Another Bene with broken rudder bits

[Kenomac]

Sacrificial rudder? What kind of nonsense is that? I think I prefer the model without the sacificial rudder. It would be like like owning a car with a break away steering wheel in case you hit a pothole.

[Jon Eisberg]

Originally Posted by Polux

No, it was not the cleat that sunk the boat but probably a broken hull/rudder on consequence of that. The boat moved back, the rudder went on the chain of the boat behind broke and those were the consequences.

Except that it should not have been like that. A modern Spade rudder (as well as a Skeg rudder) should be designed in a sacrificial way. It should broke and go to the bottom before the force applied to him broke the hull and sunk the boat. It seems to me that is what was starting to happen on that Beneteau, I mean a rudder breaking to save the hull:

The boat was grounded, the rudder was hit and face to the excessive force started to break. It seems to me those supports were designed to be the first thing to break. After that if the force continued the rudder would break at the point the supports were and would fall down, not compromising the hull.

Well, it's one thing to have the bottom portion of a spade rudder designed/constructed to be 'sacrificial' in the event of a grounding or severe impact. The Hunter Passage 420 grounded near Hampton Roads in advance of Hurricane Irene that I pictured in the Avalon/cleat failure thread produced some photographs that showed very clear evidence of Hunter's 'sacrificial' design. The bottom 12-18 inches of the rudder was cleanly snapped off, showing nothing but foam inside the rudder, as the rudder stock obviously terminated above that point... Nothing inherently wrong with such a 'fuse' being designed into such a rudder, particularly on a shoal draft boat, where the difference between the depth of the keel, and that of the rudder, can often be minimal...

However, what failed on this Beneteau was PART OF THE STRUCTURE SUPPORTING THE RUDDER SHAFT INSIDE THE HULL !!! Are you actually suggesting THAT is part of the rudder assembly that should, in effect, be 'Designed to Fail' in the face of a severe impact or excessive force? Seriously? At least, without a watertight bulkhead in place that would isolate that compartment from the rest of the boat?

Isn't that exactly what caused the sinking of the Beneteau BLUE PEARL in the Atlantic last spring? Where the failure of the interior rudder shaft structure inside the boat allowed the unsupported rudder shaft, subject to voilent wave action, to work like a can opener to eventually open up a hole around the rudder bearing in the hull?

Again, it's one thing to have failures or breakages or bending of a rudder outside of the hull... But once structural components begin to fail inside the boat, that's a whole different ballgame... And again, if any builder actually intends for such an assembly to be 'sacrificial', they damn well better isolate that compartment from the rest of the boat with a watertight bulkhead... :-)

Interestingly, a similar failure seems to have been in the process of occurring when Stanley Paris abandoned his second attempt at his solo circumnavigation on KIWI SPIRIT... Sounds like the failure of his mainsail which caused him to bail out into Cape Town may have been a blessing in disguise, he might have easily wound up with a big hole in the back of that boat, if one of his rudders had continued to drop...

I abandoned the solo circumnavigation attempt for the second time because of the mainsail failure. All else was going well, no impediments to further progress, to best of my knowledge. However there was a real problem developing that would also have ended the voyage – read on.

“Just as well you stopped in Cape Town” was the opinion of Mike Giles who is managing the boat repairs and getting her ready for delivery back to the US, after he observed at the dock that the starboard rudder had dropped a couple of inches.. Here is more of what Mike had to say when I asked if I would soon have noticed the problem and what would be the best and worst scenario. . “

“In all likelihood, unless you had a reference on the quadrant height, it would have been hard to pick up. When I saw it had fallen, the fix included removing the life raft, opening up the locker, removing the cover plate. Then attaching a lashing and connecting it to the main halyard through a “guide bridal” to get the angle correct. You would have been able to do that at sea i guess, but would have required the main halyard for the task. …….

The above is best case. If it went any further, the rudder would more than likely dislodged from the top bearing and would thus have no support, so you would have had a rudder floating around, probably causing damage and left with a gaping hole.The tie bar and quadrant would have been damaged.

You would have had to disconnected the tie bar, connect up the port wheel and continue.If any structural damage, that would have definitely be the end of your trip.Fixing holes under the hull would not have been easy.

Worst case a long limp back to land with a hole in the boat. Your safety would have been the water tight trap door behind the aft birth.So there was a design for the worst case… Like I mentioned earlier, lucky you ended up in Cape Town. I think you had some lucky stars looking out for you.” Mike Giles

So I suspect regardless of the sail issue the trip would have had to be abandoned at some later point and with the boat in a much more dangerous condition – life threatening hull damage leading to a possible sinking though it was in a water tight bulkhead. Ironic to state that “…I think you had some lucky stars looking out for you.”

http://stanleyparis.com/?p=1787

[a64pilot]

Originally Posted by Kenomac

Sacrificial rudder? What kind of nonsense is that? I think I prefer the model without the sacificial rudder. It would be like like owning a car with a break away steering wheel in case you hit a pothole.

No,
I have to agree that designing a mechanical system to fail in a controlled manner assuming of course that design loads have been exceeded is logical.
I bet on most older, well respected stronger designs if you apply enough force to the rudder to where something fails, the rudder will fail before the hull, and I think that is all he is saying. Of course you can't design against every possible occurence


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[TeddyDiver]

In Turkey there's no tide to talk about. I think the biggest difference btw low and high tide is around 0.3m / 1'. Much more one can expect from changing weather or just from a by passing ship.
The original stucture supporting the rudder is weak and this was not the first one failing..

[Kenomac]

Originally Posted by a64pilot

No,
I have to agree that designing a mechanical system to fail in a controlled manner assuming of course that design loads have been exceeded is logical.
I bet on most older, well respected stronger designs if you apply enough force to the rudder to where something fails, the rudder will fail before the hull, and I think that is all he is saying. Of course you can't design against every possible occurence

I hadn't thought of it your way, which is correct. I thought Polux was referring to the rudder shaft breaking away inside the hull like in the couple's video. Having the tip break off under excessive loads like you suggest is a good idea.

[robert sailor]

Yes having a sacrificial portion on the lower rudder does make sense because you can loose this and still have steerage but the structure holding the rudder in place should be bullet proof and of course there lies the problem as it doesn't appear to have been.

I have my bias's and each of them has come through personal experience not what I read on forums. I sailed offshore 30 years ago in a C&C 36 and after a very rough sail 150 miles off the Wa/Or coast the top of the rudder post was loose in the bearing and had made the hole into an egg shape. I pulled the boat and had new bearings installed and the people at the yard also suggested that they beef up the support structure a bit as they considered it light duty. After sailing south and then over to Hawaii on the return trip to Canada the damn rudder was loose again and making noise each time we rolled. It really bothered me and I had a hell of a time sleeping worrying about it. I climbed into the back and over tightened the steering lines and it did quiet it down but I knew all I had done was put more load on the bottom bearing. I got us home but on return I had the whole area all redone again and I wrote off any future offshore cruising with a lightly built spade rudder. If they are built well and the support structures are built well they are just fine but in my experience in many of these entry level boats I don't see that as of course it cost money.

[CaptNemoO2]

Originally Posted by Kenomac

Sacrificial rudder? What kind of nonsense is that? I think I prefer the model without the sacificial rudder. It would be like like owning a car with a break away steering wheel in case you hit a pothole.

Well, not as minor as a pothole, but all modern cars have a collapsing steering column due to adding crumble zones. Both features are engineered failure points designed to protect the occupants. Would I want a rudder fall off? No, but if I had to choose a rudder falling off or the hull breaking and sinking the boat, I would pick the rudder everyday. There is the possibility of something being too strong or too stiff, which can transfer loads or vibrations to another point that wasn't intended to receive them. The problem with boats is destructive testing is usually never done. So even doing analysis, if that is even done, the engineer is making major assumptions on the forces involved.

However, the rudder support structure inside the boat should never be the weak point. Ideally, the weak point would be outside the hull, where a total failure would leave the rudder post in the hull to maintain a water seal. In the case of the Blue Pearl, the structure was the weak point. That video showing the rudder post flopping around was terrifying. When the structure failed, the too strong of a rudder ripped the hull open.

On my friends Hunter, his weak point was the plasticity of the post. Coming into Great Salt Pond, Block Island for the first time, he arrived in the morning fog and ended up on the wrong side of the jetty. A wave pushed him up an onto the jetty but he was able to bounce off. He dropped anchor and waited for a tow, which then tied him up to my father's boat. When I dove under his boat, his rudder was bent about 20°, causing the rudder to hit the hull when trying to turn. I put a line to the end of the rudder that went back to the primary winch on my dad's boat and we straightened the rudder enough to be able to steer. He made it all the way to Old Lyme, CT before he started taking on water from the prop strut. That too got dinged in the ordeal, and after motoring, the vibrations from being misaligned worked the screws loose. Had ther been wind, he would have been able to make it anywhere.

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[letsgetsailing3]

Originally Posted by TeddyDiver

In Turkey there's no tide to talk about. I think the biggest difference btw low and high tide is around 0.3m / 1'. Much more one can expect from changing weather or just from a by passing ship.
The original stucture supporting the rudder is weak and this was not the first one failing..

Then they must have anchored their boat at less than 1' depth. We also don't know for sure that the damage wasn't from some previous incident.

I'm saying there are a lot of people bashing the boat brand, when they don't know as much as they claim about the history of the boat.

[neilpride]

Originally Posted by Kenomac

Sacrificial rudder? What kind of nonsense is that? I think I prefer the model without the sacificial rudder. It would be like like owning a car with a break away steering wheel in case you hit a pothole.

Sacrificial make sense, i rebuild a couple of rudders that way, in a collision event the bottom of the rudder go leaving the top operational in some way ...

[Kenomac]

Originally Posted by neilpride

Sacrificial make sense, i rebuild a couple of rudders that way, in a collision event the bottom of the rudder go leaving the top operational in some way ...

Neil,

Please read post #51, I agree with you.

[neilpride]

Yah, i see it later, thats cool, Np..

[Polux]

Originally Posted by robert sailor

When you look at the interior structure for the rudder don't you get the feeling that it is on the light side?

It seems that the one on the Hunter was too strong since it did not break in a way that would prevent boat flooding (damaged hull?)

The design of a sacrificial rudder is a complex one and the forces have to be carefully measured to design a system that would break in a clean and not harmful way before causing hull breakage and the boat to sunk. I don't have the data to tell you if it was well designed or not but those apparent fragile supports seem to be on the right place to be the first thing to fail, provoking the breakage of the rudder on that place that seems to me is the best place to limit damage to the hull integrity.

[TeddyDiver]

Originally Posted by letsgetsailing3

Then they must have anchored their boat at less than 1' depth.

Not necessarily, low and high fronts with considerable difference in the air pressure can cause several feet of water level change locally. Same goes with dredged shipping lines close to shore.

[letsgetsailing3]

Originally Posted by TeddyDiver

Not necessarily, low and high fronts with considerable difference in the air pressure can cause several feet of water level change locally. Same goes with dredged shipping lines close to shore.

Ummm, what? You really can't have it both ways. Which is my point. You don't know what happened, or the history of that rudder.

[Polux]

Originally Posted by Kenomac

Sacrificial rudder? What kind of nonsense is that? I think I prefer the model without the sacificial rudder. It would be like like owning a car with a break away steering wheel in case you hit a pothole.

Has it was told by someone the cars in fact have a collapsible steering colon and his common knowledge that rudders and skegs on a well designed boat are sacrificial and not only the point of them as says Jon. The problem here is that the force generated on a rudder, amplified by the arm (its length) when it is subject to a high speed collision with an heavy object (a container for example) if the rudder is not a sacrificial one can lead to a loss of hull integrity resulting on the sinking of the boat.

To make a rudder (or a skeg) strong enough not to fail on normal circumstances, but able to break away cleanly if subject to a force that can lead it to damage the hull, is a very difficult design task , one that can only be done with knowledge of the materials, the involved forces on a computer simulated situation. Only after that it is possible to design a rudder and rudder system able to respond to those two contradictory situations in what regards strength.

It isobvious that it does not work every-time, like on the case of the Blue Pearl or on the case of that Hunter, but it has worked out on the many cases of boats that had lost the rudder after having hit submerged heavy objects without having compromising hull integrity.