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Old 08-12-2008
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Question Steering Failure after Sailing

Hi Everyone:

I had an interesting event occur last Sunday while out sailing my Pacific Seacraft Orion 27 in San Diego harbor. We had very good wind, and were able to get up to 5.5 knots sustained speed most of the day. There were a lot of boats out, so we did get tossed around some by wakes, etc. but nothing I would consider abnormal, or unexpected of being out on the water. While motoring back into the marina, my hydraulic steering system failed, and for a few brief minutes was left drifting into the marina until I was able to rig the emergency tiller and regain control. Very scary at first, since we were about 4 boat lengths away from either running into other tied up boats, or hitting the waste pump out dock, depending on the direction of the rudder when the steering failed. I used the motor and a combination of forward and reverse to avoid hitting anything while my wife dug out the emergency tiller and then I got it installed on the rudder post. Luckily disaster was averted, but now I need to figure out why the steering failed and what to do about it.

Some History:

Last year about May, I had a local Marine Service company replace my worn out 27 year old rack and cable steering system with a new semi custom hydraulic system. Since my steering pedistal is mounted on my hinged engine access cover, a normal wire cable system can't be fitted, since when opening up the engine cover, the entire pedistal rotates with the hinged cover, and the hydraulic system looked like the way to go. I also couldn't find a replacement rack and cable system on the market heavy duty enough for my boat.

I had heavy duty Marine grade parts, pumps, hoses, etc. sized for the boat, and some custom mounting hardware made up, and powder coated to resist corrosion. All worked well for a little over a year. After getting back to the slip safely, I opened up the engine cover and saw that the connection from the hydraulic ram to the swivel fitting on the tiller arm were separated. This is a threaded connection. Not sure yet if they became unscrewed, stripped out, or if the swivel fitting simply broke / sheered.

The guy who designed the system is a 20+ year experienced Mechanical Engineer who has been doing Marine work for a very long time. He came highly recommended, and did a awesome design job. What I need to figure out is if this is just a random component failure (infant mortality) or a bad design or part selection issue. Not sure how to determine if the forces on the rudder during normal sailing were more than the fitting could handle, or if alignment might be to blame, etc.

Any thoughts on where to start the investigation, or what questions to ask the Engineer after he comes and takes a look at the problem? I am a Electrical Engineer by trade, but this mechanical linkage / force, strain stuff is a little out of my area of expertise, but I understand how to troubleshoot when I have a little background information. I would appreciate any feedback or suggestions on how to make sure this doesn't happen again, especially when offshore, and how I can guarantee a sturdy steering system.
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LittleWingCA
1980 Pacific Seacraft Orion 27
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Old 08-12-2008
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You ask ;
"Any thoughts on where to start the investigation, or what questions to ask the Engineer after he comes and takes a look at the problem?
I would think you would want to start;
"the connection from the hydraulic ram to the swivel fitting on the tiller arm were separated."

I am having a hard time picturing "the connection". Is it a threaded nipple that is screwed into the hydraulic swivel?
Did it break at the threads?
Could you post a picture?
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Old 08-12-2008
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well, sounds to me like you already know what the problem is - your ram got disconnected from the tiller arm.
On my boat this connection is a fork on a ram that fits over tiller arm, and is connected with a beefy clevis-type pin (about 1/2" diameter, I reckon).

Actual hydraulic steering failures would probably be slower to develop (unless a hose or connector fails catastrophically and all the fluid leaks out). Otherwise, slow leaks would make system feel spongy and unresponsive for a while before it gives up completely.
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Quote:
Originally Posted by brak View Post
well, sounds to me like you already know what the problem is - your ram got disconnected from the tiller arm.
On my boat this connection is a fork on a ram that fits over tiller arm, and is connected with a beefy clevis-type pin (about 1/2" diameter, I reckon).

Actual hydraulic steering failures would probably be slower to develop (unless a hose or connector fails catastrophically and all the fluid leaks out). Otherwise, slow leaks would make system feel spongy and unresponsive for a while before it gives up completely.
After reading the original post again, I saw that he wasn't talking about a hose connection or a hydraulic fitting at all.

I think you response is right on. If you know what failed it should be pretty easy to correct the problem.
I think that there are times where the numbers on something might work on paper but not so well in the real world. If something fails, beef it up.
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The hydraulic system itself is fine. The ram still moves linearly when the wheel is turned. The break occured at the fitting between the hydraulic ram and the tiller arm. The problem is why?

My rudder post is angled slightly aft (off vertical) as it runs from the cockpit through the engine compartment through the hull. The tiller arm attached to the rudder post therefore swings in a semi circle (as is normal), but at a slightly elevated angle to a horizontal plane due to the tilt of the rudder post. On the end of the tiller arm is a ball, like that on a trailer hitch. The hydraulic ram has a threaded end that received the swivel fitting that attaches to the ball on the tiller arm. This allowed the linear motion of the hydraulic ram to actuate the tiller arm. The ram cylinder itself is mounted on a dual axis fitting so it can move up and down and left to right as it actuates the tiller arm to match the swing of the tiller arm along its angled arc.

The swivel fitting is still attached to the ball on the tiller arm, so the failure occured at the threaded connection to the hydraulic ram. The problem is why? If I just need to "beef" up the swivel fitting, the question will be, by how much and how do I know when enough is enough without waiting for it to break again to find out if it was enough? Any thoughts?
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Quote:
Originally Posted by LittleWingCA View Post
If I just need to "beef" up the swivel fitting, the question will be, by how much and how do I know when enough is enough without waiting for it to break again to find out if it was enough? Any thoughts?
Beef it up just about half again as much as you think you need to and keep the emergency tiller handy.

Seriously, how can anyone speculate without at least seeing what you are talking about.
Post some pictures and we would have an easier time of it.

But bottom line, wouldn't the guy who designed and built this system be in the best position to troubleshoot the problem and correct it?
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Knothead:

I will get some pictures so you can see what I am referring to.

I have already called the guy who designed the system to have him come and check it out, but since it has already failed after roughly one year, there is some doubt about whether he knows enough to fix it properly this time. Hence why I am posting this issue to see if others have had similiar experiences and to see what they did to resolve it. Maybe I will get lucky and find another Maritime Engineer on the forum who might have some suggestions. Let me see if I can post some photos.
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Old 08-13-2008
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I bet your system is Vetus

FWIW (and I am certainly not a naval architect of any kind, just an owner of 36 year old hydraulic steering system), even modern Vetus rams (though smaller than their old versions) are still pretty big. The smallest one (5 cubic inches I think) would have a metal arm (or whatever you call it) almost 1/2" thick. If the fitting bolted on its end broke - there must be some serious problem there.

It sounds like your installation had more freedom than mine in terms of movement. I.e. you have additional movement freedom on the ball that presumably allows the ram to be even less aligned with the tiller arm. On my boat this is a connection that only moves horizontally (i.e. around) - and my rudder post is angled inward quite a bit, so much of the alignment is handled by ram base being angled, and then by ram moving. So, on the face of it, there should be even less stress in your design.

That said, one thing I would suspect is ball connector quality. I think that ball and socket connectors can seize if not lubricated or mated properly. If that happens, then of course force on the connection to the socket would be significant.

With all that, I would be very interested to see pictures of your system and what is broken.

Quote:
Originally Posted by LittleWingCA View Post
The hydraulic system itself is fine. The ram still moves linearly when the wheel is turned. The break occured at the fitting between the hydraulic ram and the tiller arm. The problem is why?

My rudder post is angled slightly aft (off vertical) as it runs from the cockpit through the engine compartment through the hull. The tiller arm attached to the rudder post therefore swings in a semi circle (as is normal), but at a slightly elevated angle to a horizontal plane due to the tilt of the rudder post. On the end of the tiller arm is a ball, like that on a trailer hitch. The hydraulic ram has a threaded end that received the swivel fitting that attaches to the ball on the tiller arm. This allowed the linear motion of the hydraulic ram to actuate the tiller arm. The ram cylinder itself is mounted on a dual axis fitting so it can move up and down and left to right as it actuates the tiller arm to match the swing of the tiller arm along its angled arc.

The swivel fitting is still attached to the ball on the tiller arm, so the failure occured at the threaded connection to the hydraulic ram. The problem is why? If I just need to "beef" up the swivel fitting, the question will be, by how much and how do I know when enough is enough without waiting for it to break again to find out if it was enough? Any thoughts?
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In every hydraulic steering set up I have seen the end of the cylinder is a clevis (fork) that goes over the steering arm with a bolt or pin through it. The other end is usually solidly mounted with another clevis that allows for vertical movement. If the ball joint you mention is what I envision I would change to a much more substantail connection to the arm.

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Brak:

I pulled the invoice for the job now that I am home. The hydraulic pump is a Kobelt 7003 series driving a Marol MSC-28 series linear cylinder with a 82 SER - FEM JIC Swivel attached to the end of the ram.

Jrd22:

The swivel was done because my tiller arm already had the ball fitting on it from my old rack and cable system. The failure is at the ram and swivel connection. The swivel is still attached to the tiller arm, so it looks like the threaded interface between the swivel and ram is what failed. I will have to check and see if the swivel still freely moves on the ball. We have been sailing every weekend for the last 6 weeks, with no trouble until now.

It looks like the swivel is the weak link in the system. The only problem I see with not using a swivel is the non horizontal angle of the tiller arm. A Clevis / Fork might only work if the plain of the tiller arm and hydraulic ram are the same. My setup has the ram capable of 2 axis' of freedom to account for the angled travel of the tiller arm.
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Last edited by LittleWingCA; 08-13-2008 at 01:46 AM.
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