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I will be getting a new rudder shoe cast in the not to distant future and am seeking input on manganese versus silicone bronze. From other postings and my limited knowledge of metallurgy I'm initially inclined towards manganese but am open to suggestion. Anyone care to venture an opinion one way or another? Thanks.
Well...I don't know which one is what, but I asked my chum the Naval Architect...he said that if one gets too specific it just opens bigger cans of worms a lot of times in these situations with ever-expanding choices, but that if one tells the foundry you want "Naval Bronze" they will know what you want and give it to you without introducing complicated choices...for whatever that's worth.
Let me know how much for a pair of 'em?
Dave
Naval bronze it is. If it's silicone bronze and lasts 50 years it will outlast me anyhow.
I'll make plaster molds of the shoe when I get it and find out what it will cost to have them poured if you still are in need.
Thanks,
Tom
I sure could use a new shoe toooooo....
Capt willie,
I cannot use the private message option because it has a 500 character limitation that includes your message. I find it frustrating and stupid.
OK. I built up 338s corroded rudder shoe with bondo to my reading of the specs in the Manual. Corroded in place where the zincs were
attached(!) and also involved straightening one of the flanges that had been bent because of the tightening of bolts Had it cast locally in silicon bronze.
The end of the keel crumbled when the shoe was taken off because it was solid polyester with no fiberglass in it. One inner bolt held the shoe on. A DFO had also remounted the shoe slightly further aft. It was a mess with too many holes. So it was rebuilt with a couple of silicon bronze spikes vertically up into the good stuff. And I used the new shoe to mold a new end of epoxy and chopped strand to the keel over the ends of the spikes. Mocked up a dowel shaft so that it centered in the rudder tube and had the same standoff from the keel top to bottom. Easy to do when wet because slight adjustments can be made before clamping or propping. Used a scew bottle jack.
BUT it turned out the new shoe was a bit larger than the old one, in relatiuon to the existing keel). Using a long batten, on one side, the 'flat' part of the keel forward of the rudder post was kindof hollow.... The other bowed a bit, and I couldn't stand it. Now both sides are faired out at least 3/16" back to the rudder post. Now, it's at least 1 3/4"-2"wide the whole end of the keel where the rudder swings. The shoe fairs into the keel so you hardly notice.
Turned out (that my interpretation of) the shoe from the Manual translated on to 338 was wider than what 338 had befor. Fairing it to the keel is maybe too much for a normal refit. However, if you are interested:
The model is heavy because the old one is inside. But it is delicate and still covered with the foundary's graffite used to make the sand mold. You're welcome to borrow it, I'll UPS it to the foundry of your choice, if you promise to ship it back!
First, check, get some measurements with outside calipers to see if it has an acceptable fit your boat. The model is 3 1/4 inches OA across the flanges on the forward end - 2 3/4" inside. And about 2 1/8" - 1 5/8" inside - at the aft end where the fitting is solid and slanted to take the rudder shaft. This casting model is an even 1/4" thick all round.
Have to drill the bearing hole yourself, which will require a tricky jig to hold it for the drillpress. I spent a lot of time making sure the hole was exactly centered. And the holes thru the side are your choice, but the 4-pin pattern is in the Manual. I had a machine shop drill the 3/4" x 3/4" deep hole where, precisely as I could, using the 6' mock shaft dowel (to locate exactly where the ruddershoe was originally : see page 171 in the Manual), traced it on the flat. Flat required no clean-up or machining.
It's for sure the same size inside as the original, right there inside the original model.
Hope this is useful.
My opinion is that you should match alloys with shaft and shoe. Manganese and naval brass are close on the galvanic scale. But I really would argue NOW that they present a problem when matched with silicon bronze. That includes any fastenings you will put with the shaft or fitting. I think the can of worms applies to mixing alloys. Even bronzes. I want to hear exactly what any metalurgist has to say on this.
338's shoe was quite corroded, and it may have been that if the alloy was manganese, it was 40% zinc. Bristol Bronze said it was manganese bronze which is highly resistant to salt water corrosion. But obviously NOT in all cases. DFO has an entirely different rudder in place of the original, that had a stainless shaft. Believe it reacted with the rudder shoe, despite, or because of the zincs. Or forgetting about them. Manganese bronze cannot be considered an underwater bronze like silicon, because in an electrolyte like salt water it can self distruct by galvanic action.
I went with silicon because silicon fastenings and rod are common. I went with silicon because it is mostly copper. And I thought the active bearing surfaces of shaft and shoe should be the same metal. If the boat is going to be parked in a marina where strange electric currents abound it is something to consider. Under water, manganese bronze (brass) fittings can self destruct in modern marinas.
Another possibility is to go and buy a suitable sized chunk of bronze and have someone make the part on a milling machine.
While I'm very keen on getting the plaster cast from the new cast shoe, and while I would go for 2 of them if someone cast a batch real soon, I'm probably going to end up doing that. The biggest "ouch" is gonna be the cost of the materials, I think.
The mill work is really straightforward, so a person could probably get it done by a student at a local technical college for very little...I've done that before for things, and my advice is to speak with the instructor and have him choose the student! Also, a lot of people in this world have mill skills and have the machines in their garage, especially hot-rodders and motorsport types. I have a couple of guys to choose from who are both good friends and treat me pretty right.
Really complex things, or things that need to duplicate existing parts (like mast shoes, masthead fittings, spreader sockets...) are much more easily done on modern CNC gear that incorporates a stylus-type plotting machine. This lets the operator make a digital "map" of the original part, then clean it up and alter as needed into a finished program. The technology department at the local University here has that stuff, and I am presently trying to cultivate a capable student there. Lot of times, a case of good beer can buy a lot of machine labor!
On that topic, I am going to be having a couple sets of billet spreader bases made within the next few months. The Ariel ones are same as the Triton as far as my experience at least...if anyone is interested, please let me know. I'll also be having a pair of mast shoes and a pair of mastheads done...by the look of things in the manual, we also share the same spar dimensions (in section) and the same type wood step, so those should probably work, too. The main thing for me is buying the appropriate alloy stock and finding the right student, beyond that I'm willing to have the fellow do more than just the two sets of parts if I can know ahead and get all the mat'l in one shot, and have the parts all made at once.
Dave
So how do I go about matching the alloys of the shaft with a new shoe? I have a suspicion that the rudder is not origional--it's in good shape, appears to be fiberglass, and tapered at trailing edge very thin. And the top bearing and fitting have no play.
My thoughts right now are I'm gonna be in fresh water--
Columbia River--so it might not matter much. But as far as resale down the road when the kids are bigger and we need more room, it would be nice to do the job right.
Need to do some history checking on the boat I guess. Anyone know anything about #350 from Friday Harbor Washington?
Capt Bill,
Like I said, it's my opinion. Somebody should be pointing out that it's going to take yea many years to show corrosion with the bronzes. Ten, fifteen, twenty, and the underwater circumstances.
If you are in fresh water it's probably forever.:D
Ebb,
You really eased my mind with your last statement!
Jim