to reglass the entire inset afterward. Should have been a simple job, ended up costing the owner a fortune. The designers were in agreement that a flexible bond is superior, to prevent the chance of the joint cracking in a hard grounding.

[GrahamHO]

Originally Posted by TrentePieds

Indeed. Nothing wrong with that at all, but use your noggin when you do it.

A friend of mine had a boat in slings off a dragline converted to a crane. The nuts had been removed from the bolts. The bottom of the keel was 2 inches off the deck. He hit the keel exteriorly on the side with an almighty wallop of a sledge. The bolts did what he meant them to do, but the weight coming off the crane permitted the jib boom to rise enuff to let the tops of the bolts clear the bottom of the boat. The keel toppled to HIS side. It didn't do his legs any good at all!

TrentePieds

Sounds like that was because a crane was used. I've only used a travel hoist capable of lifting a much larger vessel. I was just assisting a couple of boatbuilders and the travel hoist driver who were experienced in that part of the operation. The travel hoist slings didn't spring at all. I hope your friend is OK.

[GrahamHO]

Originally Posted by GuidoY

Just thinking of the best of both worlds, (fully lead + encapsulated & i like the fin keel) but clearly there are pros & cons to each.

The heavy epoxy approach seems good, and similar to the method used in the link posted on p1. Is the epoxy also applied to the threads where they meet the nuts, freezing them in place?

What about the Polbream? Quite a bit of cheating death there. Looks like there was actually no keel stub to speak of, just some kind of cross brace & some bolts. Seems a bit underbuilt for such a high end boat.

Maybe a sectional break away type could be invented for just such an emergency. Lose part but not all and keep the boat upright.

I used the strongest red Loctite on the nuts. I can't remember it's number. I've still got it but it's in Auckland and I'm in Chicago today. I was told Loctite was not necessary but I'm a pessimist. By the way my new keel (and the attachment method) was designed by professional yacht designer with an international reputation.
I'm fairly sure we applied parting compound to the underside of the hull before we fitted the original keel using the same method 30 years ago. There was no damage to the hull when that keel was removed. I think we used parting compound with the new keel. I could confirm that in 2,1/2 weeks when I'm home again if anyone is still interested. It is the epoxy bond between the threads of the keel bolts and the hull that keeps the keel in place supposedly not needing nuts; but again I'm a pessimist and fitted nuts machined from 2205 SS featuring an integral flange like a built in washer on their bottoms.

[GrahamHO]

Originally Posted by minaret

What about all the contact area between the top of the keel and the keel stub or inset? We did just what you described, and still had to use severe measures to get the keel to drop. This included grinding through the exterior skin into the core to access the joint inside the inset, all the way around the keel, followed by driving steel wedges into the joint all the way around. Had to reglass the entire inset afterward. Should have been a simple job, ended up costing the owner a fortune. The designers were in agreement that a flexible bond is superior, to prevent the chance of the joint cracking in a hard grounding.

I'm sure either method carried out correctly is fine. To me flexible suggests movement and movement plus stress means strain. If my keel, new 5 years ago lasts the 30 years the original keel did I'll be 101. The old keel was only changed for a better design. It had no structural problems.

[TrentePieds]

Originally Posted by GrahamHO

Sounds like that was because a crane was used. I've only used a travel hoist capable of lifting a much larger vessel. I was just assisting a couple of boatbuilders and the travel hoist driver who were experienced in that part of the operation. The travel hoist slings didn't spring at all. I hope your friend is OK.

Thanks for the good wishes :-)

The incident happened so long ago that if travel hoists even existed, they hadn't reached these shores yet. All manner of equipment was used then which would be outlawed by "WorkSafe" (Workers Compensation Board) today.

To add insult to injury, my friend was an engineer (P.Eng.) and actually a good one, if quite young. I cannot imagine how he could have failed to foresee, and account for, the springiness in the setup.

He went on to build a successful yacht maintenance business. Talk about making lemonade from the lemons life hands you :-)

TrentePieds

[leftbrainstuff]

Originally Posted by GuidoY

If one were so inclined, and had the resources, would it be possible to encapsulate a bolt-on keel? Would it be advisable?

That is, grind back glass on and above the stub, graft new glass in, encapsulate keel, fill, fair, gel, etc.

I like having solid lead, and bolt-on is fine, but just wondering in case I want to upgrade the strength or make it more suitable for longer passages.

This seems like a good compromise/approach, but I'm not in the market right now.

Assuming you want to encapsulate such that the original keel bolts become redundant. I'd class that as major structural work.

Much simpler to buy what you want. In answer to your question. Anything is doable. The question is the benefit worth the effort? Do you want to sail or work on a boat?

When we were shortlising we excluded anything with a bolt on keel. We watched and waited until we found our first choice. A Liberty 458.

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[bwells79]

It is my understanding that Stainless Steel should not be used where they are not exposed to air. I am in the process of rebuilding a 1965 Century Inboard and the recommended fastener material is Silicon Bronze because all the fasteners are either below the waterline or encapsulated, either with filler or bungs. I don't pretend to understand the chemistry, but the lack of oxygen causes the SS to loose its corrosion resistance.

If you do choose to encapsulate the bolts, make sure you don't outsmart yourself.

[TrentePieds]

Somewhere I have from years ago a surveyor's treatise on "crevice corrosion in stainless steel" occasioned by a mast going overboard as a consequence of a forestay bottle screw which had cracked where the threaded fork shank entered the bottle.

SS is used only because it is so much cheaper than bronze and gun metal and is perfectly serviceable as long as air can get at it.

I am not up on the chemistry, either, but perhaps someone here is.

TrentePieds