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Old 17-02-2015, 13:13   #1
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Why do Keels fall off and rudders fail?

I have been in the thread about blue water boats going extinct and to some degree I think that the production designs have veered away from what could potentially be a blue water cruising boat.

I read on this forum and others about newer designed boats where the spade rudder bend, fall out........ why does this happen? Design, material, corner cutting? I personally haven't been a victim of such am event so I thats why I am asking

Same with the keels,I see pictures of boats turtled because keel just fell off. Again I have not had this happen so I ask why? why are these things happening?

I know if I bought a $250K(or more) vehicle and it drove just fine around town but the first time I decided to cross the country has bit a bad patch of road the engine fell out or steering wheel came off in my hands Id wonder WTF? Not only that why do I see parking lots(marinas) full of vehicles just like mine. To top it off every dealer in town has vehicles that are designed just like the one that left me stranded.

I guess I am asking why or how are these builder still selling new boats with what seems to be dangerous design for rudder and keel?
I am not bashing simply asking what the main causes have been and how are the boat builders working to prevent these failures in the future?
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Old 17-02-2015, 13:14   #2
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Re: Why do Keels fall off and rudders fail?

It happens almost as often as steering wheels fall off of cars.

It just gets picked up on comment boards and recycled more often.
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Old 17-02-2015, 13:26   #3
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Re: Why do Keels fall off and rudders fail?

One of my rudders "failed" back in 2008. It was foamed filled, as many are, and the fiberglass casing had apparently been leaking over a long time such that the foam become saturated and weakened. Too much sail up one day and in a puff with a lot of weather helm the stbd rudder blade twisted right off the stock. Spin out. So I can claim I sailed the rudder right off the bottom of the boat. I'm not too proud to admit that I didn't know the rudder blade had fallen off and I spent the next 8 or so days of sailing trying to figure out what was wrong with the auto pilot.....

Keels falling off? What's a keel?

Dave
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Old 17-02-2015, 13:36   #4
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Re: Why do Keels fall off and rudders fail?

The analogy with a ground vehicle is valid: a "normal" car should be able to cross a bad patch of road. But you don't expect it to go full speed off-road, which is equivalent to sailing in a storm.

It is very difficult for a naval architect to estimate the forces acting on a keel or a rudder in *very* bad weather. Then, the normal solution is to include a *big* margin (for example 500%). But this is costly and heavy. The real market for these sturdy, heavy and expensive yachts is narrow.

The other phenomenon is the meeting of a slight design error, a small manufacturing error, a lapse in quality control and severe conditions.

Alain
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Old 17-02-2015, 13:42   #5
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Re: Why do Keels fall off and rudders fail?

i tend to blame everything on saltwater these days...
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Old 17-02-2015, 13:46   #6
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Re: Why do Keels fall off and rudders fail?

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Originally Posted by Hydra View Post
The analogy with a ground vehicle is valid: a "normal" car should be able to cross a bad patch of road. But you don't expect it to go full speed off-road, which is equivalent to sailing in a storm.

It is very difficult for a naval architect to estimate the forces acting on a keel or a rudder in *very* bad weather. Then, the normal solution is to include a *big* margin (for example 500%). But this is costly and heavy. The real market for these sturdy, heavy and expensive yachts is narrow.

The other phenomenon is the meeting of a slight design error, a small manufacturing error, a lapse in quality control and severe conditions.

Alain
Given that peoples lives are on the line( being in the water and all) shouldn't builders build the fudge factor into these boats.
Are boats today over engineered to the point they are under engineered.... if that makes any sense? Basically engineered to the edge so much so that any mistake in any of the processes creates failure? if so, why is this being done? no data guessing, can't see that? They know what has worked for hundred of years of sailing....Is it money and cost of materials, the bottom line $$? I can see that.
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Old 17-02-2015, 14:02   #7
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Re: Why do Keels fall off and rudders fail?

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Are boats today over engineered to the point they are under engineered.... if that makes any sense?
It's much more simple: many details aren't engineered at all! The design office makes a raw sketch and the yard makes an assumption.

If you want a proof that a boat has been engineered and built according to rules, get one built under control of a class society (e.g. ABS, Germanischer Lloyd...).

Alain
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Old 17-02-2015, 14:15   #8
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Re: Why do Keels fall off and rudders fail?

Rudder stocks are prone to corrosion at the bearing where the shaft enters the hull. Can only be discovered by dropping the rudder which is seldom done.

The new boats with ultra short keels with huge bulbs at the bottom have very little area where they attach to the hull. Huge stresses concentrated in a small area. Doesn't take a small mistake in design, construction, stress from grounding, and/or construction for the keel to say sayonara
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Old 17-02-2015, 14:20   #9
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Re: Why do Keels fall off and rudders fail?

Hello,

I think the keels and rudders falling off pertain mostly to racing, where designers push the envelope. Lack of maintenance would account for it too. However it does happen once in a while on cruising boats, and lives have been lost to broken keels.

Here is the latest example I know of:
Keel missing from the hull of Cheeki Rafiki | Meridian - ITV News

So, why risk it when you can get a full keel boat and never have to worry about it? Sure, you might be a bit slower, so what?

It is a matter of personal standards. It isn't only boats. Some airplanes can't recover from spins.. FAA solution: Spins are not allowed with those airplanes. Right... I won't fly those (like the Piper Tomahawk). Others have no problem flying them. Same for boats.

Gil.
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Old 17-02-2015, 14:54   #10
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Re: Why do Keels fall off and rudders fail?

I think that most rudders and keels that "fall off' had owner help somewhere along the way.
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Old 17-02-2015, 15:58   #11
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Re: Why do Keels fall off and rudders fail?

Global warming

Poor design, lack of maintenance, poor quality control, using a boat beyond the scope of its design, damage, premature failure, unscrupulous builders, collision, rank amature owners deciding what is seaworthy, etc, etc, etc,
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Old 17-02-2015, 16:05   #12
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Re: Why do Keels fall off and rudders fail?

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Global warming
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Old 17-02-2015, 16:23   #13
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Re: Why do Keels fall off and rudders fail?

Keels wont fall off a steel or alloy boat,Pretty sure rudder wouldnt either.Have owned a glass boat whose keel rocked side to side while getting waterblasted on travellift.Fixed it with 2 huge laminated frames inside keel stub,was still nervous about it though.
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Old 17-02-2015, 16:34   #14
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Re: Why do Keels fall off and rudders fail?

Wow. I'm the only one who admits to a rudder/keel failure. I'm honored and humbled to be a "rank amature" among so many who have never experienced a component failure. Could it possibly be because I leave the dock?

"Amature", indeed.

Dave
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Old 17-02-2015, 16:38   #15
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Re: Why do Keels fall off and rudders fail?

I can only speak from one occurrence when I was crewing on a large "maxi" on a delivery and the rudder snapped off. We too argued for a little while as to whether or how much had fallen off. In the end we had no realistic way to rig a rudder and ended up getting towed by a passing freighter. We had not broached or fallen back on a wave. The boat was not even a year old. We had been beating to weather for about 5 days though in steep chop and the whole boat had been pitching and slamming that flat hull pretty hard. That boat had a huge spade rudder but to me now all spade rudders look like a weak link. They are great, necessary, for racing, but in racing you are prone to pushing limits to get a few more knots or to point a little higher and you accept the risk. To take that same philosophy to a cruising boat is not wise I think. There is just a lot of stress on that one point in the rudder post. It is not a wise thing to design from an engineering standpoint, but it is great for speed. There is probably a thread about the stress loads on a spade rudder vs. a skeg or keel hung rudder. And I know people are cruising around the world successfully with spade rudders but personally I'd say bring a spare rudder to hang on the transom!
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