Stainless with Bronze in Salt Water

My new-to-me 1982 Marine Trader DC has a hodgepodge of stainless metal combined with Bronze. For example-the PO had the prop shaft tunnel pipe replaced with 316 stainless pipe. Its screwed into bronze stuffing box one end and bronze cutlass bearing fitting on the other end , the packing bronze fitting is held together with 2 stainless bolts, the swim platform is held by bronze fittings with stainless steel pipes 45 degrees at the hull-- they usually are underwater, the seacocks are bronze with stainless steel bolts holding them to the hull. Oh yes -the rudder is stainless steel with a bronze packing fitted into a mild steel structural fitting. This long time sailor asks: Is this typical in the Trawler world?? Thanks anyone

Many early TT (and lots of later) ones were put together with what was on hand at the local hardware store..

Except for some commercial fish boats , boating was illegal in that era so a knowledge base did not exist , and cost was always a factor.

Up grading with silicon bronze bolts , etc, is what most owners have done over the past 20-40 years.

The stainless steel prop tube and cutlass and shaft log replacements was done by Marsh Harbor Boat Works in SC. The PO said the stern cutlass brg holder "somehow came loose" and wore a hole in the original fiberglass prop tube holder. I suspect the brg holder "came loose" due to a ss bolt or bolts holding the cutlass bearing breaking due to being weakened by electrolysis.

I had SS rudders, SS shafts, and basically all else was SB or manganese bronze u/w. Boat was 24/7/12 in the warm salt. The issues i did see were with the small SS screws holding shaft logs in, and the garboard fitting. Here, both SS crevice corrosion was at work, along with some galvanics that slowly dissolved some SS screw heads. Also saw some pitting corrosion on the shaft at the stuffing. All this stuff was years and years in the making, and not a huge issue, overall.

One problem with SS set screws and bolts, the commonly available grade is 304 which is less resistant to chloride corrosion than 316. The latter grade is available from McMaster Carr or other big industrial houses. The problem with "bronze" in today's market is it pretty much all comes from China, and might be called "silicon bronze" or "manganese bronze" when it isn't really. It takes a laser spectrometer to be able to tell for sure. Cutlass bearing bodies aren't even claimed to be bronze, but rather brass. If you keep zincs on everything in good shape, galvanic corrosion should be minimized, replacing the 304 SS with 316 will help with crevice corrosion but not eliminate it.

Good boat yards aught to have one of these, which I had my company buy:
https://www.thermofisher.com/order/catalog/product/XL2

Takes about 15 seconds to get a non-destructive good read on aluminum, steel, copper alloys, much more.

Very popular with scrap metal yards.

diver dave said:

Good boat yards aught to have one of these, which I had my company buy:
https://www.thermofisher.com/order/catalog/product/XL2

Takes about 15 seconds to get a non-destructive good read on aluminum, steel, copper alloys, much more.

Very popular with scrap metal yards.

Click to expand...

From the website's "Request a Quote" form, it looks like it takes a bit of unobtainium to purchase one of these analyzers.

Arent there a few bronzes that have common names that include brass?

Like Naval Brass and Red Brass that are also known as bronze and formulated to avoid dezincafication?

AKFish said:

From the website's "Request a Quote" form, it looks like it takes a bit of unobtainium to purchase one of these analyzers.

Click to expand...

I recall about $10k or so; 4 years ago.

psneeld said:

Arent there a few bronzes that have common names that include brass?

Like Naval Brass and Red Brass that are also known as bronze and formulated to avoid dezincafication?

Click to expand...

"naval" about 39% zinc. "red" takes Zn down to about 15%.

I can send an excel via email upon request. I have tensile strength, and composition for a number of marine alloys, including Al, and steel, etc. But, I do notice some pretty small elements added can make some big physical changes. For instance, the 1 to 4% of silicon added to pure copper (to make silicon bronze) makes its electrical conductivity 10 to 15 x worse.

"Bronze" is a very slippery word today. It used to mean tin and copper alloyed perhaps with a few other things to improve strength. There are lots of things called bronze that aren't these days. Add to that the stuff being sold specifically as silicon bronze that isn't.

The laser spectrographs are a really neat tool, but a bit out of the impulse buy price point. It would be interesting to wonder down the isle a the local West Marine and shoot some of the "bronze" fittings and hardware. I keep looking for a cheap used one on ebay, no luck yet.

Naval Brass refers to a copper alloy of around 59% Copper 40% Zinc and 1% Tin with a trace amount of Lead. This alloy falls into the subfamily for Brasses known as Alpha Beta or Duplex Brasses. These Alpha Beta Brasses are generally harder and stronger than other non-Alpha Beta Brasses.

As its name implies, Naval Brass was originally developed for sea water service applications. Tin in included in the alloy composition in order to improve the corrosion resistance of Naval Brass. The presence of lead in Naval Brass assists in the machinability of the metal. C464 Naval Brass Rod has a fair machinability with about 35% of Free Machining Brass.

The addition of Tin also gives Naval Brass a high resistance to dezincification. Dezincification is a type of dealloying in which one of the constitutes of an alloy is removed by corrosion. Dezincification was first recognized as a serious problem in brass tubes used for ship condensers around 1920. At the time this problem was referred to as “Condenseritis”. Since then various alloys have been formulated to stop this process, one of which being Naval
Brass.

Http://www.nationalbronze.com/News/what-is-naval-brass/

Both California and the EU now are putting up a fuss with lead in anything, even when alloyed. We have had to deal with Al without copper, and brass without lead for a multitude of products for a couple years now.
Nickel is a now a target too.

DDW; that tool I referenced has an X ray source for the exciter. We also have a FTIR, which uses, I believe, a small IR laser source. That we use for elastomeric/plastic/rubber analysis.