Keel Failure in the Canaries

[jtsailjt]

Originally Posted by CarlF

I"ve never understood why bolt on keels aren't engineered differently to reduce the risk from keel bolt failure. Obviously it's cheaper, but boat builders often differentiate their product with superior build practices that cost more (e.g. watertight bulkheads). It seems folly to just bolt to a flat hull surface.

a) A 12" deep female socket molded into the bottom of the boat that receives the keel. Secured by horizontal bolts and vertical bolts.

or

b) A male and female bolt post with the bolt in the middle so that the bolt in only holding the keel up not handling longitudinal force such as a grounding.

or

c) keels cast with a threaded insert to receive a bolt that is screwed in from inside the boat - that can be removed and checked on a regular schedule without dropping the keel.

Has anyone seen boats with this or something similar?

Those all seem like good ideas to me.

Addressing "b." above, many full keels and conservative fin keels have a downward sloping interface from front to back so that in a collision with a rock, much of the force is transferred up into the hull through compression rather than being purely shear (and tension on the forward most bolt).

I'd imagine the reason that your ideas haven't already been adopted in a big way is that catastrophic failure is so infrequent that it's cheaper to just pay the low liability insurance premiums than it would be to make changes in the ways keels are attached.

[daletournier]

Originally Posted by arsenelupiga

Not funny at all.

I know and you know that you worry about what I said, because it is true.

99% chance you will be allright. Especially if you motor.

Actually the chances of him being OK are much greater than 99%. Your fear isn't necessarily another person's fear.

[robert sailor]

Originally Posted by jtsailjt

Ok, how about 1% +/- .99%? Close enough? Who knows what the precise number is, but to clarify, I meant the number of boats with bolt on keels whose owners might possibly have something to worry about enough to have the bolts inspected or replaced as a preventative measure, not that 1% of the keels were about to drop off on any given day.

For example, my last boat was a Nordic 44 with a long fin keel that was over a foot wide and was securely bolted on with several oversized looking keel bolts that could easily be seen at the bottom of the bilge and kept tightened. These boats are very ruggedly built and have no history of keels falling off. But the boat is now 32 years old so if I were still the owner, before crossing an ocean, I'd have the keel dropped and the bolts inspected and replaced as necessary just for my peace of mind. I'm not usually much of a worrier but am not willing to bet my life on some stainless steel that hasn't had a whiff of oxygen in 32 years! Of course if it had ever been hard grounded that's also a reason why I'd want it hauled and the ballast attachment inspected.

Fortunately Perry designs keel attachments to factors far in excess of modern boats so nothing to worry about, you could probably lose half the bolts and still be ok.
Now I completely agree with you regarding stainless steel bolts in iron keels or lead for that matter because they are subject to crevice corrosion. Some of the British builders used mild steel for that very purpose. They also tapped the keel so you could withdraw a stud one at a time to inspect it, this can be done on land or in the water. There is no reason to drop a keel on their boats unless the seal at the keel hull has been compromised then you probably should. Even after 30 years almost all of the owners who have pulled studs have found them like new but the odd one was rusted because the seal at the keel had been broken. The use of stainless steel is a marketing game because unlike mild steel the stainless looks good and people like shinny things.

[arsenelupiga]

Originally Posted by robert sailor

Not wanting to ruin your otherwise good post but if bolt on keels had a 1% chance of falling off you'd never get anyone sailing them. I don't know what the real number is but I can tell you it won't be anywhere near 1%.

think again. What is yearly number of boats perishing (ones that actually travel) - i believe 1 in 200. Keel failure would not get reported as all is over and under water in around 10 seconds.

1 % over lifetime of boat say 20 years seems quite reasonable number. You wont be able to prove or disprove as many boats simply perish. Keel falling off may me major reason for that.

[Polux]

Originally Posted by arsenelupiga

think again. What is yearly number of boats perishing (ones that actually travel) - i believe 1 in 200. Keel failure would not get reported as all is over and under water in around 10 seconds.

1 % over lifetime of boat say 20 years seems quite reasonable number. You wont be able to prove or disprove as many boats simply perish. Keel falling off may me major reason for that.

I have seen from time to time on boat magazines statistics about the cause of sinking of yachts. Losing the keel is just such a rare event that is not even mentioned, not having any statistic relevance.

Most sailboats sink or are abandoned due to water ingress due to varied reasons.

[billknny]

Originally Posted by arsenelupiga

think again. What is yearly number of boats perishing (ones that actually travel) - i believe 1 in 200. Keel failure would not get reported as all is over and under water in around 10 seconds.

1 % over lifetime of boat say 20 years seems quite reasonable number. You wont be able to prove or disprove as many boats simply perish. Keel falling off may me major reason for that.

I know you sail a catamaran and need stories of keels falling off monohulls to feel better--just like monohull sailors need stories about catamarans capsizing--but 1% of boats that are are sailing loose their keels? BOGUS.

Let's try some number just to see how "reasonable" it is...

A typical cruising boat has about 20 years where it is actually "out there" sailing. According to you, that means it has a 0.05% chance of losing it's keel in any given cruising year. So in a fleet of 100 boats, I would have--on average-- one boat losing it's keel every two years. In a fleet of 200 boats, I would average 1 boats losing a keel every year... but you claim that only 1 out of two hundred of ALL BOATS are lost from ALL CAUSES...

Add to this the fact that a very significant fraction of the cruising fleet CAN NOT have a keel fall off, either because they don't have one or it's fully encapsulated, or they have a full keel, or a very highly engineered keel that had a near zero chance of failure.

If you are going to claim that 1% of boats have their keels fall off, you need to present more data than your feeling that such a number is "quite reasonable" when a little thought shows that it is can not be so.

And I say all this, while thinking that a modern high aspect fin keel has no part of a ocean crossing cruising boat. It's just too likely to have a catastrophic failure. Cruising means going to out of the way places, and when you do that you WILL hit bottom. If your boat is such that after every grounding it needs professional inspection and repair, how will you go anywhere fun?

[a64pilot]

Originally Posted by SV DestinyAscen

There are a lot of French fast cruisers with lifting keels where the keel box is molded into the hull and a horizontal pin holds the keel in place with a hydraulic ram applying tension to the blade keel. Simple and uses leverage against movement.

From a structures and especially fatigue standpoint a bolt in shear is far superior to one in tension.
However as for example all of our cylinder heads are held on with bolts in tension, properly designed it does work.

Question I have is is it fatigue or corrosion that breaks these bolts.
Next one is every time you hear of a keel failure people come out and comment, well she must have been run aground before and not properly repaired.
Is it not reasonable to think a cruising Boat ought to be designed to sustain a grounding without harm?

[donradcliffe]

When you look at high performance bulb keels in race boats, the top of the keel has a fabricated flange which spreads the load across a transverse area several times as wide as the keel, reducing the stress on the bolts and the bottom of the boat.

The Cheeky Rafiki keel did not have a flange, and the narrow bolt spacing meant that the stresses were pretty high. I believe Xboats use a flanged keel. The Comet keel outline appears pretty high performance/high stress, and I am following with interest to see the details of the Comet keel attachment and failure.

[jtsailjt]

Originally Posted by a64pilot

From a structures and especially fatigue standpoint a bolt in shear is far superior to one in tension.
However as for example all of our cylinder heads are held on with bolts in tension, properly designed it does work.

Question I have is is it fatigue or corrosion that breaks these bolts.
Next one is every time you hear of a keel failure people come out and comment, well she must have been run aground before and not properly repaired.
Is it not reasonable to think a cruising Boat ought to be designed to sustain a grounding without harm?

Many cruising boats ARE designed to take a grounding without serious damage as long as it's not too hard. Almost all of the full keel boats as well as very many boats with conservative, long fin keels and skeg hung rudders also don't tend to get seriously damaged in a grounding. When I was in the Bahamas with my 7' draft Nordic 44, I "touched bottom" almost every time I left the slip but fortunately it was soft sand and didn't even seem to affect the bottom paint too badly. It's mostly just when you get into higher performance, high aspect, skinny, fin keels that you can expect damage from any time the keel hits anything. High aspect keels are great for performance, but that long moment arm combined with small area where the forces are concentrated and the need to keep the hull as light as possible, means that it's a LOT less forgiving arrangement.

I think that part of the problem is that lots of folks in the boating industry have been willing to embrace evolving the definition of "performance cruiser" to apply to boats that really aren't cruisers at all. They should probably be more correctly labeled performance day sailors with living accommodations inside. Advertisers pay the bills of the sailing magazines so they call the tune. I used to know one of the "boat of the year judges for one of the most well known sailing mags and when I read his evaluations of some of the boats that won I KNEW he wouldn't be caught dead attempting to cross an ocean in them. He's spent his whole life living aboard, has circumnavigated almost twice, and had some pretty conservative ideas about what made a good cruising boat, but he was being paid by a ""cruising" publication to heap praise on boats that were nothing like what he preferred to cruise in or privately said he would cruise in, so that's what he did. He has to eat too.

You get a lot of sailing "bang for your buck" from a lightweight boat with an aggressive fin keel and spade rudder, but they don't do very well when you bump into something you didn't intend to. Back before we all had chart plotters and Loran coverage wasn't real great either, during one particularly foggy June, our local boatyard in Maine had 3 boats hauled out and on stands that they'd had to haul quickly because they'd hit ledges and were leaking. All 3 had pretty aggressive keels and I remember inspecting them and thinking how remarkably similar the damage was. They all had the very narrow trailing edge of the keel driven right up into the hull with a crack or two emanating towards the stern, it made me think of an eggshell. Then I started wondering how you could possibly repair something like that without tearing the whole inside of the boat apart, and THEN I started wondering what that grounding that would barely have affected a "lower performance" design was going to cost to have repaired. Luckily, all 3 had their misadventure with a ledge close to full service marina so nobody died, but what if they'd been cruising in a remote area even a few hours from a haulout? They'd have surely lost their boat due to an event that would have been merely a bit embarrassing to the skipper of a lower performance but more traditional cruising boat.

[Jim Cate]

It is completely possible to design and build a modern fin and bulb keel that will absorb grounding loads without damage to the structure as Don R points out above. It is less possible to do so and compete pricewise with Beneteau et al who don't spend the extra time and money on doing so. The result of the price war is keels like the Cheeky R. They are most often adequate, for most boats are seldom sailed and even more seldom highly stressed, and the bean counters are happy with the bottom line.

The serious cruiser has different needs, and surviving a severe grounding without immediate slipping is one of them. I reckon that such a sailor must either pay the differential for higher quality construction in a modern keel or suffer the performance hit of a less efficient shape. For us, the compromise was a more conventional fin, and one of very robust construction. The boat will easily stand upon it, well balanced, so drying out against a wall or even careening is feasible. The lift/drag ration isn't as good as it could be, but on the other hand, the shape is more forgiving and does not stall easily... and so far, it has survived numerous soft groundings and one rock strike with no damage beyond a small ding in the leading edge (steel shell, lead inside).

So, in my view, all the blanket condemnation of fin keels for cruisers is pretty indefensible and should be evaluated as such. To be rational about choice, one needs to examine each specific design with care and consideration of how loads are absorbed. Not an easy task, but then, who said choosing a boat for serious cruising would be easy?

Jim

[u4ea32]

Originally Posted by GTom

Wow, great news that it didn't end up in a tragedy and the entire crew are safe! Indeed it pushes my upcoming boat buying decision to encapsulated designs. Even though encapsulated keel boats are not as fast and the encapsulated iron might start rusting at the age these boats usually are (30+years), leaving the owner with a much more complicated repair than a few new keel bolts. True however, I've never ever heard about an encapsulated keel failing at sea capsizing the boat and killing her crew as several bolt-on keels did in the past decade.

I saw a Cal 48 (encapsulated lead) being repaired, where the glass at the aft end of the keel was very, very poorly laminated: there was essentially a single layer of glass keeping the water out, with the other thick layers of woven roving pretty similar to dry burlap. Probably a 4:30PM on Friday lamination job. The fact the boat survived several decades did not mean that serious flaw was not waiting to kill the crew. It certainly was! But the long fin keel (by modern standards), low modulus construction, and overall flexibility of the boat kept loads from being concentrated to the point of failure. Still, if the owner had not more-or-less capriciously decided to poke a new hole in the bottom (new shaft? new thru-hull? I forget), this dangerous flaw would not have been discovered in the shipyard.

Flaws are lurking in all systems. Very high load makes failures more likely, even if the boat otherwise seems in perfect condition and well proven. High loads cause degradation that is often invisible: fatigue, delimitation, micro cracking, corrosion in metal because coatings are damaged, and so on.

[jmaja]

Originally Posted by Jim Cate

It is completely possible to design and build a modern fin and bulb keel that will absorb grounding loads without damage to the structure as Don R points out above.

If by "modern fin and bulb keel" you mean something quite similar to keels for First 40.7 and Comet 45S, I don't think it is possible to design and build them to absorb all grounding loads without damage.

They already are able to absorb some grounding loads and it is possible to make them able to absorb even more. But these boats sail upwind 7 knots and can easily do 8-10 knots in other points of sail. Surviving a full stop from that speed is just not possible without structural damage unless you have a very special system taking care of all that energy. Like Linjett 43 has with lifting keel.

[Jim Cate]

If by "modern fin and bulb keel" you mean something quite similar to keels for First 40.7 and Comet 45S, I don't think it is possible to design and build them to absorb all grounding loads without damage.

I think you have missed the point here. The keel on the First 40.7 is simply bolted through the rather thin hull and the internal molded grid, relying upon fairly small washer-like metal bits to resist pulling through during a ground strike.
That is what failed in the Cheeky R event, and previous grounding has been mentioned as a cause for the failure.

Other boats, for instance ours, have far stronger structures to which the keel is bolted. These structures are more expensive and more intrusive into the hull volume than the Beneteau approach is. It is my position that if such provisions are made in the design, the need for slipping and examining the hull to keel joint after any grounding is eliminated. It costs more and may compromise the keel shape somewhat, but it is possible to achieve.

Jim

[GTom]

Originally Posted by u4ea32

I saw a Cal 48 (encapsulated lead) being repaired, where the glass at the aft end of the keel was very, very poorly laminated: there was essentially a single layer of glass keeping the water out, with the other thick layers of woven roving pretty similar to dry burlap. Probably a 4:30PM on Friday lamination job. The fact the boat survived several decades did not mean that serious flaw was not waiting to kill the crew. It certainly was! But the long fin keel (by modern standards), low modulus construction, and overall flexibility of the boat kept loads from being concentrated to the point of failure. Still, if the owner had not more-or-less capriciously decided to poke a new hole in the bottom (new shaft? new thru-hull? I forget), this dangerous flaw would not have been discovered in the shipyard.

Flaws are lurking in all systems. Very high load makes failures more likely, even if the boat otherwise seems in perfect condition and well proven. High loads cause degradation that is often invisible: fatigue, delimitation, micro cracking, corrosion in metal because coatings are damaged, and so on.

Allright, but what happens if all goes bust and that glass develops a big hole in the middle of the ocean? You take a few pictures, get your warm chlotes on, drink a last hot tea, call mayday and abandon to your liferaft. And what happens if you loose a bolted keel? you capsize in a second, break an arm, loose a few crew members and if you are very-very lucky you can make it to your liferaft.

[Jim Cate]

And what happens if you loose a bolted keel? you capsize in a second, break an arm, loose a few crew members and if you are very-very lucky you can make it to your liferaft.

Yep, happens every day. Dunno how anyone could go to sea with a bolted on keel.

Jim