Brass and bronze are two different things. Brass is an alloy of copper and zinc. Bronze is usually an alloy of copper and tin -- although there are also aluminum bronzes, manganese bronzes, and silicon bronzes, which are alloys of copper with aluminum, manganese, or silicon, respectively. Each of these catagories (brass, bronze, aluminum bronze, etc.) includes many different alloys with different properties.
I'm not quite sure what "shop brass" is, but cheap screw machined parts are often made out of free-machining brass (UNS C36000). This is an alloy of copper, zinc, and lead. The lead helps to make it readily machinable.
As the article correctly points out, copper and zinc are very far apart in the galvanic series, so when a brass part is exposed to a good electrolyte (like seawater), the zinc acts as a sacrificial anode for the copper. Ultimately, all of the zinc dissolves out of the brass, leaving a spongy mass of copper with very little strength. I'm willing to bet that if your uncle looked at the failed part under a microscope, he would have seen this sponge-like structure. This process is called dezincification.
Naval brass is a type of brass (usually approximately 60% copper, 40% zinc) which also contains a small amount (0.5 - 0.8%) of tin. Small amounts of arsenic, phosphorus, or antimony might also be added. The presence of these elements help to inhibit dezinicification.
The absolute best copper alloys for saltwater service are copper-nickel alloys. These alloys have excellent corrosion resistance. However, they also tend to be fairly expensive.
This article is a good example of why proper materials selection is so important. It pays to do your homework -- or, better still, ask a metallurgist.
Bob from Maine, it sounds like you'[re suggesting this may not be a Made by Monkeys problem but rather a simple wear-and-tear-over-many-years problem. Are there ways to check this before it causes a serious accident?
Don't know how long you'd had this boat, but Cheoy Lee Clippers were made in the 50's and 60's, so this incident could be due to simple age. My experience with Cheoy Lee has been their hardware is of very high quality and their hulls of that era were quite over-built. Most "Bonze" shafts, propellors, seacocks, and general fittings have some zinc, though I can't remember the exact percentage. Boats that spend time at the dock, particularly where other boats have shore-power plugged-in have a tendancy to de-zinc many of their bronze underwater fittings due to stray eddy current in the water. Also the Dolphin Striker assembly is usually not disassembled during winter storage so is never checked and unfortunately is a fairly common point of failure for this reason.
Andrew Morris designed a circuit that could detect a stroke victim's groan and convert the sound into a signal so caregivers would know when help was needed.
New disc magnet motors fit into the design trend of stepping up to closed loop performance while maintaining the cost advantage of stepper motor technology.
At the Design News webinar on June 27, learn all about aluminum extrusion: designing the right shape so it costs the least, is simplest to manufacture, and best fits the application's structural requirements.
On April 21, NASA launched a novel project, putting into orbit three satellites that employ an off-the-shelf commercial smartphone as the control system.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 5
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For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.
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