Hunter Rudder loss

[Guest]

There was a well reported case of a Hunter loosing its rudder in the Atlantic.....

Did Hunter follow this loss up in any way, did they accept blame in any respect.
I also lost my rudder about one year before the atlantic incident in my hunter 340, with no major problems, except total loss of directional control. I forwarded photos of the sheered stock to Hunter, this clearly showed, IMHO, defects in manufacture, but they declined responsability. ""These defects in the lamination were in no way responsable for the failure"". I think I struck an underwater obstruction, whilst under way. under motor but with no helm applied. The failure happened a few hours later, under way, with full sail.

Has any one else had this problem, and been assured this was a one off, and in no way related to the manufacture......

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[Jacket]

There was a reply from Hunter about it in last months YW. Why not send a copy of the photo's to YW, they may be interested in following it up.

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[AndrewB]

Like this one, perhaps?

Hunter 376 rudder

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[vyv_cox]

Re: Like this one, perhaps?

Fascinating photograph. With a working lifetime spent diagnosing engineering failures, although not necessarily in composites, I would say:

1. No evidence of lateral impact
2. Clear evidence of bad bond between the stock and rudder
3. Transverse fracture. This is the most important feature as it indicates brittleness. Engineering components are virtually never intended to fail in a brittle mode because the force required will be low and unpredictable. If they fail the fracture should be ductile due to overloading at a suitable safety factor. With composites the fracture is mixed mode ductile and brittle, normally a jagged, progressive rupture such as occurrs in wood.

I would have little hesitation in saying that the stock in this photograph failed due to inadequate material properties brought about either by poor manufacture or poor selection for the environment in which it was to operate.

No comment on spade rudders - another contributor to the problem.

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[Jacket]

Re: Like this one, perhaps?

I'd generally agree, except to state that there is some indication of impact. The back of the top of the rudder has compresion damage, suggesting that the bottom of the rudder hit something, forcing the trailing edge of the top face up into the hull.

At a guess I'd say the rudder was lost after the yacht ran aground. As the tide went out, the weight of the yacht slowly came onto the rudder (many boats seem to have rudders not much shorter than the keel, making this problem common) until it snapped off. that would explain the lack of inpact damage.

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[AndrewB]

Re: Like this one, perhaps?

I think that's probably correct. The photograph on the water's edge suggests a grounding. The picture came from a posting on <A target="_blank" HREF=http://old.cruisingworld.com/forums/genlmesg/index.pl>CWBB</A> a few months back, and regrettably I made no note of the circumstances, but it could probably be traced through the archives.

Since concerns that the RCD provides no specifications on structural integrity, and that some production builders have been building hulls lighter and to lower standards possibly in consequence, I've been collecting reports from boards of major structural failures on modern production yachts, excluding the mast and rigging. The commonest problems seem to concern the hull-keel join and the rudder stock; the hull/chainplate attachment and the bow plate/forestay attachment also crop up.

 

[Badger]

Leg End

I wish you would't call them Hunters but Legends. It could be confusing to people considering buying a proper boat like a British Hunter.

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[Twister_Ken]

Don\'t blame the RCD

I'm not sure that the RCD has anything to do with this, though.

From pre-RCD days, I'm aware of a couple of OOD 34s that had problems caused by panels 'panting' in the forward sections, of a Sigma 33 that lost her keel on the Brambles bank, and a Sigma 36 that had the keel punched into the boat on Exemouth Bar.

Rudder loss has never been unusual, even if thankfully it is not common. Witness all the articles written about rigging jury rudders, or about sailing without one.

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[vyv_cox]

Re: Like this one, perhaps?

I wouldn't have called that "impact", by which I meant collision with something while moving. I would agree that damage during grounding is a very likely cause but the fracture face looks very suspicious to me. Grounding could be expected to apply high lateral loads to the rudder stock which, if correctly engineered and constructed, should fail in ductile (or composite equivalent) overload.

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[Jacket]

Re: Like this one, perhaps?

There is no composite equivalent of ductile behaviour- it always exhibits brittle behaviour. This is one reason why structural engineers are still wary of using composites- current design methods rely on the ductility of steel and reinforced concrete (yes, it is ductile if properly designed) to overcome the problem posed by the fact that it impossible to know the true stress state of most structures.

Instead, it is necessary to design for brittle behaviour. Yes, a composite rudder stock will snap off if hit hard enough. However, a steel rudder stock would buckle and jam the rudder if hit equally hard, so the difference in behavior still results in similar problems.

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[vyv_cox]

Re: Like this one, perhaps?

Not quite correct. Without wishing to indulge in technical arguments about such things, composites fail in a progressive manner if constructed correctly. Ever chopped any wood? Or seen a GRP boat that got T-boned? Neither fails in a brittle manner. I agree that on a micro scale there is brittle mode fracture but not on a macro scale. Equally true of steels.

Main reason that engineers of all persuasions don't like composites is that it is vitually impossible to non-destructively test them. So there is no way of telling whether they have been made properly.

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[andy_wilson]

Of course it's related to manufacture. If they built the stock twice or three times as thick it would be much stronger and less likely to let go.

Whilever all manufacturers tread a fine line between slimness and strength, RYA courses will bang on about sailing without rudders or with jurry rudders.

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[Jacket]

Re: Like this one, perhaps?

Sorry, but I disagree. No matter how its designed, composites cannot fail in a ductile manner. The situations you describe are not ductility, at least not in a technical sense. Ductility does not just mean that a material can deform without breaking. The important point is that it can deform without any loss in strength.

Composites cannot do this. Yes, the GRP of a T-boned boat may deform, but the area of impact is far weaker than it was before impact.

This very different behavior is vital, especially under structural loadings. Imagine a steel beam, which is being loaded up. When it reaches its maximum strength, the beam starts collapsing, but with no loss of strength- remove a tiny fraction of the load and the bridge will stop collasing. This behaviour is vital in the design of structures to withstand overloading, as it allows elements within a structure to deform, and shed excess load to adjacent parts of the structure.

By comparison, once the fibres in a composite reach their maximum load, they snap. Imagine a bit of composite under tension. You load it up till a fibre within the composite reaches its maximum strength, at which point it snaps. the load that was carried by that fibre then has to be distributed amoung the other fibres, which are already near their maximum strength. This additional load causes more fibres to snap, the remaining fibres have to carry more load, and so on. Brittle failure. there is no way around this problem.

The significance of this is that the result of impact will be different in the case of properly steel and composite rudder stocks, but the net result will be just as serious. While a large impact willsnap off a composite stock, it will bend a steel stock to a degree where the rudder will be jammed, and the hull will be punctured by the rudder. In other words, in this case, ductility is irrelevent- once ductile behaviour has occured, the rudder stock has failed anyway.

Finally, the inability to carry out non destructive testing (NDT) on composites has little relevance to structural engineering, at least on large structures. Steel can be tested, but the cost prehibits it on most structures. Also, determining the significance of cracks and the like is a very subjective skill. Meanwhile there is no effective way of carrying out NDT on reinforced concrete structures. Indeed, the first person who comes up with a cover meter (a device that can tell you the position and depth of steel within the concrete, as well as the degree of deterioration to the steel) will make millions (I'm working on it!).

This lack of ability to NDT concrete does not stop its use. The two factors that are preventing its use are cost (which is reducing thanks to the use of mass produced prefabricated units) and more importantly its lack of ductility which makes safe design a bit of a lottery (Having met most of the small number of engineers currently involved in the design of composite bridges in the UK, I'm still unable to decide whether they're exceptional and pioneering engineers, or just plain stupid).



<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by Jacket on 21/05/2003 10:10 (server time).</FONT></P>

 

[Guest]

Firstly I must say sorry to the Hunter UK owners and correct the headine to LEGEND.

I had the rudder loss in 2001, and was very lucky it was in close costal waters.
I am trying to post three photos, but can not see how to attach these.....help.

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[vyv_cox]

Re: Like this one, perhaps?

NDT is avoided in concrete and steel construction by ensuring that manufacture is strictly controlled to established standards. No such standards exist for composites. When we began to develop and use glass-reinforced epoxy pipework we developed our own procedures and only allowed companies who could apply them to produce for us. There are only two world-wide. Even so, there are occasional failures.

On the brittleness/ductility argument I am referring to the failed rudder stock. The situation you describe is what I called a progressive fracture. It would have a rough and jagged appearance, like a snapped stick or a T-boned yacht. Not the flat, smooth appearance shown in the photograph.

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[Jacket]

Re: Like this one, perhaps?

I'd still like to hear how you get ductile behaviour from composites. Millions are spent every year trying to acheive this feat, as it would vastly increase the possibilities of the material. Though possibly coming from different areas of engineering we're working to different definitions of ductile.

On the rudder stock in question, we really nead to know more about the events causing the rudder loss. If the rudder was hit side on, causing the rudder stock to bend and fail that way then I agree that it should exhibit a rough and jagged failure surface.

However, if it was hit from ahead, I'd expect things to be different. Provided the hull and rudder are strong enough the rudder stock can nolonger bend, as the back of the top face of the rudder pushing against the hull prevents this. In this case the stock is being sheared by a scissor action between the rudder and the hull, and I'd expect a much cleaner failure surface. I think the dammage visable to the back of the rudder makes this second scenario the more likely.

While manufacturing flaws may have led to failure, I think that they'd only be noticable from a much more detailed examination than is possible from the photo. the aspect of composite rudders that worries me is not impact resistance, but fatigue. However, this failure does not look like that.

As a side issue, NDT is not avoided for concrete through he use of strictly controlled standards. Yes, the standards do exist, but the reality is that they are very hard to enforce. It really is scary some of the things you hear of being done on construction sites. On top of this, it has to be recognised that concrete is a very variable material. Even under ideal lab conditions, I don't expect the strengths of two supposedly identical batches of concrete to be much closer than 15-20%. Safety is obtained through the use of very conservative design methods and redundant structures which are capable of compensation from a lack of strength in some areas.

It always surprises engineers coming to concrete design and research from other areas such as steel, just how much of concrete design is still done on gut feeling as much as achademic knowledge. Still, at least we have it better than soil engineers, who are doing well if the difference between a predicted and true value for strength is within a factor of 10!

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[vyv_cox]

Re: Like this one, perhaps?

I think your first paragraph is the key. Re-reading what I wrote and reconsidering what I thought I wrote, I never said that composites failed in a ductile manner. My experience is that the reinforcement fibres (mainly glass so far as I am concerned) undoubtedly fail in a brittle mode, again on a micro scale. The matrix, fails either in a ductile manner or the adhesion fails between the matrix and reinforcement. The result is what I described as a progressive failure, a jagged, rough fracture that looks somewhat similar to a ductile fracture in steels. Having witnessed and analysed a good number of hydrostatic over-pressure tests in GRE piping I'm pretty familiar with this mechanism.

The distribution of adhesion/ductile matrix failures is the big problem with more exotic reinforcements such as carbon fibres and Kevlar, because surface tension and other factors lead to less wetting.

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[Twister_Ken]

Pistols at dawn, gents? nm

`

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[vyv_cox]

Re: Pistols at dawn, gents? nm

I don't think it need go that far. Engineers love to argue but it seldom comes to blows!

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[vyv_cox]

Further to my last: Comprehending Engineers.

Comprehending Engineers - Take One
*******************************************
Two engineering students were walking across campus when one said, "Where did you get such a great bike?"
The second engineer replied, "Well, I was walking along yesterday minding my own business when a beautiful woman rode up on this bike. She threw the bike to the ground, took off all her clothes and said, "Take what you want."
The second engineer nodded approvingly, "Good choice; the clothes probably wouldn't have fit."

============================
Comprehending Engineers - Take Two
*******************************************
To the optimist, the glass is half full. To the pessimist, the glass is half-empty. To the engineer, the glass is twice as big as it needs to be.

=========================================
Comprehending Engineers-Take Three
********************************************
A pastor, a doctor and an engineer were waiting one morning for a particularly slow group of golfers.
The engineer fumed, "What's with these guys? We must have been waiting for 15 minutes!" The doctor chimed in, "I don't know, but I've never seen such ineptitude!"
The pastor said, "Hey, here comes the greenskeeper. Let's have a word with him." "Hey George. Say, what's with that group ahead of us? They're rather slow, aren't they?"
The greenskeeper replied, "Oh, yes, that's a group of blind firefighters. They lost their sight saving our clubhouse from a fire last year, so we always let them play for free anytime." The group was silent for a moment.
The pastor said, "That's so sad. I think I will say a special prayer for them tonight. The doctor said, "Good idea. And I'm going to contact my ophthalmologist buddy and see if there's anything he can do for them."
The engineer said, "Why can't these guys play at night?"

======================================
Comprehending Engineers-Take Four
*******************************************
There was an engineer who had an exceptional gift for fixing all things mechanical. After serving his company loyally for over 30 years, he happily retired. Several years later the company contacted him regarding a seemingly impossible problem they were having with one of their multimillion-dollar machines. They had tried everything and everyone else to
get the machine to work but to no avail. In desperation, they called on the retired engineer who had solved so many of their problems in the past.
The engineer reluctantly took the challenge. He spent a day studying the huge machine. At the end of the day, he marked a small "x" in chalk on a particular component of the machine and stated, "This is where your problem is". The part was replaced and the machine worked perfectly again. The company received a bill for $50,000 from the engineer for his service.
They demanded an itemized accounting of his charges.
The engineer responded briefly:
One chalk mark $1
Knowing where to put it $49,999


It was paid in full and the engineer retired again in peace.

===================================
Comprehending Engineers-Take Five
******************************************
What is the difference between Mechanical Engineers and Civil Engineers?
Mechanical Engineers build weapons. Civil Engineers build targets.

=============================================
Comprehending Engineers-Take Six
*****************************************

The graduate with a Science degree asks, "Why does it work?"
The graduate with an Engineering degree asks, "How does it work?"
The graduate with an Accounting degree asks, "How much will it cost?"
The graduate with a Liberal Arts degree asks, "Do you want fries with that?"

=============================================
Comprehending Engineers-Take Seven
*********************************************
"Normal people ... believe that if it ain't broke, don't fix it. Engineers believe that if it ain't broke, it doesn't have enough features yet."
----- Scott Adams, The Dilbert Principle

================================
Comprehending Engineers-Take Eight
******************************************
An architect, an artist and an engineer were discussing whether it was Better to spend time with the wife or a mistress. The architect said he enjoyed time with his wife, building a solid foundation for an enduring relationship. The artist said he enjoyed time with his mistress, because of the passion and mystery he found there.
The engineer said, "I like both." "Both?"
Engineer: "Yeah. If you have a wife and a mistress, they will each assume you are spending time with the other woman, and you can go to the lab and get some work done."

=======================================
Comprehending Engineers - Take Nine
********************************************
An engineer was crossing a road one-day when a frog called out to him and said, "If you kiss me, I'll turn into a beautiful princess". He bent over, picked up the frog and put it in his pocket. The frog spoke Up again and said, "If you kiss me and turn me back into a beautiful
princess, I will stay with you for one week."
The engineer took the frog out of his pocket, smiled at it and returned it to the pocket. The frog then cried out, "If you kiss me and turn me back into a princess, I'll stay with you and do ANYTHING you want."
Again the engineer took the frog out, smiled at it and put it back into his pocket. Finally, the frog asked, "What is the matter? I've told you I'm a beautiful princess that I'll stay with you for a week and do anything you want. Why won't you kiss me?"
The engineer said, "Look I'm an engineer. I don't have time for a girlfriend, but a talking frog, now that's cool."

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