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Old 30-10-2014, 21:33   #121
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Re: Rudder Failures

Guys, I get it when it come to the strengths of adhesives.
Prior to composite crash tubs in race cars. The ones which protect the driver when he nails the wall doing 220mph. They used to make the crash tubs out of aluminum, glued together with epoxy. Yeah.
And I've watched them spin the nuts off of the keel bolts of boat suspended in Travel Lifts, only to have the keels not drop off, because the builder used 3M 5200 as the bedding agent.

That said, there are some things I'm just not up for explaining via text, like proper bulkhead installation.
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Old 30-10-2014, 21:34   #122
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Re: Rudder Failures

Polux, do you work for, in any way, any boat manufacturer?
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Old 30-10-2014, 21:37   #123
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Re: Rudder Failures

Quote:
Originally Posted by colemj View Post
Much of what you describe is substandard, but this one is normal. A usual AP tiller arm is 10" and located close to the top bearing. I know of very few that are not like this. In fact, most drive units would not work with a longer lever arm - either not being able to turn the rudder enough, or taking too long to turn it. Likewise, most rudder posts end shortly above their top bearing (hence the term "top"), so there really isn't much space above that for a quadrant and tiller arm.

Also, Plexus is generally stronger than any fillet of resin/filler. It is quite remarkable in its qualities and I don't have any issues with much of a boat being glued with it at all. Of course, where fibers are necessary for load reasons, it is not applicable.

Mark
Yeah, i see this short lever arms before, but what happen when you fit the arm to a short Post from lower bearing to top bearing ? in good weather nothing i guess , things are diferent in my eyes if you get caught in bad weather , i see it before in a Lagoon 380 delivery ,,,surfing waves the AP work hard to counteract the tendency of broaching and even sometimes stop working at all and swichting to standby, i understand now why some Lagoons need to replace the top bearing after few years of sailing, the ram push sideways the rudder stock in strong conditions, when i say surfing waves i say nothing out of the reality, 25 to 30 knts and 8 to 10 ft waves...

Early beneteau models are diferent regarding the stock AP arm, take for example the 50, not the oceanis versión, by far the AP arm is longer and robust and the top rudder stock rest in the deck sideways with a delrin bearing....
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Old 31-10-2014, 01:09   #124
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Re: Rudder Failures

One issue I don't think has been mentioned yet is weather helm and other forms of rudder abuse.

Saw a Bavaria loose its rudder once. Sailing alongside them it was obvious they hand serious weather helm in 25 knots but they didn't realize and sure enough 15 minutes later their rudder snapped off.

The Bavaria was on its first 4 hours of a month cruise across the Coral Sea. Sure Bavaria rudders are probably not the toughest and it should have been checked....

In this case I think the rudder probably broke because the people didn't know how to sail more so than design or maintenance.

The crew, three navy guys in late 50s limped back to Cairns on a drogue and got a tow into port. Think they were trying to race us.
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Old 31-10-2014, 02:48   #125
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Re: Rudder Failures

Don't take this personally as I know you are probably a decent sailor but no amount of rudder helm should cause a rudder to fail. If it failed in the conditions you described then it was just under designed/built.
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Old 31-10-2014, 05:26   #126
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Re: Rudder Failures

Hmmm.

Interestingly, I can quote at least 6 dramatic rudder failures over last couple of months.

I must be extremely well informed then!

b.
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Old 31-10-2014, 05:32   #127
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Re: Rudder Failures

One of the things we don't really know about rudder failures (or keel failures) is any earlier damage to them from hitting "stuff". Sure sometimes we know but I bet most of the time that is kept secret.

Afterall how many people really are stupid enough that when their rudder fails and they are asked if they had hit a rock with it in the past would say yes to that. But I bet the insurance company asks and hopes.
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Old 31-10-2014, 05:41   #128
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Rudder Failures

Some posts have mentioned the length of the tiller arm where the autopilot drive is connected to the rudder. What difference is there to the length of this arm in regards to rudder forces? It seems that the torque the rudder applies to the post would be about the same no matter the length of this arm. The force required by the drive would be more for a shorter tiller radius but the travel is less so net power should be about the same.

Similarly, at least on our boat I think the wheel can apply way more rudder post torque than the autopilot. I don't see why autopilot use has any bearing on why rudders fail. Can anyone explain the theory on that?
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Old 31-10-2014, 05:45   #129
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Re: Rudder Failures

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I don't see why autopilot use has any bearing on why rudders fail. Can anyone explain the theory on that?
It is because unlike when hand steering the AP has no "feel" of whether it should keep trying to turn the rudder. It only cares about maintaining course no matter how hard it has to turn the rudder to do so.
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Old 31-10-2014, 05:57   #130
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Re: Rudder Failures

I still don't see why that is relevant to rudder failure. Any rudder should be strong enough to be dragged through the water at any angle or speed. If not I don't see why it's the AP's fault.
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Old 31-10-2014, 05:57   #131
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Re: Rudder Failures

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Originally Posted by sailorboy1 View Post
It is because unlike when hand steering the AP has no "feel" of whether it should keep trying to turn the rudder. It only cares about maintaining course no matter how hard it has to turn the rudder to do so.
The AP driving hydraulics driving the rudder has the same amount of "feel"
(feedback been the correct term) as the helmsman driving the hydraulics.......Zero....
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Old 31-10-2014, 06:00   #132
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Re: Rudder Failures

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Originally Posted by barnakiel View Post
Hmmm.

Interestingly, I can quote at least 6 dramatic rudder failures over last couple of months.

I must be extremely well informed then!

b.
All of us that are out there sailing run into failed rudders, friends or friends of friends. It is in fact quite common compared to other failures. We keep hearing about ARC boats but most of them are new or newer and while they have failures I don't think its a good measuring stick because its such a small sample and they are sailing the easiest routes across the Atlantic.
We ran into a Hunter in the South Pacific that was on its 3rd rudder ( not knocking them as it could have been any one of the production boats) We were sailing a CS36T at the time and when we hauled in NZ the rudder had a hairline crack running around the outside joint (built in 2 halves) and it would have failed given enough time. Later I started to understand that it was like many rudders water logged and during the winter it had frozen and that started the process.We like to make ourselves feel better by suggesting that the rudder had been damaged and I guess it was but not from hitting anything, by not being built tough enough to begin with. Personally I think most rudder failures are just that, poorly built, or built for purposes intended, whatever.
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Old 31-10-2014, 06:10   #133
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Re: Rudder Failures

Quote:
Originally Posted by neilpride View Post
Yeah, i see this short lever arms before, but what happen when you fit the arm to a short Post from lower bearing to top bearing ? in good weather nothing i guess , things are diferent in my eyes if you get caught in bad weather , i see it before in a Lagoon 380 delivery ,,,surfing waves the AP work hard to counteract the tendency of broaching and even sometimes stop working at all and swichting to standby, i understand now why some Lagoons need to replace the top bearing after few years of sailing, the ram push sideways the rudder stock in strong conditions, when i say surfing waves i say nothing out of the reality, 25 to 30 knts and 8 to 10 ft waves...

Early beneteau models are diferent regarding the stock AP arm, take for example the 50, not the oceanis versión, by far the AP arm is longer and robust and the top rudder stock rest in the deck sideways with a delrin bearing....
Lagoons, like many catamarans, have their rudders connected by a beam connected to the rudder posts with a short tiller arm like used in most autopilots. This is normal for catamarans and does not impact the steering system or bearings at all.

Most cats with cross-tie systems mount the AP drive unit directly to the cross bar (which is connected to the rudders with short tiller arms). I believe the L380 is this way.

Edson doesn't even sell a tiller arm for autopilots longer than ~12". Having fairly recently researched various autopilot systems, I found no linear drives that could be mounted using a tiller arm longer than 12" unless the rudder stops were set at a ridiculously small angle - they do not have the throw length for any longer.

Our boat has a pull-pull cable steering system with quadrants not too much longer than the short AP tiller arm. The distance between top and bottom bearings in the rudder tube is ~20-30". With pull-pull systems, at least one rudder always has a side load turning force. After 16yrs, with many AP miles in conditions you describe and worse, our bearings are fine and our AP has never stalled out or turned itself off.

You are barking up the wrong tree with this "short tiller arm" thing.

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Old 31-10-2014, 06:16   #134
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Re: Rudder Failures

Quote:
Originally Posted by IslandHopper View Post
The AP driving hydraulics driving the rudder has the same amount of "feel"
(feedback been the correct term) as the helmsman driving the hydraulics.......Zero....
For an in-line hydraulic system this may be true. However, for a non-hydraulic, or hydraulic linear drive, many AP's get feedback from the amount of current they need to supply to move the drive a certain amount at a certain speed. They use this feedback to adjust how they operate the drive and steer the boat, and some units can/do have alarms when drive force becomes high.

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Old 31-10-2014, 06:33   #135
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Re: Rudder Failures

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Originally Posted by IslandHopper View Post
The AP driving hydraulics driving the rudder has the same amount of "feel"
(feedback been the correct term) as the helmsman driving the hydraulics.......Zero....
Maybe if it goes on long enough that AP "Brain" will learn, but in my experience it starts off pretty stupid and with a sudden following wave will just try to turn regardless (at least my rotary electrical drive unit will)
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