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Marine Metal Detector
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Lin and I were recently at the Pacific Sail Expo (Oakland, California boat show) doing seminars
and introducing our new book.* One of our quests at the show was a new
galley stove. The burners on the "all stainless steel: stove we bought fifteen years ago were
rusted badly. Our search for replacements came up against "sorry no parts available."
Serendipity struck. Just as I was about to begin my search, I noticed the Sail Logo refrigerator
magnets being handed out. They would be just the thing I needed to act as an iron/steel detector
as we shopped. We'd used one 35 years before when we were building Seraffyn. Suppliers were
amazed when the pocket metal detector stuck to a steel spring in an all bronze hatch dog, or a
steel screw in a stainless steel hose clamp.
A small magnet will also indicate different magnetic attractions between different types of stainless
steel. Series 302 or 304 stainless has a bit of attraction, enough to support the weight of a small
magnet (1/4" by 1/23" by 1" or refrigerator door magnet size). Series 316 stainless has only a slight
or no attraction.
Over the Years I have noticed that wherever two slightly different alloys of stainless steel touch each
other there is a tendency for one or the other to rust. I've also seen serious pitting in this situation.
Testing each item you plan to buy with a "Marine Metal detector" could help you spot these metal differences
before they cause problems. (A tip for those who get bleeding or rust marks running down their hull where
stainless bolts go through stainless steel fittings - use a silicon bronze bolt or screw in the stainless
steel fitting. (See diagram) There will be no more bleeding and there will be no electrolysis if the fitting
is above the waterline. In fact it is common practice to use bronze turnbuckles with stainless steel wire for rigging.
There is a down side to everything. Remember this pocket sized "marine metal detector" could demagnetize your
credit cards so they refuse to work at the ATM. That could leave you saying "Damn, no greenbacks to buy that
bronze bilge pump with the tempting 25% cash discount."
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Diagram - Marine Metal Detector
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| Silicon Bronze is similar in tensile strength to stainless steel aluminum bronze, is stronger, and could be used in high stress situations - such as for back stay chain plate bolts on the transom. The green bolt heads look a lot better than rust rivers down the hull in my opinion. |
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* "Cost Conscious Cruiser" - Paradise Cay Publications 1-800-736-4509
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