Rudder shudder

[ChasRN]

I got out on Weds for the first time with my new-to-me boat, Cat-22. Since she's been renamed (yes, I did the formal ceremony), I guess this outing qualifies as a combination maiden voyage and shakedown cruise. With my only other sailing experience on J-27's, I'm impressed by how easy Sun Cat's are both to rig and sail.

That said, I'm curious about one aspect of her sail performance, a vibration felt at the tiller. Describing it as "rudder shudder" may be a bit hyperbolic, but the vibration is clearly noticeable even if not really alarming. It's greatest when the rudder is centered and ebbs/disappears when the tiller is put over. In terms of positioning, the rudder was in the full down position with the tension handle tightened up, but I did not have the lockdown pin inserted.

Is this a case of "they all do that" or is there something out of adjustment? She's on a dry slip at present, so access for maintenance/adjustment is not a problem.

[mikehennessy]

I have the same thing and it appears when at a certain speed.  If going slower or faster - no.

Was told grinding off part of the edge of the rudder would help but I have not tried.  Suspect it is caused by turbulent flow over the rudder.

Anybody had a cure without spending a bunch of $ on a new one?

[bruce]

Mike,

Did you ever try shimming the rudder blade in the rudder head as Roland suggested? Any old plastic sheet should hold up well enough to test the concept.
https://cpyoa.com/forum/index.php?topic=11471.0

[mikehennessy]

Good memory Bruce!

I'll try it my next time out and report back.

Made it out 6 times so far this spring.  Added a downhaul and it works well.

-Mike

[ChasRN]

I have the same thing and it appears when at a certain speed.  If going slower or faster - no.

Was told grinding off part of the edge of the rudder would help but I have not tried.  Suspect it is caused by turbulent flow over the rudder.

Anybody had a cure without spending a bunch of $ on a new one?

Does "grinding off the edge" mean feathering the trailing edge?

[mikehennessy]

The trailing edge was my understanding but I did not try.

Bruce had added a previous note about possible shimming the rudder.  This year the rudder shudder had been much less than last year.  When I went out yesterday I made sure I tightened the nut very snugly and didn't experience any shudder.  One data point does not make a line so I'll continue the study.

[bruce]

My guess is that shaping the 3/8" aluminum plate rudder on the leading and/or trailing edge won't make much of a difference. Before I started grinding away I'd try adding some pre-shaped material on the edges to test the concept. Doesn't have to last long, just hold up for a few sails.

For example, this half-round plastic molding in 10 mm would work on the leading edge. Cut to length, tack it to the edge with hot melt, and run packing tape along the molding, sealing it to both faces of the rudder. The tape wouldn't be thick enough to cause significant turbulence. The aft profile should be more of a tapered wedge. Wood would be OK for the short term, seal it if you want. Both profiles would be easy to make on a table saw and router. Doesn't have to be fancy. A round dowel might work on the leading edge, the tape fairing the transition to the plate on the sides.

https://embellishfx.com/lumins-workshop-half-round-eva-foam-dowels/?dfw_tracker=61967-3055-0000&utm_source=google&utm_medium=cpc&adpos=&scid=scplp3055-0000&sc_intid=3055-0000&gclid=Cj0KCQjw3Nv3BRC8ARIsAPh8hgI4pwyqGVsC_0PjclzKFbjhgvba6G0B40wdP9gJlMyCdRTOEih1kzYaApfOEALw_wcB

[ChasRN]

I have another rudder issue as well.

Movement seemed to bind just a bit when the tiller was pulled over, so I decided to try to clean and lubricate the bracket. I was able to get the upper bolt out easily enough but the lower seems firmly attached to the bracket. The upper bolt has a smooth upper and is threaded only at its lower end and is secured to bracket only by the attaching nylock nut.

I assumed that the lower bolt is the same but even after using a liberal amount of penetrating oil, it stayed frozen. It was impervious to a few moderate blows via the rubber hammer hammer I had with me (the boat is in a dry slip some distance away), and I was not even successful in turning he bolt via a socket wrench at the head. The bolt seems pretty frozen to the bracket, though it does turn when the rudder is moved.

Before I try a higher level of persuasion  - a small sledgehammer via a steel drift inserted through the upper bolt hole to the threaded end of the bolt - I thought I'd check to make sure that my assumption above is correct. So is the lower bolt is identical to the lower i. e., not threaded in the bracket?

[bruce]

Bubs thread on weather helm has a couple of posts with photos that should help, Tom's on p.4 and Roland's on p.3. They both show a through bolt, and report a bronze bushing in the gudgeon, likely the pintel side as well. Tom had problems getting his lower bolt out, closer to the water.
https://cpyoa.com/forum/index.php?topic=11263.msg85821#msg85821

If the bolt is trashed in the process, it will be easy to source. Heat could help, a soldering iron will put the heat were it is needed, control being important! Giving the penetrating oil more time can make the difference as well.

[ChasRN]

Thanks Bruce.

I will bring my propane torch with me when I go to tackle this again. She's on the trailer in a dry slip, so relatively easy to do the repair. I'm hoping that a few taps with a sledge will be enough to get things started - once the head of the bolt is clear of the bracket, things should go easier.

I have more work (sigh). When I was out with my son yesterday a sudden wind shift resulted in the boom coming quickly around. Not quite an accidental gybe but enough strain to cause a sail slide to break off. Before I could drop the sail, the increased strain caused several more to break. It did not seem like a lot of force, and all the slides broke off, leaving their bases in the sail slot, so maybe it was just their time. But poor seamanship certainly played a role.

I'm learning a lot about sailing and even more about boat repair . . .

[bruce]

Careful with the torch, the gelcoat and resin would be easily damaged. I'd try heating a piece of metal and holding that against the suspect areas, if necessary. Hopefully the penetrating oil will have done it's job by then.

Never heard of all the slugs failing, they may have been deteriorated. Not sure what slugs you've got, on the PC we have Bainbridge A017 NYL INT Slug Slide 3/8". They are marked Bainbridge and A017 on the cylinder.

Looking at the SC parts list, they seem to be 7/16", part #MRJSS0146. I'd guess they're Bainbridge A018, hopefully they're marked, or you can get them from Com-Pac. Cheap enough from anyone.
https://www.dropbox.com/sh/xtfxq40jvl9esw9/AADHttjwMACdw5Voo2NYBoLVa?oref=e&preview=SUN+CAT+2018.pdf

Bainbridge does make 11mm slides with SS loops, A018S, if you want to make your sail the weak link
http://www.bainbridgeint.com/Variants.aspx?Item=PRD-900102

[ChasRN]

Thanks again Bruce.

I saw that the ComPac lists them as 7/16" and that they are among the most inexpensive items in the catalog. Just as well since I think it's probably prudent to go ahead and replace them all. I guess I should also order some whipping twine though the webbing at least looks like it's in reasonable shape. I hope my sewing skills are up to the task.

It also looks like the only way to get the slides off is to take the upper sleeve of the MasTender off.  Like I said, I'm learning a lot about maintenance and repair of the Sun Cat . . .

[bruce]

No need to take the Mastender off the mast or stub. With the mast down, just remove the 2 pivot bolts and set the mast aside. You can lift out the gaff gooseneck, to get to the slug fragments. 

The pivot bolts have been known to fall down the mast stub, so I stuff a rag in the stub before I start.

[bruce]

Also, I checked a few photos of Sun Cats, and I see at least some use nylon shackles, with screw closures, to connect to the slugs. Jim in TC's boat has them I think. Sure enough, part #MRJSS0145 on the CP parts list is: Shackle for sail slug, $1.70. Even cheaper than the slugs!

Sewn webbing is nice, but...

[mikehennessy]

Tightening the bolt extra tight to reduce the space between the rudder and rudder sheath did not produce the desired results today.  Still had shudder.

Will try a shim next week.