Rudder Drop Off

[ELAiNe333]

No, not new here, but taken on a new persona.
During the summer YM featured two ELAN 333s that had lost their rudders having sheared the stainless stock (right word?) where it was step tapered within the rudder moulding.
I would apprecciate the old salts forgetting out their hobbyhorse about spade rudders and instead consider whether there is a practical method of non destructive testing to check for cracks or fatigue. I feel this might be a comfort not just for 333 sailors but for many with spade rudders.
Lowering the rudder on a 333 is relatively easily accomplished so taking it away for testing might well be worthwhile.
Is Xray or ultrasonic or anything going to be give an answer?
Particularly keen to hear from others with the same concern as a testing house might be more amenable to setting something up if there was a prospect of several customers.

 

[johnphilip]

What are the odds?

Over 400 of these built and I have heard of no other problems, similar odds to many other mishaps? A good question though, probably applies to all spade rudders to some degree.

 

[sailorman]

we have a spade rudder & 18 months ago i dropped it to visually inspect the s/s stock. pleased all was ok.

 

[neil_s]

Not the same sort of rudder, but I have a test that gets applied to mine every couple of years. I lock the rudder with a couple of pieces of 3x2 bolted together through the propellor arch and apply a fixed load at the end of the tiller. I do it for both directions. This is designed to test the integrity of the welded tangs buried in the rudder moulding. Perhaps you could contrive a similar 'proof' test for your spade?

Neil

 

[Tranona]

Sure there will be some way of crack testing as this is commonly done on, for example suspension components on racing cars. However, from the reports that I have seen the failures did not seem connected with existing cracks, so not sure what it is going to tell you.

As already suggested there are hundreds of that particular design in use and literally thousands of similar designs with very few failures.

You might contact Rob Humphries (the designer) as he was investigating the failures.

 

[ELAiNe333]

Buried problem

we have a spade rudder & 18 months ago i dropped it to visually inspect the s/s stock. pleased all was ok.

Unfortunately the problem with these rudders was at the step taper of the stock about a foot into the top of the fibreglass,just below the top tang which transmits the steering torque to the blade. hence the need for x-ray or similar.

 

[ELAiNe333]

Maybe

Not the same sort of rudder, but I have a test that gets applied to mine every couple of years. I lock the rudder with a couple of pieces of 3x2 bolted together through the propellor arch and apply a fixed load at the end of the tiller. I do it for both directions. This is designed to test the integrity of the welded tangs buried in the rudder moulding. Perhaps you could contrive a similar 'proof' test for your spade?

Neil

Quite difficult to know how much load to apply to detect a problem but not cause damage. Your clamp holding the rudder would need to be fairly low down as the top tang remained in place on the top part of the stock.
If I could detect the next tang down the blade with a DIY type pipe detector I suppose that would be the point to hold the rudder rigid for your test. I am not sure it is the full answer to restore confidence.

 

[lenseman]

No, not new here, but taken on a new persona.
During the summer YM featured two ELAN 333s that had lost their rudders having sheared the stainless stock (right word?) where it was step tapered within the rudder moulding.
I would apprecciate the old salts forgetting out their hobbyhorse about spade rudders and instead consider whether there is a practical method of non destructive testing to check for cracks or fatigue. I feel this might be a comfort not just for 333 sailors but for many with spade rudders.
Lowering the rudder on a 333 is relatively easily accomplished so taking it away for testing might well be worthwhile.
Is Xray or ultrasonic or anything going to be give an answer?
Particularly keen to hear from others with the same concern as a testing house might be more amenable to setting something up if there was a prospect of several customers.

Hiya - welcome to the forums under your new persona.

These incidents to which you refer, do you know 'exactly' what happened to cause the problems?

The reason I ask is that if the yacht tucked its bow into a deep sea and the stern was lifted clear and them broached, the resultant forces on the rudder and associated components as the yacht slams back into the water having broached, could easily rip off a rudder.

It happened to a forum members yacht north of New Zealand three years ago:

http://www.ybw.com/forums/showthread.php?t=217968

What I am trying to point out, it might not be due to poor or weak design but just the forces of nature acting on a rudder in an unnatural way?

.

 

[AndrewB]

You say that the rudder is easily dropped to enable the stock to be inspected. I think this is a large part of the answer. Give the stock an annual inspection. Hidden in a bearing where it gets very little oxygen, crevice corrosion starts from the surface of the metal. I've seen several stainless stocks to which this has happened. Eventually the stock becomes wasted and will give way close to the point where it enters the bearing.

So, any surface indication of crevices - change at once. I bet the ones that failed hadn't been inspected in years.

 

[Bobobolinsky]

Dye penetrant inspection is a cheap and easy method, get the three aerosols from any welding supplies place

http://www.ebay.co.uk/itm/SWP-WELD-...520?pt=LH_DefaultDomain_3&hash=item416c2f1e50

You need cleaner and developer in addition

There are lots of instruction on the web.

If there is an abrupt section change, you may have to polish the root of the section change with emery cloth, or the dye will give you a false reading.....and a heart attack

 

[estarzinger]

The OP is saying that the 'weak point' is buried inside the rudder, so no visual/dye exam is going to help . . . unless you take remove sections of the rudder skin, which I have in fact done on suspect rudders to be able to inspect the welds . . . but it creates a mess to repair if the stock is in fact ok.

x-ray or ultrasound are the only non-destructive options. They 'might' detect a hairline crack, but they might not. They will not detect a stress riser 'design weaknesses' (what lenseman is suggesting above).

There might be an electrical conductive test that would identify major cracks (less resistance = solid shaft, more resistance=crack). This is used in some structural situations. But you need to get a baseline of data so you know what is a good measurement vs a bad measurement and to do that you would been several good and bad rudders (of the exact same design/construction) which you may not have access to. Again this will not identify the stress riser sort of weakness.

Sorry, but I don't think there is a good satisfying solution.

 

[charles_reed]

Having once had a rudder blade break, I'm aware of the disconsolation it can cause.

I doubt, in view of the construction of the part that anything that can be done in the way of effective testing.
Many years ago I was in charge of selling a vast, 3-wheeler narrow aisle fork-lift truck. Being simpler, cheaper and more effective it soon took a large market share and all was well until several started to shed their steering and motor-in-wheel unit.
All the units had fatigue-fractured at the same point where the machining stopped and there was a sharp angle.
Add to that well-known-to-design engineers foible of machined parts, the use of 316 stainless with its penchant for work-hardening and crystallisation and one has an almost-inevitable result with all Elan 333's after a measurable period of use.
Perhaps owners have a case for damages against Elan, but the only way of preventing the problem is to replace all the rudder shafts with ones without a step, and instead have a radiussed curve (it certainly solved the problem with the Bison).

PS The problem of fatigue at corners has been amply documented since the mid-50s - the notorious one lead to the re-design of the de Havilland Comet windows.

 

[wotayottie]

Is Xray or ultrasonic or anything going to be give an answer?

You could x ray to check for cracks but if the failure point is within the moulding you could not use ultrasonics. Neither will detect fatigue.

It might be more practical to make sure you have some sort of emergency rudder on board. Even better would be to recognise that a problem exists and prevent it. Take the rudder off the boat, cut it with an angle grinder along the edge and split the tow halves. Strengthen the stock and then re bond the rudder. Its likely to be much less expensive that a replace after failure, much less dangerous and would give peace of mind. It would even help the resale value of the boat. And it would be an easy winter DIY.

 

[vyv_cox]

I looked at the photos of the fractures in YM and it appeared to me that they had occurred at a change of section and for that reason were characteristic of fatigue. Fatigue has nothing to do with 'work hardening' nor 'crystallisation', it is simply the result of a combination of stress above a certain value and cycles. A crack grows, typically from a stress raiser such as a change in section, keyway, corrosion pit and many others. The crack is normally unseen until the remaining metal in the cross section is unable to sustain the load applied to it and the component breaks. For this reason fatigue fractures are described by their witnesses as 'sudden, without warning', whereas in fact the crack may have been growing for months or even years. There is a page on fatigue on my website here.

Dye penetrant is the only test I can think of that could be used by an owner. It requires access to the suspect section change. Specialist companies can offer further NDT examinations but all will be difficult for a rudder stock. Ultrasonic testing is not applicable through GRP as far as I know, it always requires a skilled operator and can be quite subjective. X-ray is a possibility, although not easy on this component, and the rudder would have to be taken to an NDT shop to have it done. Again, a transverse crack may not be very easy to see. I have used a technique that is useful for detecting surface cracks but it relies on passing an electrical current through the metal, so again full access is required.

 

[ELAiNe333]

Slight misunderstanding

You say that the rudder is easily dropped to enable the stock to be inspected. I think this is a large part of the answer. Give the stock an annual inspection. Hidden in a bearing where it gets very little oxygen, crevice corrosion starts from the surface of the metal. I've seen several stainless stocks to which this has happened. Eventually the stock becomes wasted and will give way close to the point where it enters the bearing.

So, any surface indication of crevices - change at once. I bet the ones that failed hadn't been inspected in years.

Sorry but visual inspection is not going to help as the fracture is within the rudder blade, not above it.

 

[William_H]

Non destructive testing

The primary NDT method applicable for this shaft would be mark 1 eyeball with magnifying glass. Or possibly by dye penetrant testing. However a better method would be the eddy current method. This is like a tiny metal detector that detects not metal but rather gaps in the metal which give high electrical resistance. Even the tightest cracks can be detected this way. Used for alloy aircraft wheels looking for cracks around the rim. (among other things)
All these methods of course require opening up the rudder. In which case you might as well replace the shaft with a better design.
Radiography (Xray) is often touted for testing inaccessible components. It is however not very practical for this application. Radiography requires a really open gap before it can be detected. great for broken bones which do separate but no good for the tiny cracks around the shaft that might be there before it lets go.
So replace the shaft if you are worried. Or how about setting up an emergency rudder system. A transom rudder can be very effective it can be designed a bit like an over sized dinghy rudder and stowed away in case of rudder loss. good luck olewill

 

[ELAiNe333]

Step Fatigue

I looked at the photos of the fractures in YM and it appeared to me that they had occurred at a change of section and for that reason were characteristic of fatigue. Fatigue has nothing to do with 'work hardening' nor 'crystallisation', it is simply the result of a combination of stress above a certain value and cycles. A crack grows, typically from a stress raiser such as a change in section, keyway, corrosion pit and many others. The crack is normally unseen until the remaining metal in the cross section is unable to sustain the load applied to it and the component breaks. For this reason fatigue fractures are described by their witnesses as 'sudden, without warning', whereas in fact the crack may have been growing for months or even years. There is a page on fatigue on my website here.

Dye penetrant is the only test I can think of that could be used by an owner. It requires access to the suspect section change. Specialist companies can offer further NDT examinations but all will be difficult for a rudder stock. Ultrasonic testing is not applicable through GRP as far as I know, it always requires a skilled operator and can be quite subjective. X-ray is a possibility, although not easy on this component, and the rudder would have to be taken to an NDT shop to have it done. Again, a transverse crack may not be very easy to see. I have used a technique that is useful for detecting surface cracks but it relies on passing an electrical current through the metal, so again full access is required.

Thank-you Vyv, the example on your site of the failed drive shaft looks a very similar situation to the 333 rudder stock. I had been wondering if the stocks on the two failed boats might have had well advanced fatigue cracking or even completly broken with the GRP holding the rudder together until they hit the heavy weather. Might it be more easily detected if the cracking is well advanced? It might be worth an exploratory cutting into the blade to check?

 

[oldsaltoz]

I'm still trying to work out why anyone would would put a step in a rudder stock between tangs in the first place ???

What on earth was this design supposed to achieve ???

Why a step and not a taper ???

I have worked on many rudders over the years and seen some pretty odd designs but I suspect this one may just take the cake.

Good luck and fair winds to all.

 

[ELAiNe333]

X-ray hindsight

I'm still trying to work out why anyone would would put a step in a rudder stock between tangs in the first place ???

What on earth was this design supposed to achieve ???

Why a step and not a taper ???

I have worked on many rudders over the years and seen some pretty odd designs but I suspect this one may just take the cake.

Good luck and fair winds to all.

I agree that the step down in stock thickness should be tapered but I suspect that the builders could not believe that a reduction in section of such a heavy (about 50mm) bar could have this consequence. The section has to reduce or the rudder thickness would have to be considerably thickened in the lower half. As an owner I did not have the opportunity to be aware of this build detail. Sharp changes of section are poor practice.

 

[vyv_cox]

Thank-you Vyv, the example on your site of the failed drive shaft looks a very similar situation to the 333 rudder stock. I had been wondering if the stocks on the two failed boats might have had well advanced fatigue cracking or even completly broken with the GRP holding the rudder together until they hit the heavy weather. Might it be more easily detected if the cracking is well advanced? It might be worth an exploratory cutting into the blade to check?

Is there a radius at the root of the change in section? If not this is a classic case of fatigue in shafts. When I worked at the refinery I once had seven of them on my desk in one week!

I don't think there is any reliable test that will tell you if there is a crack without cutting the GRP away. I doubt very much that the GRP itself was holding the blade on, the YM article sounded to me like a typical fatigue failure. It will be a single crack right in the corner. Can be quite difficult to detect a crack there, even with dye penetrant.

This is how it looks on a hollow compressor piston but that is on a flat face. In a sharp corner the dye tends to remain there when it has nominally been washed off. Heaving on the blade tip might help visibility if there is a crack there.