silicone braunze chainplaites

[brian A.]

Hi, My name is Brian and I have a 1968 cascade 30' fiberglass sloop. The stainless chainplaites are in need or replacing. I wonder if anyone has experience using braunz? The plates will be mounted on the outside of the hull and throughbolted with backingplaites. I'd like to use braunz for a couple of reasons, one the material is relatively easy to shape. I wonder if anyone has a better idea of what are its physical properties and how much larger braunz chainplates will need to be relative to stainless. I suppose the bigger the better. how does 1.5"x1/4" and maybe weld a couple of short 1/16"x1.5" at the eye for extra support. I don't know if it's the purist in me but part of me sides with braunz, It seems to me to be a softer material and therfore will flex a little more when put under strain.

[Noah]

I have bronze chainplates on my Nordic Folkboat. They are almost the exact size that you descibe. About 1.5" X 1/4" and 18" long. They are fastened with bronze bolts. You are correct about there being some bend to the plate. It doesn't take too much work to put a slight curve into it. They have proved plenty stong in the first 50 years of my boat's life, so hopefully they will keep that way.

Noah

[paladin]

Brian......
if you put a doubler at the top of the chainplate, after ascertaining the correct size for your application, bevel the outer edge of the chainplate and the doubler and fill with weld/braze...DO NOT weld ACROSS the chainplate as the heat may actually weaken the metal. Also...if you have a choice, punch the holes through the metal...as opposed to drilling....

[Mike Field]

Nothing technical to add to Noah's or Chuck's comments, Brian, but welcome to the Forum. Please stay and contribute -- it's the experience of so many different folks from so many different backgrounds and with so many different boats that makes this such a great place.

[Art Read]

Chuck... Punch instead of drill? To avoid heat buildup? How exactly do you "punch" through 1/4" silicon bronze? Clueless about metalworking here....

[plimsol]

Bronze chainplates will be just fine. The PIRATE just had hers replaced - 1.5 x 24 x 1/4.
Sil Bronze will bend with a little work and will conform to the shape if backed and bolted. The bolt holes were drilled without difficulty. The old chain plates were 75 years old and still functional, but worn.
When you order the chain plates have them cut not sheared. We had the chain plates sheared for a six metre, ERICA, and the sheering will cause the strips to twist, which requires extra work to straighten.
It you are in the Puget Sound area, Alaska Copper and Brass has Sil Bronze in stock and will cut to size.

[paladin]

Art......under some really neat instruments you can see the stress lines created in the metal by the drilling...punching alleviates that and actually hardenes the metal around the hole...I made my chainplates...and those on Jim Brown's Scrimshaw at Western Electric in Oklahoma City in between vacations in Vietnam. They had the tooling to punch large pieces of metal...and a lab and some neat folks that enlightened me to the difference....Western Electric (the manuf. of the telephone switch gear) garaunteed the frames for 40 years...some are still functioning after 80 years.......

[PugetSound]

Some points about how bronze behaves that may clear up some of the comments made above:

- bronze will work harden. Beat on it enough and it will harden locally. That local area will also increase slightly in ultimate strength but it will do this at the expense of ductility.

- bronze is heat treated differently from steel. Most people know that if you heat steel red hot then plunge it into cold water you'll temper it; do this with bronze and you get the opposite result (you will anneal it - also know for relieving entrained stress).

- bronze will, if not machined properly (i.e. drilling) smear. When metal alloys smear the crystaline structure becomes compromised and, in addition to entrained stresses (which can warp the metal), there is an increased likelyhood of crevice corrosion and de-alloying occuring. Other alloys are also know to be sensitive to machining technique - particularly titanium alloys (all titanium on the markey is an alloy, usually with aluminum).

I would recommend that you, at least, consult a Machinery Handbook before attempting to fabricate something in bronze (check with a local college engineering library since these handbooks are expensive). It is far too beautiful a metal to be wasted.