Don, please use the search button at the top of the page and type in "outboard." You will find extensive discussions on the subject. Bottom line, the 4 cycle 8hp Nissan, Yamaha, Mercury, etc (all built by Tohatsu) seems to be the consensus choice.
Any other questions? Please use the search button first!
Hello Jim,
There are some 400 series stainless steels that don't corrode in salt water. The best of the more common 300s is 316. Even that will corrode when oxygen deprived like under washers or where tight against something like under the keel. Sometimes stress corrosion happens when a fastening or plate is under load, screws or bolts crumble or the fitting will develop cracks where corrosion begins. Only low carbon 316 should be welded, normal 316 will rust immediately at the weld.
Is that cup welded on the skeg in your pic? Whether something stainless will corrode is unpredictable, sometimes it won't, even tho it should. Water running by a rudder shoe provides oxygen which may help the fitting survive longer. Out of the water s.s. creates a thin passive protective film in the presense of oxygen.
Stainless has its own problems under water by itself, unless an electrical contact with an annode is constant it will always corrode. In the presense of bronze (copper doesn't like to change its voltage, so when a current happens to it, it is the likely one to corrode or cause the corrosion depending on what it's coupling with) the galvanic corrosion is again unpredictable.
On 338, which had a brass shoe with a s.s. rudder shaft in it, it was the shoe that experienced the worst of the pitting. One would think the copper alloy more noble, except the brasses called bronzes have a load of zinc and lead alloyed in them. If an alloy is a little bit off, and the electric current is just so, I guess the alloy itself can corrode. The s.s rudder shaft in this case showed no obvious deterioration. It was not zinced - the shoe was.
Two very different alloys: s.s and bronze have absolutely no business together under water. That is asking for trouble.
Maybe to say they will create some bad business together. Since you can't isolate rudder shaft and shoe you have to zinc the separate pieces. But either the zincs wouldn't work or they'ld dissolve so fast the shoe or the rudder would quickly become unprotected. Even similar alloys (two bronzes or or two stainless) are different enough to begin exchanging little particles.
Last edited by ebb; 01-03-2005 at 11:39 AM.
ebb
Thanks for the educated reply. The piece in the pic looks like two different diameters of pipe welded to a piece of flat stock.
It came from a very old Pearson someone cut up. I have no idea if it was oringinal or a replacement. If a replacement, of course I don't know how long it spent in the water but it shows no sign of corrosion.
That said, nor have I seen the effect it had on it's partner the rudder post.
Dissimilar metals are always a problem I guess and welds are a problem. I have seen that on the 100% stainless holding tank on my old Cheoy Lee.
It is unlikely that someone is going to say, "Sure! No Problem! Let it rip!" but I thought I'd try.
You mentioned that even different batches of the same alloys can be a problem. Does anyone know how the people who are selling Bronze Silicon shoes are insuring compatibility with the rudder post?
Wow! It's after 5:00 on New Years Eve. The shadow is on the Yard Arm. The heck with cathades and anodes and all their unfaithful little electrons!!
Time to be happy!!!!
Thanks for the advice in this and the other conversations.
HAPPY NEW YEAR
JIm
HNY Jim,
Play around with the Search option on the top of this page. There are shoes being made. (But I must say I disagree completely with the alloy.) I've seen very rare mentions of alloys having to be the same. It is my opinion that the shoe and the shaft MUST be the same alloy. Even so you have to trust the supplier, who I would actually ask for the alloy percentages even where they originate.
Personally I chose what I consider one of the purest Bronzes available, a real bronze, not a brass masquerading as a bronze they sell to the pleasure boat crowd. Everdur 655. Almost pure copper + a pinch of silicon. Manganese bronze is nearly 40% zinc. In the iffy environment of salt water, hot marinas and no positive way to protect metal, that has too much of a spread. For me. It's a fine strong alloy for stem fittings, chain plates and the like.
I would mate the M. bronze shoe with the same in rod for the shaft. But then what will you use to hold the rudder planks? Could thread smaller rod to make the 'bolts.' Could be done avoiding ubiquitous silicon fasteners available almost everywhere. Ah, yer thru hulls are another unrelated brass called bronze. My Everdur cost like gold. Don't think M.B is cheaper, don't know, tho.
HNY Jim,
Play around with the Search option on the top of this page. There are shoes being made. (But I must say I disagree completely with the alloy.) I've seen very rare mentions of alloys having to be the same. It is my opinion that the shoe and the shaft MUST be the same alloy. Even then you have to trust the supplier, who I would actually ask for the alloy percentages and the three digit numeber you can look up. What country the alloy originates may also be a clue as to its purity.
Personally. For 338's rudder and shoe I chose what I consider one of the purest Bronzes available, a real bronze, not a brass masquerading as a bronze they sell to the pleasure boat crowd. Everdur 655. It is a classic marine bronze. Considered propeller shafting. Almost pure copper, a teaspoon of silicon and a pinch of manganese. Manganese bronze is nearly 40% zinc. In the iffy environment of salt water, hot marinas and no positive way to protect metal, that has too much of a spread. It is for me. It's a fine strong alloy for stem fittings, chain plates and the like. I am not a metalurgist or an engineer. There is very good reason to believe that the original Pearson Ariel rudder shoe was/is manganese bronze.
I would mate the M. bronze shoe with the same in rod for the shaft. But then what will you use to hold the rudder planks? Could thread smaller rod to make the 'bolts.' Could be done avoiding ubiquitous silicon fasteners available almost everywhere. Ah, yer thru hulls are another unrelated brass called bronze. My Everdur cost like gold. Don't think 675 is cheaper, don't know, tho.
[Let me add that 655 can be welded. M. Bronze (675), being a brass, can only be brazed. If you are going to make the two-part shaft original rudder with the bent upper portion that goes over the aperture, you can cold bend the 1" silicon bronze ( but it will work harden if you bang it too much) Wouldn't try - I'ld take it to a metal shop with drawings! Really don't know if 675 can be bent or threaded.]
If I became edjercated it was self defense. Too many amateurs and professionals too are influenced by tradition, the marketplace, and experts influenced by tradition, industry brochures & spec sheets, and the mktplace.
But if I get on a cruiser site and the guy is unhappy with some stainless or badmouths some big name bilge pumps - and is specific about it - I'll give it a listen and look for confirmation. Figure their lives depend on their boats and gear. The ONLY metal you should go into the low latitudes with is silicon bronze. Only the very best 316 will last 2, 5, 10 years. None of it under water.
It would be hard to imagine that Pearson skeg you have to be original. Another clue is that the fastenings are not in sheer when attached to the keel. To do that the shoe would have to have sides. like a shoe, and be thru fastened thru the keel molding. I don't trust people like me who talk too much either.
Last edited by ebb; 01-09-2005 at 04:48 PM.
dezincification
One simple statement.
The reason you have corrosion or dezincification in the shaft or other rudder part, or if you have pitting in the shoe,
is because there is ZINC in your bronze alloy.
Tell me I'm wrong, ok?
Here is the shoe you need
FRED POMERANZ
1168 QUEETS DR.
FOX ISLAND, WA 98333
ebb & Bill
Thanks for the terriffic information. You both put a lot of effort into this board and I appreciate it.
On C-80 the rudder shaft looks fine. But the shoe is almost totally gone.
Obviously the shaft is more noble. I wonder what alloy of Bronze the original shaft is?
I am working on a solution to this common problem. What alloy would be most like it but slightly less noble?
How often would you say the average person hauls their boat to do the bottom?
Bill: If you get this post, I was interested in the finished rudder shoe you posted back in 2005 with a nice picture. I am not sure how to use this forum since I am a new user. I do not know how to reply directly to you or simply put up a new post, so here it goes.
Is it still available in finished form? Would it fit an Alberg 35? Where can I get it? If Fred Pomeranz, do you have his email address? Carl291 may have an unfinished one to sell, and I am waiting to hear more from him. Thanks for any assistance you can provide. George
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