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Shop Brass Damaged the Clipper Ship

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Bob Salter
User Rank
Iron
Re: Small component, big damage
Bob Salter   4/12/2012 9:06:14 AM
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My experience with the American Brass & Bronze industry has not impressed me with their quality and ethics. The bearing manufacturing I work for purchases a lot of Centrifugally Cast Bronze for bearing cages. This is preferred because centrifugally cast alloys claim "wrought" strength properties that are higher than simply cast versions. When a rash of cage structural failures occurred, we had the remains analyzed for chemistry and structure, both of which turned out "acceptable." We decided to order a few large blanks from which "dog bone" tensile specimans could be machined and tested. Ultimate (tensile) strength came back somewhat lower than claimed, so we filed a complaint with the supplier. Their response was that their product was not deficient because the industry specification that they follow allows them to keep trying new test speicmens until they obtain a group that passes. (The industry writes its own specs.) In the end we resolved ourselves to an addage frequently heard in old Western movies, "Yes, we know the game is crooked, but it's the only game in town."

Tool_maker
User Rank
Platinum
Owning a Yacht
Tool_maker   4/16/2012 12:42:00 PM
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This whole thread makes me feel good that I can only afford a Fish & Ski rather than such a fancy rig as this. My main corrosion problem is rusty fish hooks on favorite plugs and they are easy to replace.

 

dbues
User Rank
Gold
Re: Small component, big damage
dbues   4/23/2012 8:14:30 PM
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Interesting deductions, but this failure was in 1974 after owning the boat for only 6 years. 

Through-hull fittings, seacocks, propellers, and shafts are all commodity products, whereas the forestay fittings were made at the factory. 

Stray current corrosion can occur on any metal.  This is what occurs when your shore-power cord is plugged in at all times.  ESPECIALLY if some joker connects the white neutral (current-carrying conductor) to the green safety ground. 

GALVANIC corrosion is due to dissimilar metals immersed in an electrolyte.  This is where the "de-zincification" can eat you alive.

Many alloys contain a little zinc (<5%), but when the content approaches 25-35% the de-zincification can weaken the material to the consistency of a sponge.

 

dbues
User Rank
Gold
Re: Small component, big damage
dbues   4/23/2012 8:22:52 PM
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I owned a 1967 Broadwater power boat from 1992 to 1996.  I always swam around the boat once after dropping the anchor to see if there were any loose screws.  They were built with brass screws (mostly). 

In fact, they had one barrel of bronze screws at the factory in Mayo, MD, for when the Marine Surveyor came by (they hid the brass screws and rolled out the barrel of bronze ones when he was there).

I can somewhat sympatize, since the bronze screws were much softer and it was easier to strip out the phillips screw head. 

When we owned a 1966 Pacemaker in 1977, I noticed that MANY of the screw heads were stripped when they tried to drive screws into the oak frames.

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