Keelbolt Arrangement

[nofacey]

Dropping the keel is not going to tell you anything!....you need to inspect the internals of the welded structure, and that is all below the hull. Good news is you don’t need the time consuming step of dropping the keel. Just need to access welds hidden by whatever was used to close off the sides of the welded structure.

Question is how did they finish/fair the sides of the extension?
- Welded steel - drill a couple small bore holes, insert video probe & visually inspect.
- cast lead - not likely - heat would damage the hull joint above, so you’d have to gouge it out, very hard to replace in kind.
- bog/fairing compound- that’d be my guess. Dig it out using something like a router/vibrating saw/chisels till you can see some weld. Dirty job, but not overly difficult.

[darylat8750]

Originally Posted by boatpoker

If I'm understanding what I'm seeing .... One would have to cut through the side of the stub to access those lower bolts.

Also one one woould have to cut off the sides of the stub to inspect the welds for corrosion.

No thanks.

This.

[Cheechako]

Maybe the metal is a tool for manufacture, not part of the actual keel?

[Capdave360]

Originally Posted by Muaddib1116

Hi guys, I am under contract to purchase a 52' sailboat, and in the course of the initial on-land survey I got these pictures of the keel/keelbolt arrangement that I think were taken during the initial construction in 1997. I've never seen a setup like this, and am hoping to get some opinions of the pros and cons of it. Given where the internal access to the keelbolts is, it seems like they are about a foot down the keel in a keel stub.

Studying the pictures, and reading the new information OP added along the way - it's pretty clear this keel arrangement was a modification/retrofit to the original design, presumably because the performance of the original design wasn't acceptable.

That alone would be enough to make me run away. Who knows if the design issues were really fixed? Who knows what other design issue compromises were left unaddressed? There are reasons why boats designed by NA's with large bodies of work actually at sea and built by yards with large fleets actually with sea time generally command higher prices and tend to hold value.

The concern about the integrity of the modification can be satisfied with money, probably not that much, but the question is why?? Are you that much in love with this one boat?

I'd consult a lawyer ASAP and bail.

My $0.02

[jeepers]

If the Surveyor had access to this information doing the survey. He has accepted the responsibility. Confirm existence of his professional Insurance. Then likely so did the owner know of it. Whether they understood the ramnifications or not is irrelevant. Due diligence at that moment was on them. Your due diligence has uncovered this "custom" repair to the assumed original design, that you were accepting. It was after, that you received the photos.... Did the original Builder -Yard encapsulate this attachment in lead before installing the keel? Is the keel area both on the keel and hull essentially as original designed plans show. There maybe further deviations from the original as designed plans to accommodate this change. (Those changes might include a recessed area/pocket providing superior shear protection than originally designed.) Are there any as built plans from the yard? Your recourse after the fact should anything arise after delivery could involve the Owner as well as Surveyor & the original Builder/Boatyard if they made "unauthorized" changes to the as designed plans without changing the boats model name/number.

[Ken Fry]

Originally Posted by Muaddib1116

I've never seen a setup like this, and am hoping to get some opinions of the pros and cons of it.

All cons, no pros.

This is really awful, in my opinion.

The structure is unsound, as compared to the usual arrangement, in which, when the boat is heeled over and pounding through waves, the bolts to windward are in near perfect (very high) tension, with their bottom ends cast deep into the lead. For movement to occur, the bolts must stretch beyond their preload from torquing them. Stretch, they will, but by only a couple thousandths of an inch -- an amount easily accomodated by the sealing medium between the keel and hull.

In this structure, however, the steel plates through which the upper bolts pass will flex substantially under the same condition. The span, from cross-piece to cross-piece, is too long to prevent such flexing. In other words, that steel plate will act like a diaphragm.* This flaw in the structure could be partly fixed by welding a band of steel plate around the perimeter of that steel structure to restrain the diaphragm. That would, of course, cause other problems, such as making the lower keel bolts nearly impossible to inspect (and it would be impossible to retorque the lower bolts, of course... just as it is now.)

Even if the entire space between the top and bottom plates was full of lead, (incredibly unlikely -- because then someone would have wisely said, "Let's just cast a new keel and use this one on another boat better designed for it") then the problem still occurs: the bond, in tension between the steel and the lead is insufficient under tension, so the steel will still flex away from the rest of the keel.

When I first saw this, I thought, "I bet they tried to gain a little draft and maybe even move the keel back a little bit, for either mass balance or lateral force balance (to deal with unacceptable weather helm, for instance.) However, what a crude way to go about that! Funny that the boat builder claimed this same rationale -- which I find hard to swallow. Even for a prototype never to be released to the public, this would be a stretch. Even a prototype should have a proper keel mounting arrangement.

4 inches of additional draft in a 52 foot boat (with perhaps 16 feet of beam) is a tiny amount. I seriously doubt that any cruising sailor could tell the difference. (I've sailed with reasonably competent cruising sailors who cannot tell the difference -- in sailing dynamics -- between a shoal draft and deep draft Catalina 30, where the difference,in percentage terms, is huge)

So I wonder if the reason has to do with the boat not being able to meet self righting (limit of positive stability) requirements. The Offshore Racing Rules dictate minimums, and perhaps the boat could not meet these minimums. Or perhaps it could not meet the European standards... or insurance standards... but 4" in a 52 foot boat is very, very, suspicious, and would have to result from a calculation, rather than sea trials. Can you imagine a designer coming back from a sea trial and saying "I think we need 4" more draft... then she'll sail perfectly. And let's add draft by some incredibly complicated, badly designed, hard to service means." )

If the boat has compelling appeal in other respects, then I would want to see the original limits of positive stability calculations. And I would want to see a proper keel, without double the usual number of failure points. Kudos to your surveyor, if he is the one who uncovered this.

Your concerns about crevice corrosion are right on the mark. Whoever said it is not an issue is wrong. Whatever is filling the space in the structure between the upper bolts and lower bolts will cause crevices, and those crevices will fill with sea water, which will concentrate, and... there you have it.

In Finland, this sort of work is called "Russian Style" (which I say with apologies to my Russian friends) "Slap dash". "Good enough for gummint work."

Any keel boat must have a well-designed well-installed keel. Lose a keel, and you are in a world of hurt. It is easy to do it right, and this is not done right. Just the idea of having twice the number of keel boats to fail and check is disqualifying -- especially when half of them are inaccessible.

Consider the implausibility of it all: Someone wants 4" more draft on a 52 foot boat?? If that were true, then you could conclude that the original design was really poor, and they were doing anything to make it sail better.
Even in a 30 foot boat, the difference between deep and shoal draft is apt to be a foot or more. So it is not performance, per se (to stiffen up the boat a little). It is a bad work around for fundamental limit of stability issues.

What else in the boat's construction was done in a similar fashion? I would suspect a lot. Arguably, the keel joint is the most important one on a boat.

I would run away from this boat.



* For the doubters among you. Grab a shroud with 2000# tension on it. Push or pull on it, (perpendicular to its length) with just 20 pounds of force. It moves, visibly.

[vic008]

I would go with Ken Fry.
Are assumptions being made about the deposit. Explaining your concerns to the vender may well result in an amicable outcome. Until you are certain of their atitude, this hopefully could be pointless, and you would walk away, with your money back.

[Hardhead]

I probably missed it - but does anyone know the weight of the bolt-on keel?

In my mind - assuming I was paying a substantial amount - for this large of a boat - I wouldn't want any nagging worries offshore, for the rest of my life, as to whether the keel is corroded, and going to drop off or not... Then, after any inadvertent grounding - the worries probably only increase. Seems like a kind of hell to me (that I'm buying onto) - when I'm actually trying to go sailing to get away from worries. That's just my uneducated opinion though.

[Ken Fry]

Originally Posted by donradcliffe

Speaking to engineer to engineer, the fact that there is NO telltale signs of corrosion discoloration in the stub keel, and the fact that it is MUCH more likely that any leakage of salt water into the fabrication below the stub keel would have come from water sitting inside the stub than through the fiberglass sheathing of the stub, I would say that the welds are likely to last your lifetime.

If you want further assurance, than a test by boring into any one of the cavities below the stub should either eliminate corrosion concerns or dictate that you test all the cavities.

It is NOT a fact that "there is NO telltale signs of corrosion discoloration." Only the surveyor could say that, but he would be a fool to do so. The sump (the area inside the fiberglass stub keel) would have been thoroughly cleaned as part of the pre-sale cleanup. One could only assess corrosion, and especially crevice corrosion, by removing the keel nuts at this point, and examining the visible part of the bolts for corrosion.

You write: "the fact that it is MUCH more likely that any leakage of salt water into the fabrication below the stub keel would have come from water sitting inside the stub than through the fiberglass sheathing of the stub..."

Apparently, you do not understand the construction here. The fiberglass sheathing of the stub does not protect the weldment from water intrusion. The weldment is below the stub keel, and constantly submerged. The joint between the weldment and the stub would be sealed by any of the usual goops, any of which can leak. Then there is the fairing, that can also leak. No one has said what material was used to fair in the weldment. It could be hygrospopic body putty , hygroscopic polyester resin filler, foam, etc. It would be remarkable to find that the area around the original keel bolts is dry. It is the perfect environment for crevice corrosion. When the original keel bolts fail, they will likely do so suddenly, with the failure of one causing additional load on the next, etc. Think about how easily cloth tears if you start at an edge.

You write:
"I would say that the welds are likely to last your lifetime." Based only upon a fuzzy picture of a boat you have never seen? Wow.

You write:
"If you want further assurance, than a test by boring into any one of the cavities below the stub should either eliminate corrosion concerns or dictate that you test all the cavities."

Wrong. A good survey MUST check every keel bolt, not just a sample of one.
That means, in this case, that all the fairing material must be removed. Checking one cavity is not anywhere near sufficient. Checking torque of the original keel bolts will be a difficult process, given the odd construction.

[Ken Fry]

Originally Posted by Cheechako

Maybe the metal is a tool for manufacture, not part of the actual keel?

No, it's not. The OP said that this was a modification to lower the keel by 4"

[Ken Fry]

Originally Posted by vic008

Explaining your concerns to the vender may well result in an amicable outcome.

Very likely. Generally contracts are written so that it is pretty easy for the buyer to walk away, with all deposit monies returned.

[stormalong]

Originally Posted by jeepers

If the Surveyor had access to this information doing the survey. He has accepted the responsibility. Confirm existence of his professional Insurance. Then likely so did the owner know of it. Whether they understood the ramnifications or not is irrelevant. Due diligence at that moment was on them. Your due diligence has uncovered this "custom" repair to the assumed original design, that you were accepting. It was after, that you received the photos.... Did the original Builder -Yard encapsulate this attachment in lead before installing the keel? Is the keel area both on the keel and hull essentially as original designed plans show. There maybe further deviations from the original as designed plans to accommodate this change. (Those changes might include a recessed area/pocket providing superior shear protection than originally designed.) Are there any as built plans from the yard? Your recourse after the fact should anything arise after delivery could involve the Owner as well as Surveyor & the original Builder/Boatyard if they made "unauthorized" changes to the as designed plans without changing the boats model name/number.

JEEPERS: Every survey I have ever had done contains a disclaimer of liability as it is just the surveyors opinion and there may be unseen issues. The surveyor has zero liability.

[Ken Fry]

Originally Posted by Muaddib1116

I'm not overly concerned with the structural strength of the steel frame as designed,

Perhaps you should be concerned about the stiffness more so than the strength.

The athwartship span between pairs of bolts looks to be 6"? You can change all these figures, but I'm going to guess 14,000 lbs in the keel, with the center of gravity of that being 3 feet below the top plate of the odd weldment. So when the boat is knocked down to mast horizontal, the steady-state moment at the plate would be 42000 lb ft. In the best case, the windward bolts will be under about 84,000 lbs load. One could test this in a shop with the keel removed, and a good sized hydraulic press, but my guess is that the deflection in the steel plates would be significant at that load, because the fore-aft span between cross bars is too large. If the deflection is 1/16 inch, then the sealant between the keel and stub keel would probably fail: certainly in those places where it is only a couple thousandths thick.

The fact that these pictures surfaced to answer the surveyor's questions suggests that the surveyor was seeing strange things. Surveyors virtually never ask a manufacture to provide such details.

You might want to talk with Mars Metals, who cast a lot of keels: Marskeel.com

[slug]

Originally Posted by Ken Fry

It is NOT a fact that "there is NO telltale signs of corrosion discoloration." Only the surveyor could say that, but he would be a fool to do so. The sump (the area inside the fiberglass stub keel) would have been thoroughly cleaned as part of the pre-sale cleanup. One could only assess corrosion, and especially crevice corrosion, by removing the keel nuts at this point, and examining the visible part of the bolts for corrosion.

You write: "the fact that it is MUCH more likely that any leakage of salt water into the fabrication below the stub keel would have come from water sitting inside the stub than through the fiberglass sheathing of the stub..."

Apparently, you do not understand the construction here. The fiberglass sheathing of the stub does not protect the weldment from water intrusion. The weldment is below the stub keel, and constantly submerged. The joint between the weldment and the stub would be sealed by any of the usual goops, any of which can leak. Then there is the fairing, that can also leak. No one has said what material was used to fair in the weldment. It could be hygrospopic body putty , hygroscopic polyester resin filler, foam, etc. It would be remarkable to find that the area around the original keel bolts is dry. It is the perfect environment for crevice corrosion. When the original keel bolts fail, they will likely do so suddenly, with the failure of one causing additional load on the next, etc. Think about how easily cloth tears if you start at an edge.

You write:
"I would say that the welds are likely to last your lifetime." Based only upon a fuzzy picture of a boat you have never seen? Wow.

You write:
"If you want further assurance, than a test by boring into any one of the cavities below the stub should either eliminate corrosion concerns or dictate that you test all the cavities."

Wrong. A good survey MUST check every keel bolt, not just a sample of one.
That means, in this case, that all the fairing material must be removed. Checking one cavity is not anywhere near sufficient. Checking torque of the original keel bolts will be a difficult process, given the odd construction.

Surveyors don't perform destructive testing , only observations

[donradcliffe]

Those were pretty clear pictures of the bolts inside the stub. If there was corrosion, there would be tale-tail bits of rust on and near the washers under the inside nuts. Getting it as clean as it appears would probably entail removing the nuts and washers, which is well beyond most pre-sale touchups.

OTOH, I watched Coyote (the Mike Plant Story) on Amazon Prime last night. They had a video clip of a very gentle grounding in the Chesapeake Bay, and then at the end a lot of shots of the bottom of the keel where the bulb broke off mid-Atlantic. I'd walk away from any boat from the same designer and builder.