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. I’ve 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 I’m down to the props, which were worked over in August, bent shafts or loose rudders?
What do y’all think?

I had a vibration in my rudder, moved the anodes out of the wash and welded an angle on the trailing edge - no vibrations.

Questions
If you’re not towing something does it vibrate?
Are the rudders and props clean?
When vibration occurring can you isolate by feel to the rudder shaft?

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.

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

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.

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.

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.

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.

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.

Try the gudgeon pin that connects the steering rod to the ram, old Wagners did not have a grease fitting there, replacement pins do.

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.

Not rocket science if the vibration stops when you turn the rudder system is at fault

bayview said:

Not rocket science if the vibration stops when you turn the rudder system is at fault

Click to expand...

Well the vibration gets worse when turning

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.

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?

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).

I don’t know how long it’s 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

I would say the later Ski, it’s more of a harmonic hum, maybe every 3 seconds or so at its worst, only on the port side

swampu said:

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. I’ve 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 I’m down to the props, which were worked over in August, bent shafts or loose rudders?
What do y’all think?

Click to expand...

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.

Good ole rudder shudder or rudder flutter. :lol:


Yep. It's a thang. I had it happen to a ski boat with a stright gas inboard. It had two supports, one where the shaft entered the hull and the other at the top of the shaft. The bell crank to turn the rudder was traped between the two supporting bearings. At certain speeds, she'd get rudder flutter and it sounded like the transom was going to blow apart. Watching the upper bearing, it could be seen that the shaft had movement. It couldn't be felt or moved when the boat was on the dry but with the forces from the prop wash and moving through the water, it was more than noticeable.