Brass sterntube and sea water

[Graham_Wright]

I ordered a stern tube from a long-established marine engineers specialising in diesel conversions and associated gear.
When it arrived, it seemed to me to be produced from brass. My engineering colleagues agreed and when I contacted the supplier, I was told "Yes, its mde from CZ121 (i.e. ordinary brass) which everyone uses now". Protesting that brass and seawater are a disastrous mix, I was told that phosphor bronze was far too expensive.
I contacted their material supplier who I also use and ordered cored phosphor bronze and made my own stern tube.
The material was more expensive;- £1.00!

Any comments?

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[cliff]

CZ121 Pb3 is the most commonly used alloy for high-speed machining. Has limited cold ductility but can be knurled. It is not suitable for use in a salt water environment

Dezincification Resistant Brass

In certain circumstances where water supplies are unusually aggressive, conventional duplex brass water fittings can suffer a form of corrosion known as dezincification. This involves selective leaching of the zinc which can cause fracture of the fitting. As previously mentioned, dezincification resistant brass, CZ132 (CuZn36Pb2As), should then be specified. This is made as fittings, stopcocks and valves with a carefully controlled composition by extrusion or hot stamping followed by heat treatment to ensure that the material will satisfy the requirements of the standard dezincification resistance test.

Brasses For Service In Seawater

The small additions of tin in Naval brass and Admiralty brass improve the corrosion resistance in seawater. Naval brass, CZ112, contains 60% Cu, 39% Zn and 1% Sn. It is a duplex brass and is therefore harder and stronger, but less ductile than Admiralty brass, CZ111, which contains 71% Cu 28%Zn with 1% Sn and is an alpha brass. Neither of these alloys has a direct equivalent in the proposed BS EN Standards. The nearest equivalent to Naval brass is a leaded alloy CuZn38Sn1Pb, (CW712R). Nowadays aluminium brass CuZn20Al2As (CZ110) has replaced admiralty brass for tubes for marine service, but admiralty brass continues to be used for fresh water. It should be noted that the alumina film which forms on aluminium brass will prevent wetting by solder so aluminium-free alloys must be chosen if soldering is required.

Dezincification resistant brass and some high tensile brasses can also be used for marine applications.


Brasses For Architectural Applications

Brasses containing aluminium or manganese are frequently used for architectural applications because of the self-healing, attractive surface films which they exhibit. Manganese brass CuZn40Mn1Pb1 (CZ136) has a chocolate coloured film when oxidised and the aluminium-containing brasses which are included in BS2874 as CZ130 have a bright yellow colour with a silvery sheen. Both types of alloy have excellent hot workability which allows the complex section shapes required in many architectural applications to be produced. Other attractive colours are available with the use of the gilding metals, CuZn10 (CZ 101), CuZn15 (CZ102) and CuZn20 (CZ103) available as extruded sections, rolled sheet and strip and as tube.


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[macd]

"long-established marine engineers". Who, pray tell.

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[Graham_Wright]

Give me a ring (01531 821 673) and I'll tell you !

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[Graham_Wright]

That was a fvey informative response;- thank you.

I used SAE660 (aleaded bronze) for my own manufacture.

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[Graham_Wright]

and that was an interesting way to spell "very"!

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[boatmike]

A very sad story. Even sadder that the company tried to bulls**t their way through by saying everyone uses free machining brass (CZ121). As Cliff rightly says it is not suitable at all. Can't see why you won't name and shame the manufacturers as they can't sue you for telling the truth. Others should know to avoid them. I guess the lesson is always specify EXACTLY what you want in writing when placing the order and get a fixed price quote before hand.

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[silverseal]

If a long established supplier of marine equipment supplies materials that are patently unsuitable for a marine environment, then whom are we to trust. Clearly some members know precisely what materials to specifiy, but surely normal yachtees, rely on the good reputation of long established suppliers. You must name the supplier, so that others are forewarned!

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[BrendanS]

In more detail here
<A target="_blank" HREF=http://www.severnmetals.co.uk/notes_br.htm>http://www.severnmetals.co.uk/notes_br.htm</A>

<hr width=100% size=1>Me transmitte sursum, caledoni

 

[Graham_Wright]

T Norris

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[dickh]

Aren't T N****** based in Norwich, Norfolk and probably supply most of the Broads boats - who are usually in fresh water? Maybe this explains their use of brass......

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Graham_Wright]

No, Isleworth

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