Rust stains from stainless steel?

[mick]

I have replaced all the steel fittings on my transom with A4 stainless steel from Sea-Screw because I was fed up with rusty streaks spoiling the look of the boat. I am still getting these streaks from some of the new bolts/washers on the backstay fitting. Any idea of what is causing this? I assumed A4 stainless would solve the problem.
Thanks in advance.

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[Col]

Try sealing threads with silicone sealant first.

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[maxi]

May sound silly, but make a careful check to see if you have any electrical voltage in your rigging. If you have an electrical leak into the rig this will almost certainly cause rust to leach out of exposed fittings. A radio aerial connected to the rig would be a good place to start.

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[mick]

How do I do that?

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[maxi]

Re: how?

With a multimeter, set on the lowest voltage setting, connect between your suspect fittings and the water. You may find a very low reading, but any voltage at all will track down to the water, paticularly when the hull is damp - taking some of your stainless steel with it.
If you do find a voltage, it's a tedious process isolating each part of your electrical system, one by one, until you find the culprit.
Strange though it may seem, this is a far from uncommon situation.

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[richardandtracy]

Stainless can be triggered into two states, active & passive. When passive it won't rust, when active it will.

You will need to break the electrolysis cell somehow. My suggestion would be to disassemble the rusty bits and plaster lanolin on the offending items before re-assembly.

If there are stray currents around, then something else will start to rust though. On that happy thought...

Regards

Richard


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[Evadne]

Another cause of rust stains from stainless steel is crevice corrosion. It sounds unlikely in your case if the fittings are all above the waterline though. (It happens during constant contact with trapped or stagnant sea water that creates the anoxic conditions required, which is why s/s bolts underwater can be a problem unless you gunge up the threads with silastic to keep them dry.)

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