Silicon Bronze vs Brass

[flydog]

I am building a 12' daysailer (first build). The plans call for silicon bronze plating for the spar top and the tiller. Would brass plate be acceptable? I only plan to use this boat in fresh water.

Happy New Year everyone!

flydog

[LP]

Flydog,
I finished a 16' wooden daysailer about 4 seasons ago. I used an extensive amount of of brass in it's for it's hardware. Outhaul bracket on the boom, chain plates, bitts, hardware up at the hounds, and the horse. I also use a fair amount of bronze in the construction. Gooseneck, chocks, cranse iron, pintles and gudgeons, and screws for structural attachments and bronze hardware.

My plans called for the use of stainless steel, but the design of the boat was traditional looking so I wanted to enhance the it further along those lines.

First, if you use brass, make sure it's equivalent in strenght.

Second and the biggest concern with using brass is a chemical process called dezincification. The process is usually associated with another process called electrolysis where where stray electrical currents (generally associated with eletrical systems) will steal less-noble metals(i.e.zinc) from components. Brass is primarily zinc, I think.

That's the short story. If you opt to use brass, use it in locations that are easily inspected and check them on a regular basis. I'd suggest using bronze in locations that are inaccessible. Don't use sainless steel screws with brass.

I haven't had any problems, so far. The boat will be going into it's fourth season in the spring and it lives in the garage when not in use, so it's led a short and protected life. I normally sail freshwater, but I have taken it down to Galveston several times. It's amazing how fast the saltwater tarnishes the bronze and brass, but no ill effects.

I'm not in a position to tell you it's ok. That has to be your call. So far it has worked for me.

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You could google dezincification, electrolysis, and galvanic corrosion to get a better idea of what you are dealing with.
This link might be useful,

http://www.classicmarine.co.uk/Articles/metals.htm

[PAR]

Bronze and brass are made of the same materials, brass being a copper/zinc alloy with some tin and/or lead tossed in to improve hardness, color and machining qualities. Bronze is an alloy of copper and tin with zinc tossed in to increase fusibility.

Regular brass (hardware store stuff) is typically 65% copper, 35% zinc, machines well, but is relatively weak and easily fatigued. Naval brass (60% copper, 1% tin, 39% zinc) has much better strength and machining.

Bronze comes in all sorts of mixes, most are strong (far stronger then brass) and ductile. Bronze needs to be matched with the machining requirements for the particular piece. A few examples would be a cast ship's bell (75% copper, 25% tin) which is quite stiff, but not too strong having little to no machining requirement. On the other hand a forged stemhead fitting (85% copper, 10% tin, 5% zinc) very strong, well machined, hard metal.

In your case, the two pieces suggested in the plans are to protect the spar and tiller from moisture ingress and UV damage. Paint will work, but metal works better, IF it's kept well bedded and clean. Use the brass and put a clear coating of your favorite mixture on it to keep it shinny if you like. Always use fasteners of similar or compatible material. Brass for brass in this case.

[Raggi_Thor]

Can it be that we simply call it copper? Like "copper nails". But we really mean bronze with 85% copper, 10% tin, 5% zinc or similar?

[marshmat]

Well, I wouldn't think so, Raggi- the properties are just so different. Even within things called 'bronze' there is an enormous range of materials with completely different properties.
The changes in a material due to even tiny amounts of other elements can be huge. The conductivity of a piece of silicon, for instance, changes by many orders of magnitude when you replace one out of every million silicon atoms with an aluminum atom. Compare 6061 and 6063 aluminum alloys- a few more grams of magnesium and a few grams less of copper in a tonne of metal, and the tensile properties change by more than 30%.
My point is, as far as Flydog's boat is concerned- make sure you know the actual grade of the metal you're getting, because general groups like "brass" or "stainless steel" include such a variety of materials that you should look up the particular type and grade you're planning to use.

[TerryKing]

Hey, Matt and PAR (others too) we could use some help with:
http://www.boatdesign.net/wiki/MaterialsForBoatbuilding
in the Wiki. You will see a vast wasteland in the METAL area, just waiting for you to get bored. Please collect a little of the metal wisdom you have shared on this and other posts, and plunk it in there! Thanks...

[marshmat]

Thanks for providing more sources of procrastination, Terry Being bored seems to be happening a lot more often than usual lately. Something about the term being (nearly) over.
I know I haven't been around here much lately- that may change, it is now exam season and I suspect I will be looking for every distraction I can find I'll help with that Wiki when I get a chance.

[tylerars24]

Does anyone know of a website that carries a good selection of brass blocks and other rigging hardware?

[Mac Attack]

Brass has no business being on a boat, anywhere, period!

[timgoz]

I nice laquered brass oil lamp gives a warm glow to a cabin at night. But in any mechanical situation I agree with Mac.

Tim

[lazeyjack]

Originally Posted by Mac Attack

Brass has no business being on a boat, anywhere, period!

he is quite right, there is absolutely no comparison, , brass will quickly fall to bits as a fastener in salt, uses only for ornemants and interior screws\
despite all the googled stuff here, what you need look for is tensile strength in any structural fastening or member, tables of which can be found in most books or Googled, brass has the tensile of a hard cheese) some of your ss screws from Taiwan not much better, just wind off even with a small screwdriver, let alone a dc drill the toughest are nickel alloy bronze, merrimen bronze, quality USA ss, trouble is you ask the supplier what is the tensile , and these days you get a vacant blank idiotic stare