Rudder Cheekplates Replacement

[bob knowles]

Has anyone a source for the aluminum rudder cheekplates? Any ideas as to how to eliminate the corrosion at the steel to aluminum interfaces?

[rogerssp]

I purchased new cheekplates from S2 last summer after breaking a gudgeon and finding severe corrosion. The repair and S2 contact was posted on the old bulletin board if you can find where they hid it. The replacement will corrode in salt water. Plan B is to replace with stainless, avoiding dissimilar metals.

Spencer Roger
Avatar #288

[tburke]

I contacted S2 this fall about replacement cheekplates and the said they no longer provide them. They suggested that I take the old cheekplate to a metal shop and have a replacement made there. Sounds like this is the only alternative. Does anyone have a better idea?

Terry Burke
Vento #499

[bobknowles]

I tried making a set in stainless but the weight was over three times that of aluminum. I had a local machine shop make aluminum copies from the old corroded set. It cost a little over $300 including a black anodized finish. I then reassembled the system using insulating materials between all the stainless harware and the plates (no easy task).

[Dale Eager]

I only have a problem around the pivot bolt hole, but not where the gudgeons mount. The holes are elongated and also corroded to about the diameter of the SS washers. I plan to see if the holes can be repaired (welded and re-drilled?) rather than replace the plates. Anyone know if this is technically and financially feasable?

[Jeff Bonvallet]

The holes on my cheek plates were elongated also. I drilled them out and inserted a brass bushing I purchased at the hardware store for about $2. They last for a couple of years and then I just buy new ones.

I also usually need to repair the pivot hole through the rudder each year, I just fill it with epoxy and redrill it.

Jeff

[Tom Elsen]

Jeff and all, here is a permanent $5 fix for the blade pivot problem.

The piece you need to reinforce the rudder head is a 3/8" x 4" brass pipe nipple. Your pivot bolt (the 'axle') will fit through it perfectly. They're available at most well stocked hardware stores. Cut the threads off of each end (Only the threads, no more). It will be exactly the right length, the width of the rudder head.

Mark the exact center points of your rudder pivots. Mark them on each side of your rudder head. If need be, drill out the rudder pivot hole in the rudder's head to a diameter slightly larger than that of the pipe nipple. Take care to make certain that both sides of the drilled out hole remain centered.

With some duct tape create a cone on one end of the pipe nipple taking care not to expand the outside diameter of the pipe too much.

Mix some semi -soft epoxy. The 3M waterproof product works well. Stiffer ones like Epoxy Stick don't, nor do the thinner 'pump and mix' products.

Coat the inside of the drilled out hole well with the epoxy and leave a bit extra on one side. Push the pipe through that side (It will carry some of the extra epoxy with it as it goes through.) Center both ends.

All of the excess can be removed with a sander.

That's it. You shouldn't ever have a wiggle again...at least not due to the pivot.

[Brian Mellon]

Tom

got all that but the part about the duct tape what was that purpose?

Also as I questioned before is there suppose to be nylon bushings between the rudder head and the casing? I believe someone mentioned he uses CD discs?

Brian

[Tom Elsen]

Hi Brian
The duct tape will keep the epoxy out of the pipe nipple when you push it through the pivot hole. The cone shape helps force the epoxy to the side, rather than just bull-dozing it all out the other side of the pivot hole.
I don't use bushings of any sort, though I can imagine that a Yanni CD would be perfect for this purpose.

[DaveR]

can anyone tell me the makeup of the inside of the rudder at the pivot hole ? my rudder was refinished and I think they made the head to wide - side to side, not front to back - seems like the resulting pressure between the cheekplates ( w/no delrin bushings ) and possibly expansion and contraction of the plates and rudder in hot and cold, caused the top, front of the rudder to crack ( similar to gelcoat spidering but a little more severe). there's some spidering around the pivot hole and when I drilled through (about 3/4 " away from the hole) out came wood ( balsa?) on the bit. I was going to inject some epoxy around the hole to seal it. my rudder is rigged with the brass bushing like T Elson describes. seems like the pivot hole itself is some sort of wood plug with a hole drilled in it, then the foam is poured around it.

[Billy 2-Shoes]

The other day I was having problems (see Tom Elsen's 1/2004 post) centering the rudder bolt hole after dealing with the elongation of the bolt hole by overdrilling the hole, filling it and redrilling. The elegant solution came to me while stuck in the dentist's chair and it works great! I still use round plastic shims at the rudder bolt pivot point...when removed they leave a round worn area on the rudder. Begin by drilling an oversize hole for a rudder bolt (with bearing or shim if desired), cut new round shims and drill them for the rudder bolt, spray 3M adhesive on one side of each shim and temporarily glue one back on. The worn circles make it simple to center the shim perfectly. Wax your bolt really well (I use Johnson's paste wax) and push through the shim and oversized bolt hole. Tape around the bolt head really well to keep it secure....then flip your board over. Now mix a brew of goo......epoxy or fiberglass with filler....and fill the hole. The bolt will stick out past the rudder so just slip the other shim over the bolt, get it centered accurately and press the shim to the rudder. After the glass or epoxy goes off remove the shims and bolt and sand any leaked epoxy flush. This works perfectly and I would guess that it would work just as well for those people using cd's as shims.

[Bob Pr.]

Any ideas as to how to eliminate the corrosion at the steel to aluminum interfaces?

I'm from the S2 6.7, 6.9 & 22 Class Association < http://www.sail-s2.org >. Your magnificent S2 7.9 and our boats share a number of design and construction features because the manufacturing design (as distinct from the Naval Architect's plans) were done primarily by the same person.

For that reason, our rudder heads and kick-up rudder blades are exactly similar in materials and operation to yours, differing primarily in size.

In the 7 years we've been a somewhat organized group, I'm aware of about 5-7 of our boats which have had rudder failures due to failures of the ss bolts attaching the pintles to aluminum cheeks or the similar bolts which attach the gudgeons to the transom.

Through a very fortunate happenstance, I got in contact Dr. Marvin Hack, a metallurgical scientist who is in Grumman's marine division, and he gave us a consult. All that was posted on our BB and I wish I could refer you to those posts. Unfortunately, when our BB was transferred from one company to another, about 6 months out of 7 years of posts were lost. Dr. Hack's posts were in that 6 months.

I would be extremely surprised if your rudder systems have not had similar failures as ours have had because the materials are the same.

As best I recall from Dr. Hack's explanation (which was far more elegant as well as surely more accurate) the contact between the aluminum (Al) and the stainless steel (ss) creates galvanic corrosion due to the induction of currents because of the dissimiliarity of metals in the "table of nobility." The farther apart the metals are in the table, the greater the galvanic effect. And ss and aluminum are fairly far apart.

These currents will be conducted throughout any metals in contact with each other so the bolts attaching gudgeons to the transom can be affected as can those attaching the pintles to the Al cheekplates.

The galvanic corrosion (I hope I'm remembering this right) produces a distentegration/sacrifice of the aluminum (white powder) and the effect of this generation of white powder is frequently to increase the "sealing off" of portions of the ss bolt from oxygen -- it becomes oxygen starved. Whenever ss is starved of oxygen, crevice corrosion occurs which turns the ss into something increasingly resembling crumbly Swiss cheese but without the flavor. When it's become sufficiently "holy", failure occurs.

Dr. Hack said the effects are somewhat capricious and he knows of no way of predicting why, say, one gudgeon bolt, fairly far removed from the aluminum, might fail before a pintle bolt in contact with the Al would, or why one pintle bolt and not another would fail. (The ss bolts holding the Al cheeks together are also subject to this but they're far less critical than those attaching pintles and gudgeons.)

Boats that sail in saltwater probably will be at greatly increased risk for these failures (BUT we've had some occur on freshwater lakes).

Dr. Hack recommended either of two solutions:

#1- replace critical bolts of ss with some made of titanium. Since exposure to oxygen is not as critical for titanium, there will be much less crevice corrosion.

(I've looked for sources of titanium bolts of the size needed but haven't found any.)

#2 - examine and/or replace critical ss bolts every 3-4 years, more often the more saltwater contact there is.

Any errors in the above are due to my CRS memory functions and not to Dr. Hack's very generous explanations.

[Bob Pr.]

It's Harvey (not Marvin) Hack, and he's with Northrop-Grumman not Grumman.

Here are two of his relevant articles:

http://members.shaw.ca/diesel-duck/libr ... rosion.htm

http://www.diveweb.com/maritech/features/uw-su99.01.htm

[Jim]

Ambivalence, #8, has been in salt water for two months now, laying in the Salt River Marina, St. Croix, USVI. I've been unpleasantly suprised by the amount of corrosion I'm finding, including the rudder cheek plates. I'm reassembling them now with a thin insulator between the aluminium and SS; also adding small sacrificial zincs to the pintles.

Has anyone else tried this approach? I'll post my experience.

Jim Kloss
s/v Ambivalence
S2 7.9 #8

[Barry]

What is the correct aluminum alloy for the rudder cheek plates? 6061?
What is the correct alloy for the chainplates?
I can't seem to find this information anywhere.

Barry E
Aeolus #11