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Old 01-10-2009, 19:30   #1
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Converting to and Fabricating Bronze Chainplates / Tangs

Hello all,

I just spent a while searching through past posts concerning this, but have some more specific questions.


I have a 32' Westsail and would like to replace my 30+ year old stainless chainplates with bronze. Initially I planned to have PTF fabricate a set, but it is fairly cost prohibitive. Instead, I believe I can do it myself, but I would like a bit of help deciding on the particular alloy and form.

My current chainplates are 24"Lx2"Wx1/4"T 304 stainless, and boomkin/bowsprit tangs 16"x1 1/4"Wx1/4"T. Talking with PTF, they mentioned wanting to increase the thickness to account for bronze's lower tensile strength and to leave room for polishing; how much thicker is necessary? 5/16", 3/8"? 3/8" is the only bar I'm finding and that seems REALLY thick!

As for the actual fabrication: would I be better off trying to find strip in the correct width, or buying a sheet and having someone chop it with a torch? Most of my strips will need a slight bend - about 15deg; what is a good way to induce this bend? I have not worked with metal this thick before, but feel I should be able to do an acceptable job.

I know to stay away from "bronze" brasses, leaving phosphor, silicon and aluminum bronzes. Which is best and/or most practical for chainplate fabrication that is not on the waterline, keeping in mind that I don't have a whole machine shop.

Lastly, my current chainplates have square holes for the carriage bolts; I've read in many places to stay away from squares due to cracks forming at the corners. What is the best method for fastening the chainplates/tangs to the hull?


Thank you for your time!
Aaron N.
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Old 01-10-2009, 19:57   #2
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316 SS

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.
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Old 01-10-2009, 21:41   #3
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Sailmonkey,

Thanks for your feedback. I'd really like to go with bronze, but if it can't be had for a reasonable price, I'll likely go with stainless. Bud Taplin can supplies chainplates ready to install for $115/ea, which is reasonable considering the work that goes into them, but that makes for an $800+ project.

I had a quote from Atlas Metals today for $900 for a 24"x29" sheet of 3/8" silicon bronze. I'd have to cut, or have that cut to my strips, then do all the forming. Hopefully I'll be able to find a source for 2"W and 1 1/4" W bar in 3/8 or 5/16" thick.

Thanks for everyone's input!
Aaron
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Old 02-10-2009, 13:13   #4
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that $900 material price is what directed me to the $70 flatbar. Plus I was able to do all the work myself. I have no way of cutting a sheet of bronze in my garage.
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Old 02-10-2009, 14:27   #5
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Aaron,
Check out metal supermarket in tampa. They can get virtually anything. They cut my pieces to size for no extra charge. Their on distribution drive, behind Mahoneys marine supplies on Adamo drive
Steve
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Old 02-10-2009, 14:44   #6
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Manganese bronze would be good and is slightly stronger than Stainless. However I cant see it available in plate or flat bar. Bronze plate cant be flame cut (I dont think) and would have to be sheared. If you cant find approriate bronze in flat bar it's going to be a real problem. Silicon bronze is used in castings for boats some times. The sheared edge will be a mess and have stress risers as bad as the square holes. You would have to have it sheared and then milled along the edges and deburred to make nice chain plates. You could have them cast, but cast properties will require more thickness yet. For ease, especially on a Westsail you could go with all 3/8 thick.... All in all you better go with Stainless. Are yours actually bad? Wrought Bronze (sheet, bar) can be bent in a press brake or other press. You might get 15 degrees or so in a big vise... I would think that any bronze would be higher than stainless... bronze being about half copper....
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Old 02-10-2009, 14:56   #7
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Try: http://www.alaskancopper.com/pdf/ss/ss_flat.pdf for 316 stainless if you want to make your own. 3/8 x 2" 316 flat bar will weigh about 33 lbs for 12 ft. At $5 per pound (?) that's $165. If you can draw pictures they might quote making them for you. Do you know how to drill cut grind deburr this heavier stuff?
The square holes are a nice way to go for a nice clean look. When you think about it, the chain plate has nearly 3 times the crossectional area as the 1/2" pin of the turnbuckle... and how big is the tang on your mast at the other end?! so it is much lower stressed than much of the rest of the rigging.... Unless your chainplates are corroded.... dont put yourself through this mess and expense!
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Old 02-10-2009, 18:16   #8
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I have to agree with those recommending scratching the Bronze idea...I worked in a metal shop for a short stint and bronze is very labor intensive to work with...I think you will find yourself upside down quickly cost wise going this route...You said yourself yours have lasted 30+ years...how long are you going to own this boat?

Up-size the stainless one size if you need to feel more comfortable and be done with it.
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Old 02-10-2009, 19:26   #9
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I love the idea of bronze chainplates, but so far found only two places where they could be had - NZ and UK - probably they simply have some old supplies because of the extent to which bronze was used there up till the 60-70ties.

I like the way bronze works and ages - showing places of too much stress before they become problems. The SS just bang-cracks and the story is mostly over.

Still, if you are not in one of those places blessed with availability of marine bronze you may be forced to use SS, which is anyway an excellent choice for the application.

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Old 02-10-2009, 19:32   #10
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Hey all,

Thank you all for your comments. Steve, I'll check out the source in Tampa.

I probably do not "need" to replace my chainplates as the rig is still standing, but there are two visible cracks on two chainplates, and my current tangs all have fissures. So for my own piece of mind, I want to replace them.

My reason for wanting bronze is multifaceted. I realize my current chainplates have worked for a while, but my boat hasn't seen serious cruising and weather in fifteen years. It seems that most sailors replace stainless that is 20+ years old before doing anything long distance with it. The reason is that stainless corrodes from the inside, oxygen-starved side out, so you don't see problems until they are dangerous.

That said, I am willing to make my chainplates from stainless if I am unable to find bronze for a reasonable price. If I do use stainless, I would likely go with 316 and increase from 1/4" to 5/16" thick. Would this be an adequate increase in thickness?

Thank you!
Aaron
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Old 02-10-2009, 22:38   #11
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I disagree..you NEED to if you can see cracks

FWIW..you will gain nearly 30% more strength just in that one size jump...It should be plenty strong.
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Old 03-10-2009, 17:15   #12
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Stilltraining,

Yes, I know I need to replace them. That was my bit of subtle humor as visible crack is the last-draw for stainless.

I'm going to check into pricing of 5/16" 316 stainless.

Thanks all!
Aaron
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Old 05-10-2009, 21:07   #13
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Hello all,

onlinemetals.com offers Aluminum Bronze, alloy C95400, in 3/8"x2" and 1.5". The total cost for all of the bronze I need (12ft of 2", 6ft of 1.5") would be about $300.

I have seen people say that aluminum nickle bronze and silicon bronze are good choices for use around the water. However, I'm not sure about "aluminum bronze". It's specifications are thus:

Aluminum Bronze, C954 Minimum Properties Ultimate Tensile Strength, psi 85,000 Yield Strength, psi 32,000 Elongation in 2" 12% Brinell Hardness 170 Chemistry Copper (Cu) 83.0% min Iron (Fe) 3.0 - 5.0% Aluminum (Al) 10.0 - 11.5%

As opposed to silicon bronze:

Silicon Bronze, C655 Minimum Properties Ultimate Tensile Strength, psi 85,000 Yield Strength, psi 55,000 Elongation in 2" 20% Rockwell Hardness B90 Chemistry Copper (Cu) 97.0% min Iron (Fe) 0.8% max Manganese (Mn) 1.5% max Nickel (Ni) 0.6% max Lead (Pb) 0.5% max Silicon (Si) 2.8 - 3.8% Zinc (Zn) 1.5% max

Does anyone have experience using aluminum bronze; I want to make sure it is a strong enough metal. I'm not sure if "32,000 psi" for yield strength is enough compared to silicon bronze's "55,000 psi".

Thank you for your time!
Aaron
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Old 06-10-2009, 00:01   #14
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Boy now your going to get me lying to ya.. HA!

All I remember is There are a Zillion combinations of Bronze...Every manufacturer has their own twist and sales pitch as to why theirs is better for your application just like Gasoline Companies.

Aluminum and Silicon Bronze will differ in what portions of what is all in them...Aluminum bronze still usually has some silicon in it just not some other harder stuff so it is easier to shape or bend. Those PSI numbers mean that a 1 square inch bar of the stuff will fail at 85,000 pounds of pull..it will start to deform at 32,000 pounds of force and not return to its original shape and it is going to stretch or elongate 12% before it fails in a straight line at its 85,000 pound failing point.

That's about all I can remember and I might not be 100% at that..HA!..Sorry .....It is less corrosion resistant though how much i have no clue.

So how much does your shroud tension exert..?? couple 2-3-4 thousand maybe..catch my drift.. You will have to do the math on bar width and thickness to compute a translation...ie,,1/2 bar 2" wide will give same results so 3/8 will be what???...

And now the fun stuff...drill a hole in it and pull on a smaller cross section and what do you have???..More needed brain power then i'v got ..thats what you have..HA!
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Old 06-10-2009, 00:47   #15
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Just for grins I went and looked up 316 SS..its 40,000 / 22,000 and 15%
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