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Old 27-10-2013, 04:17   #211
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Re: Rudder nightmare at sea

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Originally Posted by bfloyd4445 View Post
I too had the same thoughts. My guess is that one of two things happened: was damaged ar some time by being struck above the bearing causing a fracture which went unnoticed allowing water in. Could have happened in backing into a dock etc.. Or poor layup in the factory.

thanks for posting the pictures they have taught us all what to look for when inspecting our boats to see if they are seaworthy or not
Thanks, I hope we will all get some mileage out of this thread. The bottom bearing is situated within the hull rudder housing. If there was a backing into something previously that caused hairline damage not noticeable with the naked eye, it would likely have caused such damage at the point where it snapped off, ie, just as it exits into the water.
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Old 27-10-2013, 04:30   #212
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Re: Rudder nightmare at sea

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Originally Posted by leftbrainstuff View Post
Here's some comments on the problem with using composites for highly loaded safety critical items like your primary means of steering. I've provided them to assist you in being able to understand the technical aspects as you work to get your vessel repaired. Note that I'm not criticising the manufacturer of the yacht.

Some of the comments on the composite failure are interesting. The rudder has obviously been in service for a while so comments about gelcoat and voids is somewhat spurious. I would not be making professional judgements on the actual failure mechanism without careful inspection at both the macro and micro level.

Using a composite post is great for the manufacturer but a less than ideal option for the boat user. Here's why. A composite post is cheap and easy to make and meet the manufacturer's build quality control. Composites have high specific stiffness (stiff and light) but poor abrasion resistance (low hardness) and very low toughness compared to a structural steel option. They make sense for well maintained performance and racing yachts where they are inspected frequently or parts are replaced on a strict schedule.

As an engineer i would consider this design (foam filled composite post) to be non optimum when offshore cruising and as a yacht owner i would consider the design to be insufficiently robust necessitating frequent inspection and / or replacement. A risk based rationale for the manufacturer using this design would likely pass a spreadsheet cost benefit analysis due to the low probability of occurrence. I always demand risk based assessment to include probability, severity and detectability. Often detectability is ignored because it will discount many cheaper options for the manufacturer.

A solid steel rudder post, either heat treated high strength martensitic stainless (4xx series) or a lower strength corrosion resistant alloy such as 316L is tougher than a composite option and therefore will typically fail gracefully giving you feedback that something is wrong. A tubular option could easily meet the strength requirements but also introduces buckling as a failure mechanism. This is why the older blue water yachts typically have a solid rudder post which is way over designed from a static strength perspective.

Note that the primary failure mechanism for a rudder post, that i would use during design will be low cycle fatigue after a high point stress loading from an impact. This is why rudder posts typically didn't fail from an actual impact but generally some time after at a stress loading that can be less than the design stress level. Pros and cons

Option 1 - replace rudder with a manufacturer supplied item
Pros
- Potentially a relatively simple fitment providing no other structural damage
- potentially some form of guarantee although in practice this will be limited and will favour the manufacturer and not you
Cons
- Foam filled composite rudder post will always fail catastrophically and will be not survive any impact.
- a prudent risk based approach will necessitate that you have a secondary rudder

Option 2 - design and fabricate a steel rudder post and bearing mounts
Pros
- design can both functional and survivable by design and material selection
- can build in fail safes rather than just shear off
- can be intentionally designed to fail gracefully
Cons
- your location may not give you access to a competent designer and fabricator
- you will need to ensure the new design doesn't introduce any new emergent problems. The manufacturer may counter that the rudder is designed to be sacrificial to avoid impacting the integrity of the hull during a rudder impact. This is an entirely plausible design decision and is the reason why yachts are classed as either coastal or offshore rated.

Personally, in your current situation cruising offshore, Option 1 plus a secondary rudder is probably the best you can manage. I would place lots of pressure on the manufacturer to support you because their choice of design is a significant factor in your current dilemma and many of their yachts travel the globe. Their reputation is important and it is in their best interests to see you back sailing asap.
Thanks very much for this extensive input, much appreciated. Technical stuff aside, I agree that going with the original and having a secondary is the best option based on our current location. Like all liveaboard yachtsmen, cost will be a deciding factor as to whether we can afford a secondary rudder backup unfortunately.

I am certainly going to try and see if Beneteau would assist us in some way, even if it is only a small way. We will hold thumbs and hope.
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Old 27-10-2013, 04:39   #213
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Re: Rudder nightmare at sea

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Originally Posted by Zanshin View Post
This is typical of this thread - people posting opinions based on stuff that they've read but have actually never tried. This bucket thing, at 3 knots, is absolute b*****t. When I was towed I trailed every single line I had to created drag behind the pivot point of the fin keel. I also had 3 heavy rubber buckets with reinforced handles that each lasted less than 5 minutes before being torn off. Even at lower speeds they would not have lasted much longer.

Remember that having a rudder that is unusable is very different from having no rudder. A broken and locked rudder will keep the boat on a heading, but with no rudder at all a fin keeled boat will swing around, almost 180 degrees (depending upon seas and elasticity of the tow rope and skill of the towboat skipper).
The same applies to balancing sails in order to make way - I've done this numerous times for practice when sailing by locking my wheel and trimming the sails to maintain course. Without a rudder this method will not work, unless perhaps on a lake with no waves and a constant wind of a couple of knots. Certainly not at sea with 2+ meter waves and 15 knots of wind. This is one of the few times where I wished for a skeg or full-keel.

p.s. I've since made up a Jordan Series drogue which should work well as a drag device if I only use a small portion of the cones, should something like that happen to me again.
I completely agree with you re the sails without a rudder. I am surprised that we managed to keep in one direction at 1-2 knots in those conditions. I had the Genoa and main reefed right down and the Genoa somewhere between a hove-to position and a normal position ie, almost in line with the mast. It still every now and then swung 180degrees. Frankly, it was hopeless and only after trying this and sending out the VHF distress signal for a long time with no apparent response, did I activate the EPIRB.

The frustrating thing is that had I waited another 10-15 minutes I would have not had to deploy it because about 10-15min after deployment the fishing boat heard my distress call on the VHF and made way to us. Oh well, another $1000.00 for a new EPIRB.
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Old 27-10-2013, 04:45   #214
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Re: Rudder nightmare at sea

Hi folks, there seems to be a technical problem for me on this thread. I can't get past page 4, any attempt to get further defaults straight back to page 4 and therefore can't read or respond to new posts? Can someone technical advise on what the problem may be?
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Old 27-10-2013, 04:55   #215
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Re: Rudder nightmare at sea

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Hi folks, there seems to be a technical problem for me on this thread. I can't get past page 4, any attempt to get further defaults straight back to page 4 and therefore can't read or respond to new posts? Can someone technical advise on what the problem may be?
I have hit this sometimes. Occasionally restarting helps. Otherwise go to the address for the thread and substitute the page number at the end of the address for the page you want.

I will let Tech Support know
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Old 27-10-2013, 07:07   #216
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Re: Rudder nightmare at sea

Sorry folks, there is a technical glitch on this site and this thread for me. I cant get past page 4. When I am logged in it shows a total of 6 pages but when I log out it show 15 pages in total. When I try and get to the last page it keeps defaulting back to page 4????
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Old 27-10-2013, 07:52   #217
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Re: Rudder nightmare at sea

As most know Hunter Marine suffered several rudder failures after they went to building composite rudder shafts and have since returned to SS. Is Beneteau still using composite shafts?
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Old 27-10-2013, 08:14   #218
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Re: Rudder nightmare at sea

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Originally Posted by robert sailor View Post
As most know Hunter Marine suffered several rudder failures after they went to building composite rudder shafts and have since returned to SS. Is Beneteau still using composite shafts?
Ours is a 2007 model. I would think that they do still use composite.
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Old 27-10-2013, 08:32   #219
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Re: Rudder nightmare at sea

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Originally Posted by bobsadler View Post
Re the query on off-centre emergency rudders: Hydrovane self-steering vanes can act as an emergency ruddy. They can also be installed off-centre (as mine is and it works fine). There are photos on the Hydrovane website illustrating such installations.
Not to mention catamarans can be steered quite well with one rudder mounted 10' or more off-center.

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Old 27-10-2013, 08:36   #220
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Re: Rudder nightmare at sea

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Originally Posted by leftbrainstuff View Post
A solid steel rudder post, either heat treated high strength martensitic stainless (4xx series) or a lower strength corrosion resistant alloy such as 316L is tougher than a composite option and therefore will typically fail gracefully giving you feedback that something is wrong. A tubular option could easily meet the strength requirements but also introduces buckling as a failure mechanism. This is why the older blue water yachts typically have a solid rudder post which is way over designed from a static strength perspective.
Regarding strength of composite vs metal - it seems like this was taken in account with the scantlings because a 5" rudder post on a 50' light mono seems rather large to me. I'm sure that would be a large diameter for that boat if made in solid stainless.

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Old 27-10-2013, 08:39   #221
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Re: Rudder nightmare at sea

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Originally Posted by colemj View Post
Regarding strength of composite vs metal - it seems like this was taken in account with the scantlings because a 5" rudder post on a 50' light mono seems rather large to me. I'm sure that would be a large diameter for that boat if made in solid stainless.

Mark


Sure would! A 5" solid post that size would also weigh a whole lot.
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Old 27-10-2013, 08:44   #222
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Re: Rudder nightmare at sea

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Sure would! A 5" solid post that size would also weigh a whole lot.

and probably still be there with the rudder attached......................
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Old 27-10-2013, 08:51   #223
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Re: Rudder nightmare at sea

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and probably still be there with the rudder attached......................


Oh, yes. Mines 3" solid. Just pulled it, inspected it, rebuilt the rudder, and installed it with new bearings.




5" solid would weigh too much, though. Not an option.
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Old 27-10-2013, 09:03   #224
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Re: Rudder nightmare at sea

Nick Jedi can tell us for sure, but IIRC Dashew uses 5 inch diam heavy wall tube (not sure of the alloy) for his spade rudder stocks, and I've never heard of a failure. Of course, the sample size is way smaller than any of the major production boat lines so that statistic is not very meaningful!

And re the "inevitable" failure of s/s shafts... that depends on the alloy used. Simply going to 2205 improves the odds against crevice corrosion greatly without too great a price hit, and something like Nitronic 50 or one of the super duplex alloys makes it essentially a non-issue. The markedly greater strength of these better alloys means one can go to a smaller section or wall thickness and thus save some weight at the same time.

Cheers,

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Old 27-10-2013, 09:10   #225
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Re: Rudder nightmare at sea

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Nick Jedi can tell us for sure, but IIRC Dashew uses 5 inch diam heavy wall tube (not sure of the alloy) for his spade rudder stocks, and I've never heard of a failure. Of course, the sample size is way smaller than any of the major production boat lines so that statistic is not very meaningful!

And re the "inevitable" failure of s/s shafts... that depends on the alloy used. Simply going to 2205 improves the odds against crevice corrosion greatly without too great a price hit, and something like Nitronic 50 or one of the super duplex alloys makes it essentially a non-issue. The markedly greater strength of these better alloys means one can go to a smaller section or wall thickness and thus save some weight at the same time.

Cheers,

Jim

Tube introduces the possibility of buckling. I realize a bent shaft ain't much better, but at least there's some chance of repairing that.


What about titanium? It's so much cheaper than it was....
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