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Old 03-24-2016, 02:38 PM   #1
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Very loud rattling noise in lazarette

While letting my cousin drive the '78 Mainship 34 at 2200 RPMs (10knots) I opened the lazarette and discovered a horrifically loud rattling of the steering piston. When I firmly grab the piston the noise stops.

Any ideas what's causing this, and how to fix? It's a major contributor to the overall noise and it can be heard in the cabin.

I am planning on fairing the keel at some point, so hopefully that will remove some of the turbulence. Could a bent propeller blade cause this?

Thanks,
Robert
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Old 03-24-2016, 02:48 PM   #2
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Cavitation running past the rudder(s) would be a possibility. Did you check where the rudder bolt(s) come through the hull to make sure everything is tight?
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Old 03-24-2016, 02:57 PM   #3
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Everything feels tight, although it could just be corroded tight. I dove under and inspected everything a few months ago when I first discovered this and everything looked normal, very little play in the rudder. Is there a specification for how much lateral movement there should be at the bottom of the rudder? My guess is I have less than a quarter inch measured underwater at the bottom, pushing and pulling from side to side.

Thanks,
RR
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Old 03-24-2016, 02:58 PM   #4
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Tighten the stuffing box a bit...even if it isn't leaking. The rudder movement is slow so friction isn't an issue for heat.

See if that helps...also tighten any screws, bolts that may hold un upper bearing before the ram or at the other end of the ram.

You could also have something on the leading edge of the rudder...have you blasted it in reverse yet?

You would notice your shaft vibrating pretty good if it were the prop.
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Old 03-24-2016, 02:59 PM   #5
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Clearly there is play in something if grabbing the cylinder stops the noise. It should be simple enough to move it around at the dock to discover what's loose. Probably a loose bolt or worn bushing, got any photos?
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Old 03-24-2016, 03:07 PM   #6
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I opened the lazarette and discovered a horrifically loud rattling of the steering piston. When I firmly grab the piston the noise stops.
-----------------------------------------------------------------------------------------------

I assume you grabbed the cylinder, not the piston??

Maybe the cylinder is loose in its mounting. Both ends of the cylinder will be mounted so the cylinder can swing in an arc to move the rudder arm.
If those mountings have worn and have excess play then maybe the cylinder is rattling.

The rod end clevis that attaches the cylinder rod to the rudder arm can wear the hole in both the arm and the clevis although usually the clevis is softer so wears first. Replace the clevis. or rebush it.

The opposite cylinder end may be mounted differently. Some are mounted on a simple pivot built into the cylinder end or they may have a more centre mounted pivot. Regardless these can also wear.

These pivots , both, should be greased periodically. A heavy oil would be suitable also but need to be done more frequently.

But at this point you may need to do some repair if the looseness is excessive.

It is also possible for a machine shop to rebush the pivots but look at the cost one way or the other before deciding.

The next question would be if the boat vibrates excessively from poor engine mounts, prop damage, or a shaft [and mounting] problem.

Deal with the cylinder first but consider whether the vibration is excessive.
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Old 03-24-2016, 04:35 PM   #7
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I was holding the cylinder. There is a normal vibration in the hull from the engine. The cylinder has a nylon ball joint where it mounts to the hull. Unfortunately it's an outdated teleflex sytten version with no available parts.

There is a slightly excessive drip from the packing that I've been meaning to address, but I had no idea that could be related. I'm planning on diving under tomorrow to inspect and measure for a fairing block for the aft edge of the keel. I'll try to get some sort of play measurement on the rudder while I'm down there.

Thanks,
RR
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Old 03-24-2016, 08:26 PM   #8
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The cylinder is quite likely the telegraph.
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Old 03-24-2016, 10:38 PM   #9
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I wouldn't think you would need to dive to find the loose point in the system (unless it is at the bottom of the rudder). It is the cylinder or the piston end, the tiller arm, or the fit of the rudder shaft.
Your rudder is going to vibrate to some degree no matter what you do. But with 1/4" play (that you mention) to hammer away at your noise is only going to get worse.
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Old 03-24-2016, 10:56 PM   #10
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Prop noise. Normal on a full keel boat at 10kts. That's not a good speed for that hull for a couple of reasons, slow her down and she will quiet right down. Turbulent water going into prop will raise all sorts of hell in the lazarette.
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Old 03-25-2016, 02:02 AM   #11
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Rudder stock needs more packing.
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Old 03-25-2016, 05:53 AM   #12
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A recently discovered scourge on TF - under loading per chance?
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