bronze composition

naval bronze (brass) 464
% 60 - copper
39.25 - zinc
.75 - tin

manganese bronze 675
% 58.50 - copper
39.25 - zinc
1 - tin
.25 - manganese
1 - iron

everdur 655
% 95.8 - copper
3.1 - silicon
1 - manganese

These alloys come in hard and soft versions.
ANY bronze alloy with over 25% zinc is subject to dezincification. (actual fact)

Which of these bronzes are subject to dezincing?

Three guesses.


IMCO, modern marinas will dezinc anything.
Marinas in the '60s were not hot like they are today. Agree?
Galvanic corrosion can potentially affect any metal immersed in an electrolyte. Alloys with tin make them particularly strong and corrsion resistent. Above the waterline. Strive to keep all metals in the water the same alloy. Shaft, shoe, rod, bolts, pins, thru hulls. Put sacrificial zincs everywhere.

I'm thinking about making a rudder shoe out of some inert waterproof material(StarBoard, PVC, Delrin, Nylon) and buying a little piece of bronze to machine a bushing in which the rudder post will pivot. One of them will become sacrificial.

I think I would rather replace the rudder shoe than the rudder post.

So, if I go to the bronze gettin' place and ask for an alloy just ever so slightly less noble than the rudder shaft(naval bronze), what would I ask for?

You know, THAT is not a bad idea!!!
If you keep the mass of the original, why wouldn't it work?

Delrin or nylon could be the first choice if you can get a chunk of single dimension. And machine it down. PVC would alow you to 'glue' the shoe on with epoxy or rubber. Starboard is polyethylene and may be too soft to take the thru fastenings. Never know. Delrin is hard stuff, of course.

Glass reinforced nylon (Marelon) if you find chunks, might even be the best stuff. Anything with carbon in it you couldn't use because of the bronze shaft.

Great idea, should follow thru on it!!
All the plastics you mention come in reinforced versions. Don't know about poly ethylene/propylene.

ebb

Thanks for the, as ususal, well thought out response.

What alloy of bronze would you use for the bushing? The local bronze seller suggested aluminum bronze.

In a stock -from the factory- A/C is what % of the rudder weight is carried in the shoe? If all, do you think it has remain so or could some be shifted above to the top of the rudder shaft log? If so the material of which the rudder shoe is constructed could be less structural.

Thanks

Jim

You know me. I would use the same alloy as the bushing. Close isn't close enough. Ask your expert if he knows what galvanic corrosion is, yes? - then will he guarantee the installation?

It isn't usual to have a bushing down there on the shoe. If the hole is drilled precisely 3/4s inch diameter and 3/4s inch deep and the shaft end is repeated exactly, minus a micron, you have, I believe, and Pearson certainly believed,
a good long lasting fit. If one has to have a bushing, I would think a thin washer of delrin would be ok. If you make the strap gudgeon openable as part of your yearly maintenance, a new washer could be slipped in fairly easy. You'ld have to disassemble the tiller head.

I'ld guess that ANY thin material you'ld be putting down there would have to be renewed regularly.

The socketed rudder shaft in the hole has no place to go. Can't hardly move downward. Might argue that it can't even wear any if it is fit to the specs. I know in my bones that the married couple have to be totally compatible, preferably the same stock. Otherwise they will be exchanging electrons not vows :D


[You know I don't think a bushing is necessary or even an upgrade. If you keep the specs as above, the bearing surface of the added bushing would be too small, too narrow to act as a 'bushing'.
(If you turned the shaft down to 1/2" you could make a quarter inch washer for the shaft for more surface for the flange to sit on. I can't see that a smaller stub on the end of a 1" shaft is a good thing on the barn door type of rudder we have.)
The 3/4" shaft end turns only on its circumferance in the bottom of the ideal hole right where the drillpoint's V shape begins. Ideally the shaft here shares support with the flange that rests on the shoe. In an ideal world the shoe has exactly the correct machined surface at exactly 90 degrees to the shaft. But this is probably more luck than reality. Would think that the heel and the shaft being a quarter of a degree out a washer/bushing would be reduced quickly to useless. Arguable that this may be a reason for the added piece.
IMCO such a small inconsistency mates in to something very stable because of the relative softness of the copper alloy. IE the rudder shaft stabilizes itself. (Such closeness demands exact same alloy in the two parts!!!) The shoe is itself the bushing with not much friction at all.]

[2) Agree that a bushing is a sleeve that lines a hole? So that's the arguement, that the hole in the heel of the shoe is self bushed. And works in this case because it is, or should be, the same alloy.

However, when you talk with an engineer you might be designing in a bushing in the glass reinforced plastic shoe for the rudder shaft to turn in. It would keep the hole from elongating. I think all the polys (carbonate - ethylene - propylene - etc) are too soft and won't be made hard by the fiber. There are a zillion plastics. At the moment that Marelon stuff is unbelievably tough and hard and proven in the marine env. It might be comparable to bronze, maybe. And it might be found by another name if the patent has run its course.]
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later Edit: If anyone persues an alternative non-metal material for the rudder shoe...GAROLITE (available at McMasterCarr.com) would certainly
be a phenolic/glass contender as the substitute. The mass of the existing cast rudder shoe would translate, imco, to an equal mass
of G-10 - and is a much harder material than nylon or acetal.