Converting to and Fabricating Bronze Chainplates / Tangs

[Cheechako]

304 and 316 Stainless should have a yield strength of about 40,000 psi. So you are loosing about 20% strength there. However if you are going with 3/8 thick compared with 5/16 Stainless you are gaining about 16% back. I'm not sure what Alum Bronze is. There doesnt appear to be any Nickel in it so it's not what's normally called "aluminum nickel bronze". Try to track down it's chemical resistance etc. Maybe ask them for the technical specifications on it. It appears to be 83% copper so it's got a lot more copper in it than like manganese bronze.... 12% elongation isnt much. The other mystery is how it can have 32KSI Yield and 85KSI tensile strength but only 12% elongation...? Most annealed stainless steels should have roughly 30% elongation.
Doing some research it does seem to mentioned for Marine use. It appears to be a casting alloy though....? This might be the reason for the minimal elaongation. You might ask if the bar is Wrought or Cast.. I also found this:
This alloy is produced by a process called "continuous casting" whereby the molten metal is cooled almost to hardening, then continually pushed through a shaped die to harden into its final shape. This means that the dimensions of the bars and tubes produced in this alloy are oversize, and their surface finish is very rough.

[blahman]

All,

I spoke with Pete out at PTF today and he assisted me in understanding the alloys. Basically, the cast alloys with high corrosion resistance are fine choices for chainplates, so aluminum bronze, aluminum nickle bronze; things in the C95XXX range. The trouble with these bronzes is that they are very hard, inelastic, strong metals, so working with them is trouble. Fabricating using silicon or manganese (wrought) bronze is much easier for its elasticity and bendability; it can be cold worked.

Most of PTFs castings are C955 or C954, aluminum nickle bronze or aluminum bronze. If they are going to be working a piece, they cast it of silicon bronze to enable easier working.

So the 3/8" aluminum bronze stock will work great, the trouble will be bending it. It can't just be put in a hydraulic press as it'll crack or shear; it has to be heated. I didn't ask him about the procedure for heating and working with the metal as that's his trade! I'm going to dig on the internet to see what I can learn and then decide whether or not I'll by the stock and make the chainplates.

Chainplates from PTF would be $180/ea, plus $100 for bending, plus $150 or drilling. Boomkin and bowsprit whisker tangs would be $90/ea. So I'm going to check into working the metal myself and doing it for $300 total.


Thank you all for your time!
Aaron N.

[Cheechako]

You may find that you only need to bend 10-15 degrees and may be able to do that with those alloys anyway. Drilling holes in bronze is tricky, drills love to suddenly stick and break. A power feed drill press would be preferable, but at any rate, you will want to get your rpm just right and then feed accordingly. If you are talking $250 for bending and drilling them all I would definitely go for that.....

[DaveC]

If you used bronze, are you worried about electrolysis with your stainless steel rigging wire? Perhaps you'd have to put a zinc on each of your stays/shrouds to prevent then from corroding against the bronze chain plates, especially if they take shots of salt water regularly?

Just a thought,

-Dave

[Fishman_Tx]

Originally Posted by Sailmonkey

I just replaced all my chainplates with 316SS. The original 304SS lasted 32 years so I should be doing better than that with the 316. I though about bronze also but it came down to knowing what stainless to use, and not even being able to find the correct bronze that I could afford. The whole project cost $70 for the flatbar, $50 for the drill bits, $10 for cutoff wheels for the grinder. I did the drilling with a $100 northern tool drill press. I also used the drill press to spin the polishing wheel.

where'd you get your flatbar? I'm gonna be down shortly and would like to pick some up. Our chainplates are one-sided (exposed not encapsulated) with bolts thru the plates then the knees with nuts and washers only. i'm making backing plates.

[Oceansandmts]

Must be only youngsters on this board.

The appropriate alloy of bronze used to be the metal of choice for yacht fittings. Lasts forever in salt water, no crevice corrosion and has other benefits like easy to make castings, and, pertinent to this discussion, easy to machine. I used a lot of bronze on my build, you can cut it with a band saw, it is easy to drill and tap (doesn't work harden like stainless) and from long experience (not just mine) it has no problems being in contact with stainless above the waterline (or below, where you might want a zinc). You can substitute silicone bronze fasteners for stainless size for size, it is at least as strong. Another benefit is no galling of fasteners like you occasionally get with stainless.

Don't just take my word for it (after all, I could be just another internet wannabe with no knowledge and time on my hands) check out builders like Herreshoff, Nevins and Casey who built many high end wooden boats with all bronze fittings and fasteners. If the boats are still around, the fittings are still good. Or call Bristol Bronze and talk to Roger, he will give you an earfull on the benefits of bronze.

If you use stainless you should passivate and polish, with bronze it doesn't matter. Builders stopped using a lot of it because it doesn't look as good unless chrome plated (then it looks better) and, it is definitely more expensive. I happen to like the look of aged bronze, and I like not having to worry about "stainless" corrosion.

I would use round holes if you use stainless, you could use button head cap bolts for a look that is about as smooth as carriage bolts. Available at McMaster Carr. I have seen chainplates for carriage bolts with square holes where the corners are slightly rounded, I would think this would be better if you do want to use carriage bolts. I don't have a lot of experience with square vs rounded holes except for aluminum masts where sharp corners are definitely a no-no.

$800 for a complete set of bronze chainplates is not a bad price, they will look nice on the Westsail and last forever. How many more years do you plan to sail the boat?

[motion30]

Originally Posted by Cheechako

You may find that you only need to bend 10-15 degrees and may be able to do that with those alloys anyway. Drilling holes in bronze is tricky, drills love to suddenly stick and break. A power feed drill press would be preferable, but at any rate, you will want to get your rpm just right and then feed accordingly. If you are talking $250 for bending and drilling them all I would definitely go for that.....

There is a trick to drilling bronze that involves grinding the edge from the drill bit so it will not grab

[blahman]

To update you all,

I went ahead and purchased the aluminum bronze stock to fabricate my own chainplates. Total cost for the material was $280, so we'll see how it goes. The metal will be here this Monday, and I'll give feedback and photos on how it goes.

Any last minute advice on drilling or working with it? C954.

Cheers!
Aaron N.

[Fishman_Tx]

Still waiting to see where in Houston Sailmonkey found that 316SS flatbar on the cheap..

[blahman]

Hey all,

Just wanted to let you know that I wound up using the 3/8" Aluminum Bronze to fabricate my chainplates and it was a breeze. Took maybe four or five hours to do all ten, including polishing. The material is very strong and makes the boat look much better, I think!

You can see all the photos of our ongoing renovation at:

Deck Renovation/Rerigging

There is also a photo of the chainplates attached to this message.

Thanks for your help!
Aaron N.

[seandepagnier]

Did you manage to bend the aluminum bronze with success? I am replacing my chainplates, and after reading this thread I will get aluminum bronze. I need a bend in fore and aft chainplates

I wanted silicon bronze but I can't find anywhere that will sell it in chainplate dimensions, I can only find it in round bar.

[wolfenzee]

When I said I was going to replace mt chain plates (30yo+ SS) someone said "If it ain't broke don't fix it", my return was, "I'd rather replace my chainplates ,than mast later. Useually there are only two ways to tell if stainless needs replacing x-ray it or if it fails (cracks count as a partial failure)> I am going to replace my chain plates with bronze bar.

[memelet]

Originally Posted by wolfenzee

I am going to replace my chain plates with bronze bar.

Did you consider titanium?

[wolfenzee]

Originally Posted by memelet

Did you consider titanium?

As my boat is a heavy displacement ocean cruiser the savings in weight would be less significant to me than it would be to an anal racer.
I have three sets of chain plates, each about 24" long, when the boat was built galvanized were used, which were changed over to stainless about 30 years ago.

[Matt sachs]

I just bought 2 inch flat SS316 stock 3/8 inch. I paid $7 a foot. As far as working it, use the correct drill bit, go slow, flood it with coolent and it works fairly easy. The 15* bend shouldnt be a problem with an anvil and a strap of leather to protect the finish. (or a press) Getting the holes drilled in the right place to match the hull might be the hardest part of the job.
I love the look in post #25 great job. It looks like it matches the rest of the rigging better that the SS would have.