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Atlantic Salt · 13-06-2016, 13:47

I was ready to go in the water a week ago. Last thing was to put steering wheel on my C&C Frigate 36. Did that but wouldn't turn! turns out the bronze stuffing box (Edson) and the aluminum rudder post corroded together. Tried variety of sprays and penetrating oils, heat, cold and brut force with drift and hammer and 3' wrench. The thing won't budge. The thing is it was newly installed last year and I sailed the boat for about 3 months before pulling out for the winter.

I was surprised to find many if not most rudder posts are aluminum.

Has anyone had a similar experience or suggestions. I'm at the point to cut the shaft and have new rudder built (machine shop said "old" aluminum likely won't take a good weld if I try to put on a new start only).

Frantic!!

Schrewsburyduo · 13-06-2016, 13:56

rudder post should be SS. ask for a refund...

barnakiel · 13-06-2016, 14:04

Not all stocks are alloy. I have seen bronze, SS, alloy and carbon shafts, both solid and thick wall tubes.

Alloy close to bronze in saltwater may trigger trouble. Maybe you can benefit from a fenolic cutlass / bearing in place of the bronze one?

Truly frustrating. I hope you will find a possibly non destructive solution.

b.

RaymondR · 13-06-2016, 14:18

Alloy is a very poor material from which to manufacture a rudder stock, particularly if you put it through a bronze bushing underwater, it will act as an anode to pretty well any other metal it is submerged with. If you can get the rudder and bushes out replace the bronze bushings with polymer ones and in the longer term plan on replacing the alloy rudder stock with stainless tube.

Cheechako · 13-06-2016, 14:32

I've never seen a aluminum rudder post on a fiberglass sailboat. Not fond of that. Aluminum is < 40% the resistance to bending than SS. (ie: deflects under the same force far more) In theory the rudder shaft shouldnt even be touching the bronze packing gland, but then there's reality I guess. :>)

barnakiel · 13-06-2016, 16:50

Aluminum is quite common a material here.

E.g. rudder posts in newer Najads, WindPilot windvanes, Etc.

I think it is all about the wall thickness or rod thickness and then about the materials that surround it - bearings, etc.

b.

**tkeithlu** · 13-06-2016, 17:32

RaymondR speaks with wisdom. This is one damned serious mess. The rudder shaft should be stainless steel, not aluminum, not just for strength but for corrosion and elasticity - steel springs back when aluminum stays bent, the shaft should not have had the opportunity to actually touch the bronze, but be separated by the stuffing and a non-corrosive bearing, and that rapid corrosion suggests a bad anode problem. Is the prop and its shaft OK? What do the anodes look like?

Atlantic Salt · 13-06-2016, 18:55

Want to point out the original aluminum/bronze combo lasted over 40 years. Then replaced fitting and corrodes in 1 year. Hard to figure. I'm leaning toward replacing rudder with s.s. Shaft and fg.

Sent from my iPad using Cruisers Sailing Forum

RaymondR · 13-06-2016, 23:36

Here's an off the wall theory.

For galvanic corrosion to occur you have to have an electrical circuit in which the current can flow.

I believe the theory is that the dissimilar metals in the presence of an electrolyte (water) set up a potential difference but if there is no return current path the potential cannot drive any electrical current flow.

Normally the packing in the gland would hold the two dissimilar metals (alloy and brass) apart and consequently they would be insulated from each other ie no return current path.

However, if the gland was packed with a packing which contained graphite grease and was conductive an electric circuit might be established. graphite = carbon = electrical conductor.

My rudder stock jammed in the tube because of internal corrosion in the carbon steel tube. I got it free by making a clean out tool from a piece of steel pipe which I split long ways and removed a section of the circumference of the tube and formed teeth on one end with a grinder. I then forced the toothed end down into the annulus between stock and tube and turned it with a pipe wrench. Between turning and banging it in with a hammer I ground out all the rust in a couple of hours and freed up the rudder.

Good luck on your repairs.

F10 · 14-06-2016, 12:37

If you have not already, try the penetrating oil PB Blaster-
Products | The B'laster Corporation
http://blastercorp.com/PB-Blaster-Pe...ck-parts-spray
let is soak for three days while you keep it wet with the PB Blaster. The use some force on it to try to break free. Using heat to try to expand the outer sleeve of the two parts may also help- but don't set the oil and you boat on fire.

barnakiel · 14-06-2016, 15:03

I suggest our poster who mistrusts alloy as a rudder stock material looks into this:

Jefa Rudder bearings

Jeffa is a top shelf company making new rudders. I am 100% certain they are pro people and would not suggest aluminum if it were not a reliable material.

Cheers,
b.

F10 · 14-06-2016, 15:13

Quote:

Originally Posted by barnakiel

I suggest our poster who mistrusts alloy as a rudder stock material looks into this:

Jefa Rudder bearings

Jeffa is a top shelf company making new rudders. I am 100% certain they are pro people and would not suggest aluminum if it were not a reliable material.

Cheers,
b.

More info from their site:
Jefa Rudder bearings

Characteristics of aluminium:
The mechanical and anti-corrosion characteristics of aluminium depend on the alloy elements. Pure aluminium is not usable for a high strength purpose like a rudder shaft. The most popular aluminium alloy for rudder shafts is AlMgSi1 (EN 6082). The addition of the alloy element manganese extremely increases the mechanical properties proof stress and tensile strength. The addition of the alloy element silicon extremely increases the corrosion resistance of the aluminium. A hard and strong layer of silicon oxide SiO2 protects the aluminium even against the most hostile seawater. We use the following types of aluminium:

Aluminium AlMgSi1 (EN 6082)
The tensile strength is 340 N/mm2 , the 0.2 % proof stress is 280 N/mm2, the specific weight is 2.700 Kg/m³.
Aluminium AlZnMgCu1,5 (EN 7075)
The tensile strength is 520 N/mm2 , the 0.2 % proof stress is 460 N/mm2, the specific weight is 2.700 Kg/m³.

Atlantic Salt · 20-06-2016, 08:27

Thanks to everyone for taking the time to reply. I thought I would update you all on what I am doing about the rudder.

I also note that the term "alloy" was used by several posters and this confused me as most of the metals we use are alloys. Steel is an alloy of iron and carbon. Stainless, and there are several types is also an alloy containing chromium (I think). similarly, there are several alloys that use aluminum as the base - some will work on a boat and some won't. My boat was built in 1970 so at that time perhaps the aluminum alloy that was used was not as advanced as the ones they use today.

Anyway, I sawed the rudder post to get the rudder off. I was also advised by a welding shop that old aluminum sometimes does not take a weld very good. Also I would still be left with almost the same situation as I encountered this year. SOOOO, I am in the process of having a new 11/4" 316 s.s. post with 1/8" vanes made up to which I will epoxy layers of 3/8" divinycel with 6 oz cloth between. Then I will shape as I wish and encase the whole thing with 18 oz woven cloth with a matting sewn to it. The matting goes on the outside and becomes sacrificial when sanding. Barrier coats and then antifouling. Fairing with low density filler before the barrier coats.
I'm part way through the process now. If interested I will post the final results when finished.

Again, thanks to all.

phil