Rudder "Flutter"

[Cpy23ecl]

Just curious if others experience what I'm encountering.  Once boat speed gets to 4kts and above my tiller starts fluttering back and forth a tiny bit as if there's some sort of turbulence on the rudder.  It's not severe and not a big deal but I can't say I've ever had this on any of my other boats.

Fred

[brackish]

I've had that happen on my 23IV on occasion.  It has a factory foiled rudder.  I can't tell you what conditions cause it, have never figured it out.  When it happened, I bought the pin hardware to rebuild the pintles and gudgeon joint thinking there was some slop in there.  When I hauled out, I found the joints to be tight, no play, so that wasn't it.  At least I have the hardware if I ever wear them out.

As you said, minor thing, only occasionally, so I just ignore it.

[slode]

What frequency is the "flutter"  I've never experienced anything with high frequency, but the rudder will "flop" back and forth a bit when sailing in choppy waters.  As the boat rolls slightly the force on the rudder with switch from side to side.  New gudgeon bushings will help, but there is always just a bit of slop in the assembly. 

I have felt the centerboard vibrate at higher speeds on anything downwind of a beam reach.  That is higher frequency and can be felt through the tiller.  It's just the nature of a pivoting centerboard setup.  If you really get her moving downwind you can experience some vibration in the standing rigging too.

[Cpy23ecl]

I would estimate the flutter occurs at a frequency of approx 4 to 6 times per second and only when boat speed approaches and exceeds 4 kts.  Its definitely a vibration as opposed to a flop.  If I let go of the tiller the forward end of the tiller moves side to side maybe a 1/8 to 1/4 inch or so.  We were sailing in water that was essentially flat, 6 inch or less waves.  Rudder bushings are tight as the boat was purchased new and has only been sailed 6 or 7 times to date.  My feeling is that its turbulence induced by the the foil shape.

I have felt some "thunking" in the tiller when sailing in 3 to 4 footers last year.  My guess is that I didn't have the rudder blade hinge bolt quite tight enough.  I haven't felt it this year but haven't been out in conditions like that this year.

I've also noticed a bit of vibration from the centerboard pendant at higher hull speeds which is to be expected.  My first sailboat had a cast iron swing keel with a cable pendant that vibrated such that the sound it made reminded me of humpback whale songs.

Fred

[Andre]

Fred,

Is there any possibility that the rudder blade assembly (the lower part that pivots up) is a bit loose in the in the upper part (bracket?) and so it wiggles a bit?  I shimmed mine on my HC (it looks like the Eclipse uses similar parts) with a "washer/spacer" cut from a polyethylene windshield fluid bottle. I made mine oversize rectangular so I could move it around until the holes and pinch bolt lined up and then trimmed it up once it was in place.

I did this NOT because of a vibration issue but because of a failure in the cast(?) rudder bracket that I saw on YouTube that seemed to originate right around the pinch bolt. I suspect that it was due to over tightening of the pinch bolt and thought that this might help to prevent this.

Andre

[Andre]

Here's the video.
https://youtu.be/RtJYHKymzlA

The failure occurs at about 1:30, the rudder can be seen floating away (it floats!) at around 2:00, and the broken bracket shortly thereafter.

Correction - Looking at it again it looks like it failed above and not at the pinch bolt.

Andre

[Cpy23ecl]

Wow.  That would ruin your day quickly.  My initial reaction is I don't think the blade is loose in the casting as I it feels like the rudder blade, casting, and tiller are all moving together.  I have the blade pivot bolt tight enough that the blade stays up without using the rod that keeps the blade up or down.

That said next time I go to the boat (its 400 miles away from my house) I'll check that carefully.

[bruce]

Thanks, Andre.

Many Com-Pac, and other boats, share that design. It does look like metal fatigue, but, fortunately, we haven't heard of that many failures. Good to check out, as best we can.

[Andre]

Hi Bruce

I agree with your fatigue failure statement. I suspect that the normal flexing due to the rudder forces superimposed on the clamping bending led to the casting failure. My thinking in putting in the thin spacer was that it would reduce the bending in the bracket required to securely clamp the rudder in place. Less bending results in less stress on the piece.

Andre

[bruce]

I agree with your shim idea, that would reduce the metal fatigue.

I'm less apt to suggest shims made up of random plastic bits. Great if they work, but plastics are engineered as well as other materials. Choose sheet stock designed for the task. Some designed UV and marine tolerance in this case. If supplies are limited, Mcgyver away!