July 2006 Issue
PS Advisor: 07/06
Stainless vs. Bronze
Whenever I buy new fittings (like cleats, blocks, fairleads, etc.), I never know whether to buy stainless or bronze. We have an old Bayfield 32 (built in Canada, where we’re from) and a powerboat my wife and I use for fishing. Now that we’re in Florida, the corrosion is just terrible. Do you have an opinion about stainless vs. bronze?
You sent PS running to some metallurgists and to books like “Metal Corrosion in Boats” by British engineer Nigel Warren; “Boatowners Mechanical and Electrical Manual” by a trusted old friend named Nigel Calder; and to our 25th edition of the engineers’ best friend, “Machinery’s Handbook.”
First, stainless steel is misnamed. It’s not stainless and it’s not corrosion-proof. (Many of the almost countless varieties suffer from crevice corrosion, which is insidious.) Some of the better grades of stainless come pretty close to lasting forever, but it is always amusing to see a manufacturer brag that a piece of hardware is made of 304 stainless, which is not nearly as good in seawater as 316.
Copper and nickel-based alloys have for centuries been preferred for underwater use. Bronze is copper based, though its composition can vary. Good bronze contains no zinc; brass does. Brass is far inferior to marine-grade bronze.
Bronze actually can be made stronger than stainless steel. In its hundreds of forms, bronze is made by alloying copper elements with—to name a few—aluminum, beryllium, cobalt, manganese, nickel, silicon, and lead. The latter is added to improve the workability of the bronze.
Good stainless is OK for deck fittings and gear not immersed in seawater. Stainless needs oxygen. Never paint it or cover it tightly.
For a workhorse metal that’s affordable, any of the dozens of varieties of good bronze come the closest to “forever.” PS welcomes readers’ views on this subject.
I have a Jeanneau 43 that came with the wound steel standing rigging tightly wrapped from the deck fitting up to about 8 feet with PVC tubing. Does this jeopardize the stainless steel? Should it be removed?
Newport Beach, Calif.
To answer this question, PS turned to yacht builder, racer, and former Tartan project engineer Bill Seifert, who also authored “Offshore Sailing: 200 Essential Passagemaking Tips.” Here’s what he had to say.
“When stainless steel is deprived of oxygen, it is subject to crevice corrosion. This is the reason why the International Sailing Federation (ISAF) now requires that lifelines NOT be PVC coated.”
Talk to your boat manufacturer and ask their intended purpose of coating the standing rigging. If for chafe protection for the genoa, loose-fitting shroud rollers would be our choice. If you’re on a tight budget, make your own rollers by choosing a SS washer with an ID just over that of the shroud wire, and an OD just over that of the smallest ID plastic pipe through which the standing rigging swage fitting will pass. Make a cut in the washer from OD to ID.
Make the plastic pipe to be a few feet higher than the genoa clew (6 to 10 feet). Disconnect standing rigging, slide on plastic pipe, and use pliers to twist the washer to go around standing rigging wire above the swage, then re-twist to make it flat. The washer will keep the plastic pipe from sliding down.