Keel Failure in the Canaries

[GTom]

Originally Posted by Jim Cate

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

Jim

Would cause enough headache if happens me just once in 30 years...

[u4ea32]

Originally Posted by jmaja

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.

I agree the Linjett 43 has approached this problem very well.

However, its not that hard to make thick fiberglass absorb lots of energy. Fiberglass, especially if laminated with epoxy or vinyl ester, can absorb enormous amounts of energy before failure. Its really the key reason fiberglass boats seem to last forever: the structure stretches a little, so the entire laminated structure absorbs the load.

The problems occur due to two reasons. Perhaps the most common is when designers and builders try to save money on construction by using enough fiberglass for the normal loads of sailing, rather than enough to absorb groundings. These are very different load cases, and therefore require very different amounts of fiberglass.

The second reason is that performance is closely related to stiffness: the stiffer the structure, the more energy goes to forward movement, and the more flexible the structure, the more energy is absorbed by the structure (tiny amount of heat). Like pushing on jello will deform the jello rather than translating (moving) the entire blob. But stiffness means the structure will absorb LESS energy before failing.

A high impulse load, like a grounding, with a very stiff structure can cause the structure to fail rather than deform.

But also, the concentrated high loads of a stiff structure will lead to those invisible defects, such as delimitation, micro cracks, etc. These invisible, gradually expanding defects, can then fail with little warning.

[jmaja]

Originally Posted by Jim Cate

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.

I don't think I missed the point. You claimed that it is possible to have a modern fin keel which will get no structural damages from groundings. I don't think that is possible, if you include groundings with typical sailing or motoring speeds to objects that stop the boat without damping. Most boats can survive a low speed grounding or a grounding to soft objects like sand or mud without structural damage.

I'm not saying that 40.7 has a perfect or even a good keel structural design and there certainly are similar keels with much better structural desing. I'm not that familiar with Comar, but it probably has a clearly better design.

We have a lot a granite grounds here in Finland and boats made here are certainly designed to hit one sooner or later. Still even the sturdy ones get structural damage from some groundings.

[jmaja]

Originally Posted by u4ea32

I agree the Linjett 43 has approached this problem very well.

However, its not that hard to make thick fiberglass absorb lots of energy. Fiberglass, especially if laminated with epoxy or vinyl ester, can absorb enormous amounts of energy before failure. Its really the key reason fiberglass boats seem to last forever: the structure stretches a little, so the entire laminated structure absorbs the load.

Note that his keel is an option for Linjett 43. The standard is a fixed keel, which would not have survived these groundings although it is certailnly one of the most tolerant ones with that kind of keel.

As you said there is a dilemma of having the stucture stiff and absorbing at the same time. You really can't have both at least without structural damage while grounding hard. Modern fin keels need a stiff structure in order not be wobbly and also not to cause fatigue due to constant wobbling while sailing.

When hitting a ground that provides no dampening all the dampening must come from the structure. I don't think it is possible for the floors to provide that without causing local overloadings and thus structural damage. A very thick GRP without floors could be sufficient

I know one boat that has that kind of structure. It is Dominant 78. Here is an article in Swedish. It was run many times to a hard granite ground at a bit over 6 knots without structural damage. But it doesn't have that modern keel (only 1.35 m deep), it's quite small (7,8 m, 1,7 tonnes) and it has 40 mm GRP hull at the keel area without floors.

How thick would that need to be for a 40-45' boat at 7-10 tonnes and 2,5 m deep modern fin keel running to a hard ground at 8 knots? There is about 10 times more energy to be absorbed and the keel has about double the leverage.

[Seabeau]

Seriously folks, you're trying to reinvent the wheel. The simple solution is to return to configurations that the sailing fraternity left a hundred years ago in the quest for better windward ability, which imho is highly overrated in terms of overall cruising ability. Centerboards, daggerboards or lifting keels. My vessel, designed in 1884 is a centerboard equipped Presto 36, which drafts 2-6" BU, is designed to "take" the ground upright and has no external keel aside from its external 6"X9"X20' lead grounding shoe, with the remainder of the ballast molded into the bilges.

[jmaja]

Even traditional long keeled boats can loose their keel, if not taken good care of: FREUNDESKREIS KLASSISCHE YACHTEN

[arsenelupiga]

Originally Posted by Seabeau

Seriously folks, you're trying to reinvent the wheel. The simple solution is to return to configurations that the sailing fraternity left a hundred years ago in the quest for better windward ability, which imho is highly overrated in terms of overall cruising ability. Centerboards, daggerboards or lifting keels. My vessel, designed in 1884 is a centerboard equipped Presto 36, which drafts 2-6" BU, is designed to "take" the ground upright and has no external keel aside from its external 6"X9"X20' lead grounding shoe, with the remainder of the ballast molded into the bilges.

absolutely !

and windward ability has become so overrated, to counter multihull abilities. And it doesnt even work. Boats start breaking if trying too hard. Pretty stupid reason.

[boatman61]

Originally Posted by Polux

Can you elaborate on that? A keel that fall off at a marina? or was just some bolts that broke? On the marina?

My first boat.. a timber Magyar 7 bilge keeler had one of its keels fall off/come away while alongside.
I'd done a last end of season crossing to Cherbourg and sailed into Keyhaven late evening and was due to be lifted for the winter the next morning..
When I got back to the yard at 0800 the next morning she was sitting on the bottom with her decks awash.
The stbd keel had come away and she'd flooded as the tide rose..
A lucky thing it did not happen halfway across the Channel.

[daletournier]

Originally Posted by jmaja

I don't think I missed the point. You claimed that it is possible to have a modern fin keel which will get no structural damages from groundings. I don't think that is possible, if you include groundings with typical sailing or motoring speeds to objects that stop the boat without damping. Most boats can survive a low speed grounding or a grounding to soft objects like sand or mud without structural damage.

I'm not saying that 40.7 has a perfect or even a good keel structural design and there certainly are similar keels with much better structural desing. I'm not that familiar with Comar, but it probably has a clearly better design.

We have a lot a granite grounds here in Finland and boats made here are certainly designed to hit one sooner or later. Still even the sturdy ones get structural damage from some groundings.

I think it is possible . Not all fin keels are created equally. My last boat was a Freedom 32, lead bolt on keel. We can argue whether or not they can take a beating or we can test it in the field.

Unfortunately I chose the later, accidently! I motorsailed into a rock or reef at approx 4-4 1/2 knots, came to a complete stop that send me flying. I was sure I had done some serious damage, I straight away check bilges, fortunately all was well. I was 20mins from marina in Malaysia therefore I pulled in. With this boat I had complete access to the inside of the hull so was able to carefully check for damage, there was no evidence of any sort smiley hull deformation. I hauled the boat with a crane to thoroughly check the bottom, besides from a decent dent in the lead and a little fairing issue there was no damage.

I think I mentioned earlier in this thread that my current boat has a lead keel, a keel stub and a strong glassed in grid structure, my previous experience made this very desirable, absord impact and then distribute what's left over a greater area rather than just concentrate all impact to a single area.

My point is I've tested a lead bolt on keel at speed against a immovable object and didn't sink or damage the boat structurally .

[daletournier]

Originally Posted by Seabeau

Seriously folks, you're trying to reinvent the wheel. The simple solution is to return to configurations that the sailing fraternity left a hundred years ago in the quest for better windward ability, which imho is highly overrated in terms of overall cruising ability. Centerboards, daggerboards or lifting keels. My vessel, designed in 1884 is a centerboard equipped Presto 36, which drafts 2-6" BU, is designed to "take" the ground upright and has no external keel aside from its external 6"X9"X20' lead grounding shoe, with the remainder of the ballast molded into the bilges.

I'm familiar with your boat, I like them mainly due to liking stay less masts BUT it wouldn't be my first choice crossing oceans. And from what I remember a cat boats design breed was not this, happy to be corrected.

Either give me form stability in the form of a multi or a whole lot of ballast stability down low preferably in lead.

[Pete7]

Originally Posted by Seabeau

Seriously folks, you're trying to reinvent the wheel.

Or just don't worry about it. How many yachts around the world have bolt on keels and how many of those yachts loose a keel each year.

Anyway we all carry life rafts offshore don't we? I'll get my coat.

[Island Time O25]

The very first season of my boat ownership I touched rock ledge which was submerged at mid/high tide. The boat was an early 80s production 27 footer with bolt on fin keel. There were two hard bumps on the keel and one lesser bump on the rudder. My first immediate reaction was to run below and check the bilge. After a few minutes and much adrenaline pumping I was satisfied that the water will not be gushing in and so I motored back to my mooring, about 20-30 minutes away. Next few days were uneventful and as this was mid August I decided to keep her in the water until the scheduled haul out in late October. Come October haul out, I see two fist size dents on the bottom of the keel and I also see that the rudder stock is slightly bent, bringing the top of the rudder within millimeters of the hull, instead of 1/2"-3/4" clearance. Next Spring my boat building buddy examined the whole thing and declared damage minimal and not requiring extensive repairs. Since this was a $400 "training boat" and I was then on a very tight budget any repairs over $500-1000 would be out of the question. So I went with my buddy's advice and we shaved off and re-glassed the top 3/4" of the rudder and left the stock as is. The boat gave me another 3-4 happy seasons of sailing and was sold with an explanation of what we did or did not do post that grounding. The buyer couldn't care less as this was also for him a training boat and the price was right.

Another related aside. A few years after that grounding I was changing the depth sounder with the help of the same boat builder-buddy. He was very surprised to see that near the keel stub there was about an inch or more of laminate and it was in like new condition as we took off the sounder. This turned out to be a much better than average built boat from a builder never known for great quality. I was intrigued as to why and did a little research. What I found was very interesting as the search results explained the quality build from a builder not generally known for quality. Turned out that when Bayliner bought US Yachts back in late 70s or early 80s, to satisfy then growing demand they expanded USY to 3 plants. One plant was staffed entirely by old USY hands, incl. the management, one was a mixture of old hands and new ones and the third was staffed mostly by Bayliner workers who were used to producing chopper gun soap boxes. So consequently each plant produced totally different quality boats even though all of them looked the same when new. And of course it were the "bad plant" builds which gave the "bayliner" reputation to the USY brand. The boats built in the "good plant" could easily compete with Pearsons and Sabres as far as quality of construction was concerned. But this never became known until much later when the bad plant built boats started falling apart while the good plant built ones were still going strong.

This was quite a discovery for me - that the same brand output can be so different. And that for the same model one plant will use traditional cloth and roving, backing plates, etc., while another plant will just use a chopper gun, thin washers, etc. Perhaps this is a textbook example of how not to run a company if you want your brand to last.

[Seabeau]

Originally Posted by daletournier

I'm familiar with your boat, I like them mainly due to liking stay less masts BUT it wouldn't be my first choice crossing oceans. And from what I remember a cat boats design breed was not this, happy to be corrected.

Either give me form stability in the form of a multi or a whole lot of ballast stability down low preferably in lead.

Perhaps you're not familiar with my boat. It does not have stay less masts. Of course you might be thinking about Munroe's Egret which does have stay less masts. My boat is a boat designed by Ralph Middleton Munroe in 1884. Wikipedia has a small piece on him.

[daletournier]

Originally Posted by Seabeau

Perhaps you're not familiar with my boat. It does not have stay less masts. Of course you might be thinking about Munroe's Egret which does have stay less masts. My boat is a boat designed by Ralph Middleton Munroe in 1884. Wikipedia has a small piece on him.

OK, I'm mistaken, can you sent me a link? I like boats.

[daletournier]

Originally Posted by Seabeau

Perhaps you're not familiar with my boat. It does not have stay less masts. Of course you might be thinking about Munroe's Egret which does have stay less masts. My boat is a boat designed by Ralph Middleton Munroe in 1884. Wikipedia has a small piece on him.

OK, I'm thinking of the Presto 30, which I think is a great little boat.