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Old 07-03-2018, 07:01 PM   #1
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Can my rudder cause vibration?

I was on the yard last August, the yard said the rudders needed to be dropped and machined, there was some slack where the rudder gear hits the (for lack of better words) turning gear. Iíve been trying to figure out a vibration that I experience when pulling boats at about 1300 rpms. The less I pull the less vibration I experience.
I check the alignment one both engine several time so Iím down to the props, which were worked over in August, bent shafts or loose rudders?
What do yíall think?
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Old 07-03-2018, 07:12 PM   #2
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I had a vibration in my rudder, moved the anodes out of the wash and welded an angle on the trailing edge - no vibrations.
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Old 07-03-2018, 07:21 PM   #3
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If youíre not towing something does it vibrate?
Are the rudders and props clean?
When vibration occurring can you isolate by feel to the rudder shaft?
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Old 07-03-2018, 07:33 PM   #4
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yes, loose rudders can vibrate, but usually vary as you change rpm...

also IF you had a badly balanced/damaged prop...they can shake a rudder pretty bad.
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Old 07-03-2018, 07:55 PM   #5
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I only thought about it after my last trip, my buddy was on the back deck and said he felt it vibrate worse when I was turning
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Old 07-03-2018, 08:17 PM   #6
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Can you see the rudder shafts when you are underway? Maybe lay your hand carefully on the rudder shaft and see if you feel any vibes.
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Old 07-04-2018, 01:01 AM   #7
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Ruddershafts typically wear in the bushing, where it passes through the hull.
I have seen rudder shafts that were worn to a visible oval shape where they pass through the bushing, and they do rattle, usually in sync with the propeller blades.
I always install a grease fitting in the bushing and give it ashotof grease regularly.
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Old 07-04-2018, 08:41 AM   #8
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Go in the hole and look at the rudder gear from inside the boat when you have the vibe. If things are too loose you will see it moving around.

If everything is rock solid, vibe is coming from something else.
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Old 07-04-2018, 09:55 AM   #9
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The SS rudder shafts wore at the bottom where the enter the bushing, bronze bushing was ok. That was after 40 years of boat use. You could hear it when the boat would go up and down with the waves, like click clack. Wear was on the trailing back part of the shaft.

The rudders had at least 1 inch of exposed SS shaft. What I did was raise the rudders up so they were fully in the bushing, so they were tight and good and no more noise. I also greased with marine grease bushing and shaft. Rudder shafts are 1.25 inch diameter so even 1/8 inch of wear is not a problem. Other than that shaft wear at the bottom of shaft, the shafts were spotless. I also used GFO packing on the rudders.
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Old 07-04-2018, 10:17 AM   #10
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No doubt they could vibrate even if they were sufficiently snug in their bearings.


The rudders of our Morgan 27 and our LeComte NE 38 would vibrate at speed. The rudder of a Flying Dutchman sailing/racing dinghy positively buzzes at speed.
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Old 07-04-2018, 10:38 AM   #11
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Try the gudgeon pin that connects the steering rod to the ram, old Wagners did not have a grease fitting there, replacement pins do.
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Old 07-04-2018, 12:10 PM   #12
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I made sure my twin rudders had a little toe-in. This tends to load the rudders a bit when underway and reduces chatter in a loose system.
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Old 07-04-2018, 12:49 PM   #13
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Not rocket science if the vibration stops when you turn the rudder system is at fault
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Old 07-05-2018, 07:39 AM   #14
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Quote:
Originally Posted by bayview View Post
Not rocket science if the vibration stops when you turn the rudder system is at fault


Well the vibration gets worse when turning
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Old 07-05-2018, 08:28 AM   #15
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If the prop wash is significant, even in a turn I would think the rudders can flutter from prop pulses....overcoming the loading in a turn.

No wizard here.... sort of sounds like cavitation induced.

Starts at a certain RPM when towing and increases with RPM without significant speed increase.
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Old 07-05-2018, 08:43 AM   #16
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I see that you say pulling boats and more load makes it more apparent. Cavitation is possible as is prop to hull clearance. Has it always done this? Was it better before the props were worked on?
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Old 07-05-2018, 09:46 AM   #17
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Normal for vibes to go up in a turn. The prop noise on my boat goes way up in a turn. I can tell it is in sync with blade passing frequency. Sort of a "hum".

Helpful to know if Swamp's vibe is in sync with shaft rotation (wiggle) or blade passing frequency (hum).
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Old 07-05-2018, 09:46 AM   #18
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I donít know how long itís been doing this, I just last year got her going. The problem was worse before the prop work, the props are old and deteriorating, the prop guy said he did the best he could do but I probably need new props, I was just trying to make it bearable for a season until I get her back on the yard
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Old 07-05-2018, 09:49 AM   #19
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I would say the later Ski, itís more of a harmonic hum, maybe every 3 seconds or so at its worst, only on the port side
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Old 07-09-2018, 01:11 PM   #20
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Originally Posted by swampu View Post
I was on the yard last August, the yard said the rudders needed to be dropped and machined, there was some slack where the rudder gear hits the (for lack of better words) turning gear. Iíve been trying to figure out a vibration that I experience when pulling boats at about 1300 rpms. The less I pull the less vibration I experience.
I check the alignment one both engine several time so Iím down to the props, which were worked over in August, bent shafts or loose rudders?
What do yíall think?
Vibration and noise is cumulative. There are always some larger sources, but attending to them all over time helps. In the case of a rudder or other critical mechanical member, it is important to make sure they are operating within spec. A shudder in a shaft or rudder can affect seals and stress fittings. Best to handle the issue - you'll ride smoother and your boat will be better for it in the long run.
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