rudder discussions

[sinbin]

Looks just like mine, but I kept the bolts.

[sinbin]

Bob of A100: Got your msg. Need your e mail address. Thanks, Dennis.

[pbryant]

I just recently had a haulout at Svedsen's and noticed some of the notorious corrosion of the bronze rudder shaft at the water line. It was pink (dezincification?) and appeared a little thin. I had the rudder taken off for a closer inspection. It looked a little worn, and so I decided to have Svedsen's replace it with a 316L stainless shaft.

After they took the rudder off the shaft, it was clear that there was only about a tenth of an inch of uncorroded bronze holding the shaft together at the waterline and at each fastener penetration hole! One hard shove and I would have snapped the shaft. So my purpose for posting this is to caution the reader that if any corrosion is present - it may be a lot worse than it appears. The corrosion easily hides in the areas covered by the rudder and attachment screws.

I'm glad I had it replaced because I had to traverse the Golden Gate Bar in heavy swell to get back to Half Moon Bay, and for the first time I had to navigate over the bar all the way out to the end of the deep water ("main ship") channel to avoid plunging breakers on either side. This was my tenth crossing in and out through the Golden Gate Channel, and the swells from the recent storms made it exciting - I wouldn't ever want more excitement. I'm posting here the course that I took over the bar and the full voyage. I had 10 foot following seas all the way back to Half Moon Bay (surfing at 6 to 8 knots!), where I had to reverse the rudder every 10 seconds to compensate for reversed flow across the rudder caused by oncoming swells. The rudder got quite a workout and the new shaft was essential!

Had I not followed the proper course to avoid the breakers and avoided going through at max ebb tide, I am sure I would not have made it across the bar in those conditions. Previously, I'd always been able to plan my bar crossings in less than 6 foot swells, but this time of year, I could have been trapped in the Bay for some time waiting for those benign conditions to develop. I highly recommend this article to anyone who plans to cross the bar: http://coastsidefishingclub.com/grey...francisco-bar/ -- especially the sections on "Crossing the Bar Tactics" and the mythical "South Channel" (why is that name even on the charts?). It's written for fishermen in motor boats, but the advice is just as valid for us. Capsizing is capsizing.

[Bill]

Replacing with stainless instead of bronze may increase the incidence of corrosion over time. Rudder shoe and other below the waterline fittings are bronze.

It's recommended that you keep a zinc on the shoe. That will protect it and the lower rudder shaft.

To protect the upper rudder shaft, I attach half of a jump cable to the lower portion of the tiller head fitting and drop the other end into the water with a zinc attached. (Remove the cable clamp and attach the zinc to the copper wire.) Of course, if Svedsen's replaced the two shafts with one, the upper cable attachment is not necessary.

[pbryant]

Thanks. I'm floating a large zinc that I sink at the slip. I'm using stainless steel alligator clips connected by stainless steel braided wire I got tired of replacing seawater-dissolved copper - copper turns to green powder practically overnight. The attachment point is the bolt retaining the tiller head.

[ebb]

DO NOT REPLACE YOUR RUDDER SHAFT WITH 316L.

The only material to use is readikly available 655 SILICON BRONZE.

316L is NOT A PERMANENT UNDERWATER METAL.
If you are going to the expense of having a rudder made
use only silicon bronze.


You will be creating a galvanic corrosion situation with the heel fitting
and the gudgeon strap. Zincs won't immunize a galvanic system.
[A338 came to me with a rudder of unknown stainless steel shaft that caused
the heel fitting to get eaten away. There were zincs attached to the heel fitting.]

Bronze used in underwater suituations must have very little or NO ZINC. Use S.B.
which is 98% copper. It is as close to an inert metal you can have in salt.

Silicon will survive the waterline corrosion anamoly in the rudder tube
- 316L will not. Bet on it! This is especially true in a marina situation.

You already may have to have a new heel fitting made.
Look for corrosion there. You do NOT want to seat stainless into a bronze heel fitting.

Have a new one cast of silicon bronze (to match your new S.B. rudder.)
Can be done locally in Richmond.

[pbryant]

There must be an awful lot of stainless propeller shafts with attached bronze propellers in peril of corroding away out there.

[ebb]

Propeller shafts are not made with 316L.
Drive shafts of "Aqualoy & 17-4 Aqumet" are alloys of twice the strength of 300 series s.s.

Also the propeller/shaft system is 'isolated' from other underwater metals like the rudder.
You'd have galvanic problems with any mixed metal combo.

Best drive shaft and propeller would be all bronze.

[pbryant]

https://www.google.com/#q=stainless+...ropeller+shaft

For rudder shafts:

"Historically stainless steel 316 has been the preferred rudder shaft material. This material was chosen as it was non corrosive and relatively strong and widely available."
http://www.jefa.com/products/materials.htm

I work with a bunch of metallurgists. Their consensus was that, although no metal will last forever in seawater, SS 316L with an attached zinc will hold up longer than silicon bronze. I actually doubt the original shaft was silicon bronze. The pink discoloration indicates the presence of zinc.

[ebb]

Your friends are misinformed.

If your friend only knows about stainless,
are you going to ask him about silicon bronze?


I once had a curmudgeonery exchange with Roger Winiarski of Bristol Bronze,
who told me his company supplied the original Ariels and Commanders with the bronze used for the rudder and cast heel fitting.
He said they used manganese bronze - which has zinc in it.*

Now, I know you are impressed with EXPERTS - and so am I -
but Roger had no answer for using M.Bronze for underwater cast bronze. (not sure about the shaft - but it appears Bristol supplied the wrong stuff for your boat which probably lives in a modern HOT marina.)
There is no answer. Bristol sold the wrong material to Pearson (or maybe it was the cost effective compromise to the correct material).....
But good enough to last 40-45 years.

Silicon Bronze is the right stuff.
Manganese Bronze is and was the wrong stuff.
300 series Stainless Steel is and forever will be the wrong stuff.

for your Ariel/Commander rudder.
.................................................. .................................................. .................................................. ..................................................
*Has been a long time since going through Bristol Bronze's catalog.
But I think I recall seeing a heel fitting listed there that specifically said it was silicon bronze.
.................................................. .................................................. .................................................. ..................................................
later edit. All common bronze plain and threaded rod, fasteners (machine cap screw and wood screw, bolts, nuts, washers) are usually silicon bronze. Less and less as years go. But you can still build a bronze armmature rudder with 665 Evadur sheet. welding rod, and common fasteners. It'll just cost you. Blame it on Wall Street. Check out Top Notch Fasteners tnfasteners.com Also OnLineMetals, McMasterrCarr & Duckworks.

[pbryant]

Yeah, I thought there was some zinc in there. Manganese bronze is bronze in name only; because of its zinc content, it resides squarely in the brass family. I agree with you that manganese "bronze" (brass) is the wrong stuff.

And, OK. I guess my friends are wrong. You never can trust those NASA engineers who fabricate stuff for research vessels...

Here's another reference:

"The stainless steels often used for propeller shafts include Types 303, 304, 316, and 630. All stainless steel shafting is strong, especially the 630 type (which is also known as "17-4 PH"). Stainless steel shafting in salt water is more-or-less subject to pitting which leads to crevice corrosion. Types 303 and 304 are probably worse in this respect, with type 316 being less susceptible, and therefore better suited to salt water use. The 630 type is probably neck-and-neck with K-500 Monel at this stage in technology for the winner in the "best shaft material" race. It costs more than the other stainless types, is stronger, and is less subject to corrosion."
https://www.glen-l.com/weblettr/webl...propshaft.html

I considered using: silicon bronze, 630 stainless, monel (70% copper/30% nickel), nitronic 50/60, and even titanium. But I couldn't find matching fasteners in the same alloy for attaching the rudder to the shaft, which would have led to an even more serious galvanic couple than SS316L to the "bronze" rudder shoe. Is the rudder shoe also brass? I didn't see any pink in the shoe when I inspected it, so I suspect the shoe is really bronze.

So what I had before was a brass shaft coupled to a bronze shoe? That isn't much better galvanically than stainless to bronze. And still, it lasted 51 years. I'll have to tell my friends that a new shaft of titanium with matching fasteners and rudder shoe will be the perfect present for my 100th birthday (40 years from now).

P.S. The problem with bronze is - the only way to know it's true composition is to cut a piece off and send it to a lab for analysis. There are too many hucksters pawning off brass as bronze (like Bristol Bronze apparently did). The project already took 3 weeks longer than I'd planned - forcing me to sail back in winter seastate conditions. I sail my boat at least once a week - it's not a museum piece that I can take forever to restore.

[pbryant]

Doing a little more research...

My best guess (without a lab analysis) is that what I had before with the original rudder shaft was Admiralty Brass with a Silicon Bronze rudder shoe. On the galvanic scale* that would be:

60. Admiralty brass (rudder shaft), coupled to
70. Silicone Bronze 655 (rudder shoe)

What I have now is:

76. Stainless steel 316L (passive) (rudder shaft), coupled to
70. Silicone Bronze 655 (rudder shoe)

So 60 coupled to 70 is worse than 76 coupled to 70. The 316L shaft is closer on the galvanic scale than the original brass rudder shaft. The corrosion pattern is reversed - now the shoe has become the anode - but that can be mitigated with a sacrificial zinc anode.


*Reference: “Galvanic Series of Metals in Sea Water” from Army Missile Command Report RS-TR-67-11, "Practical Galvanic Series."

[ebb]

Bronze and stainless are often paired. Like turnbuckles, sleeve bearings.
And bronze propeller nuts on Aqualoy shafts.
The game changes IN sea water, which is a fine electrolite.
Stainless needs oxygen to be happy.
If you sail more than sit, moving water may be the solution!

Check the heel fitting socket as often as you can,
until you find the best way to zinc.


[A bronze bolt was added by thru-drilling the fitting to attach a zinc onto A338's heel fitting.....
and it did not seem to have worked at all. But it may have been a desperate and
too late fix by the DFO for damage that had already occured after the s.s shafted rudder
had been installed for some (unknown) amount of time. The boat, before I bought it,
lived in a marina but was often sailed and raced.
There was extensive corrosion to A338's heel fitting, even tho it was zinced. The stainless
rudder shaft showed no pitting or other corrosion. It was a rectangular fiberglass blade
with glass wrapped around the shaft. (In quiet salt water tests Aqualoy22 was completely
unaffected compared with 316 which suffered "random pitting and crevis corrosion."
http://www.wbmetals.com/shafting.asp)
At the time I thought the rudder shaft could be recycled propeller shaft (which if it was
Aqualoy22 has less carbon, much more manganese, chromium, nickle, molybdenum,
and nitrogen than 316 - and is also nearly twice as strong as 316. And corrosion free.)
Whether there is separation on the galvanicscale that would in salt water cause the
bronze heel fitting to anode to a stainless cathodic shaft is only a guess. However,
there was the result of the coupling I had to deal with. It meant having a new heel
fitting cast - and rebuilding the keel.]

.................................................. .................................................. .................................................. ...
316 vs 316L (www.engineersedge.com/) 316L considered a more weldable version of 316.
The difference is slight. I don't believe that passivation enters into the picture. Here is an explantion
posted by Juan Crawford:
"At welding temperatures, chromium carbides are formed in the molten pool.
The carbides are precipitated at the grain boundaries as the weld cools and solidifies,
resulting in a depletion of the corrosion-resisting chromium in these areas.
If a part is to be welded, reduced-carbon 316L will usually resilt in better corrosion resistance
in the weld area. If welding is not required, there is little if any difference in the corrosion
resistances of the two alloys."
316L does not have more chromium than 316 - only that carbon content is held to a certain level.
So it's a bit of a toss up.

[pbryant]

Ebb,

I really appreciate your advice on this. Unfortunately, the highly-recommended experts at Svedsen's had already replaced the bronze/brass rudder shaft with their recommended materials:
316 stainless shaft, and rebuilt the rudder including installing stainless fasteners into the rudder... before I saw you comments. What do you suggest now that "the horse is already out of the barn" besides zinc-ing the shoe?

[ebb]

Unfortunately the weight of my arguement was in prevention....
before I realized you are already committed to 316 for your rudder shaft.
Sorry, I should have changed the tone a bit.

I can imagine what the guys at Svendsen's might say to support their choice
of materials. 316L is very weldable, fairly easy to fabricate, and fairly resistant
to corrosion. Cheaper than bronze. And the guys are probably not Swedes!

Just have to keep an eye on the rudder system, every time you bottom paint
and change or rearrange the zincs. Also, it seems every location in a marina
is as different as every individual boat is when it comes to how susceptable your
boat is to corrosion. Maybe you'll have no problem.

Many boats have stainless steel rudder shafts.
Might ask Svendsen to recommend and install zinc protection for their installation.
They're the experts. No, really, they are!
In no way is Ebb an expert. There are real experts whose information and advice
can be trusted. They are far and few. So we have to take what we have and
deal with it. Even tho maybe it's biased, compromised, traditional, or plain BS.
.................................................. .................................................. .....................
Just bought some expensive strips of Hypalon (a polyethylene product) from McMasterCarr.
Complained that the black plastic/rubber had no markings on it. How do I kinow that
it is actually Hypalon and not EPDM (another polyehtylene)? Which it looks like, EXACTLY.
We'll give you a 'certificate of compliance'. OK, Thanks.
But how do YOU & I know that the unmarked sheet rubber is actually Hypalon
if it's not stamped or marked on the sheet?
No answer from McMasterCarr for that. But that is exactly the measure of trust needed
for a material (or by extension) work done: COMPLIANCE..... Leaves me feeling very
uncomfortable. Even though I mostly trust people I deal with, there are NO GUARANTEES!
And no expectations.