Elan 333 rudder failures

[vyv_cox]

The news section of the February YM includes a piece on fatigue failures of two Elan 333s, plus a photograph. A representative of the company seems to be blaming 'a machining imperfection present when the rudder stock was first supplied to Elan'. My inspection of the photograph suggests that the fracture is absolutely textbook for the design of the stock, occurring at the lower end of a change of section (which may be what Elan are saying in 'wriggle words').

I have investigated very many fatigue failures (see page 76 of the same issue of YM). Elan suggest that this particular rudder stock had accumulated an unusually high number of cycles, which may well be true. My reading of the design is that this would be categorised as a high stress, low cycle situation, the number of cycles to failure being measured in thousands, rather than tens of millions as would be the case with the more normal design brief of low stress, high cycle. Failure of a stock to the same design is thus inevitable, it is simply a matter of time. Anyone owning one of these boats would be well advised to take up the offer of a replacement at cost price, although if the boat is relatively new I would be pushing for a reduction or free replacement on the grounds that it is unfit for purpose.

 

[doug748]

I think there was a thread on this. The old memory struggles.

The OP had a failure (I seem to recall it was an Elan, could be wrong) that was complicated by the addition of an operating arm for self steering. It seemed to me that the autopilot issue was a red herring and the stock was designed badly. In fact I would go further, it seemed that it was not designed at all, simply turned down with a nominal, or missing, internal fillet rad.

 

[Tranona]

I think there was a thread on this. The old memory struggles.

The OP had a failure (I seem to recall it was an Elan, could be wrong) that was complicated by the addition of an operating arm for self steering. It seemed to me that the autopilot issue was a red herring and the stock was designed badly. In fact I would go further, it seemed that it was not designed at all, simply turned down with a nominal, or missing, internal fillet rad.

Think that was a Hansen called Megawatt. The results of an intensive investigation were inconclusive.

 

[charles_reed]

The news section of the February YM includes a piece on fatigue failures of two Elan 333s, plus a photograph. A representative of the company seems to be blaming 'a machining imperfection present when the rudder stock was first supplied to Elan'. My inspection of the photograph suggests that the fracture is absolutely textbook for the design of the stock, occurring at the lower end of a change of section (which may be what Elan are saying in 'wriggle words').

I have investigated very many fatigue failures (see page 76 of the same issue of YM). Elan suggest that this particular rudder stock had accumulated an unusually high number of cycles, which may well be true. My reading of the design is that this would be categorised as a high stress, low cycle situation, the number of cycles to failure being measured in thousands, rather than tens of millions as would be the case with the more normal design brief of low stress, high cycle. Failure of a stock to the same design is thus inevitable, it is simply a matter of time. Anyone owning one of these boats would be well advised to take up the offer of a replacement at cost price, although if the boat is relatively new I would be pushing for a reduction or free replacement on the grounds that it is unfit for purpose.

So often a failure by a sub-contractor to follow the drawing precisely. It's happened with two keel failures (one reported on the MAIB site), as well as a number of rudder-stock failures.
In the early 80s, working for a UK FLT manufacturer, we had a spate of drive/steer wheels falling off. On a 8 tonne truck, lifting to 35' this could spoil the day. Finally run down to a few forks, where the machinist hadn't radiussed the machined shaft correctly.

 

[photodog]

Surely vyv, if the company is admitting that there was a fault with the product at build, and this fault renders the item NFP, then they should be replacing free of charge under the CPA... In fact they hold liability for up to ten years after the product was put into circulation...

So, frankly I would be pushing for a free replacement all around... It's a clear manufactureing defect which renders the product un safe and NFP... And both ÉLAN and the maker of the rudder stock are liable ...

 

[vyv_cox]

Surely vyv, if the company is admitting that there was a fault with the product at build, and this fault renders the item NFP, then they should be replacing free of charge under the CPA... In fact they hold liability for up to ten years after the product was put into circulation...

So, frankly I would be pushing for a free replacement all around... It's a clear manufactureing defect which renders the product un safe and NFP... And both ÉLAN and the maker of the rudder stock are liable ...

I agree but rather difficult to argue if the boat is several years old. I guess you could use a similar argument for seacocks?

 

[ELAiNe333]

A lot of money to spend, or a wise precaution?

The news section of the February YM includes a piece on fatigue failures of two Elan 333s, plus a photograph. A representative of the company seems to be blaming 'a machining imperfection present when the rudder stock was first supplied to Elan'. My inspection of the photograph suggests that the fracture is absolutely textbook for the design of the stock, occurring at the lower end of a change of section (which may be what Elan are saying in 'wriggle words').

I have investigated very many fatigue failures (see page 76 of the same issue of YM). Elan suggest that this particular rudder stock had accumulated an unusually high number of cycles, which may well be true. My reading of the design is that this would be categorised as a high stress, low cycle situation, the number of cycles to failure being measured in thousands, rather than tens of millions as would be the case with the more normal design brief of low stress, high cycle. Failure of a stock to the same design is thus inevitable, it is simply a matter of time. Anyone owning one of these boats would be well advised to take up the offer of a replacement at cost price, although if the boat is relatively new I would be pushing for a reduction or free replacement on the grounds that it is unfit for purpose.

I did start a thread asking if there was any way I could check the stock on our 333 rudder using non destructive techniques. The consensus seemed to be no but I do wonder if opening up the rudder at the stepped taper would be wortwhile?
If the danger area is exposed would examination reveal the prescence or likelihood of future problem. Ours was one of the last boats built and we sail fairly timidly, a good chance that it will last forever but we will get no guarantee. Same as life really, no guarantee you won't have heart failure tomorrow.
About 500 333s were built and these two are the only instance of failure that have come to light. Yes they were both "Services" boats and will have been used long and hard.
Someone who sailed in the race told us that a Dehler also lost a rudder, any explanation for that one?

 

[vyv_cox]

I remembered that there had been a previous thread, hence my interest.

X-rays would theoretically show up a crack in the stock without removing the surrounding GRP. It would not be an easy task but could well be worth asking a NDT specialist to advise. It would need an isotope to be taken to the boat as presumably removing the rudder would be problematic. Your Yellow Pages should have names to contact. Your profile doesn't say where you are so I cannot suggest anyone.

The next step would be to cut away some GRP and use dye-penetrant but this would probably be rather hit-or-miss. Eddy current might well work if access to each side of the crack site was possible. Ultrasonic probes really need access from a position transverse to a crack, which would be virtually impossible. Other than the dye-pen, again specialist companies are your only option.

No knowledge of the Dehler failure.

 

[robmcg]

Surely vyv, if the company is admitting that there was a fault with the product at build, and this fault renders the item NFP, then they should be replacing free of charge under the CPA... In fact they hold liability for up to ten years after the product was put into circulation...

So, frankly I would be pushing for a free replacement all around... It's a clear manufactureing defect which renders the product un safe and NFP... And both ÉLAN and the maker of the rudder stock are liable ...

I agree with this, but I suppose the get out clause for them would be under 'normal' use, the rudder would be unlikely to fail as the examples of failure quoted imply failure caused at the very upper end of what may be classed as normal use for this type of boat. Potentially difficult one to sort out!

 

[vyv_cox]

I agree with this, but I suppose the get out clause for them would be under 'normal' use, the rudder would be unlikely to fail as the examples of failure quoted imply failure caused at the very upper end of what may be classed as normal use for this type of boat. Potentially difficult one to sort out!

The 'upper end' is only the number of cycles, not (necessarily) the stress levels. Fatigue failure follows a statistical distribution, the two failures have simply seen more cycles than all the others. Ultimately every one will fail, but it might take very many years to accumulate the numbers required.

 

[robmcg]

The 'upper end' is only the number of cycles, not (necessarily) the stress levels. Fatigue failure follows a statistical distribution, the two failures have simply seen more cycles than all the others. Ultimately every one will fail, but it might take very many years to accumulate the numbers required.

Perhaps a reason to question the design parameters of spade rudders in general, considering that people now voyage further for longer with such designs. I would imagine Élan would argue that there is no way to predict the number of cycles that any boat may experience in its working lifetime so don't want to go down the free replacement route. However, I would say, personally, that the potential failure rate is very significant and would at least be a PR disaster for Élan. Lets face it, if you bought an Élan, you are going to want to sail it hard as it is designed as a performance cruiser. If I had one, I would be worried as a rudder failure offshore could be life threatening.

 

[vyv_cox]

Perhaps a reason to question the design parameters of spade rudders in general

Especially the ones with a change of section in the stock just where the maximum bending occurs!

 

[robmcg]

Especially the ones with a change of section in the stock just where the maximum bending occurs!

Quite! Have to question the logic!

 

[30boat]

I'd love to see pictures of this rudder stock.

 

[Yacht Yogi]

I too thought about buying an Elan 333 a little while ago and came across the old post. I contacted the designers, Rob Humphreys at www.humphreysdesign.com and got a reply "Our feeling based on this is that it is worth factoring in a rudder replacement because the cost is so reasonable". They copied me a statement from Elan, which unfortunately did not make clear whether the design has now been improved to eliminate the notch fatigue stress concentration. If not then fitting a new one merely resets the clock rather than eliminating the problem. The problem with fatigue failures is that the stress/life (S/n) curve is logarithmic. That means that a small variation in the sharpness at the base of the step can have a big affect on cycles to failure. So there is the risk that you could be removing and old good one to replace it with a new bad one.

I eventually found that you can buy a J-109 for the asking price of an Elan 333 so I bought one of those instead. Ask key yachting about it but be persistent.

 

[doris]

Someone who sailed in the race told us that a Dehler also lost a rudder, any explanation for that one?

On the Dehler 36 the bottom couple of feet of the rudder were missing. The skipper did own up to having gone around, in reverse, in Poole Harbour. Asking a bit much of a spade rudder to cope with that I imagine. It was easily fixed.

 

[Plevier]

When this happened, wasn't it claimed that the design was for a tapered shaft but to save cost it was made stepped?

 

[JumbleDuck]

My reading of the design is that this would be categorised as a high stress, low cycle situation, the number of cycles to failure being measured in thousands, rather than tens of millions as would be the case with the more normal design brief of low stress, high cycle.

Any chance, do you think, of some high-cycle fatigue from vortex shedding off the rudder? Boats more aggressively sailed might have more weather helm needed, giving higher angles of attack at the rudder and more vortex-shedding. Just a thought. Wouldn't it be nice to see that rudder stock up close?

Meanwhile, perhaps the Elan 333 should be renamed the Rutland Reindeer.

 

[Yacht Yogi]

By aggressively sailed in this context I think you mean badly sailed. Lots of weather helm and lots of rudder angle means lots of drag as you imply by "vortex shedding". This is simply flow separation or stalling. A racing crew is going to trim the mainsail to balance the helm leaving just the proper small amount of weather helm feel. Racing helms are taught to think of the rudder as a handbrake and will politely ask the mainsheet trimmer to adjust as the helm loads up in a gust.

 

[FWB]

Having a transom hung rudder I'm just curious rather than concerned.
This from the freely available YM preview site...

So presumably the metal shaft comes down the rudder with flanges for the glass sheathing and it broke off?