Corrosion

[Arminius]

Just some trivia. Whenever two dissimilar metal components of your boat are in saltwater, corrosion will damage the one that is located lower on the following list from Wikipedia:
"Galvanic series (most noble at top)
The following is the galvanic series for stagnant seawater.

• Graphite
• Palladium
• Platinum
• Gold
• Silver
• Titanium
• Stainless steel 316 (passive)
• Stainless Steel 304 (passive)
• Silicon bronze
• Stainless Steel 316 (active)
• Monel 400
• Phosphor bronze
• Admiralty brass
• Cupronickel
• Molybdenum
• Red brass
• Brass plating
• Yellow brass
• Naval brass 464
• Uranium 8% Mo
• Niobium 1% Zr
• Tungsten
• Tin
• Lead
• Stainless Steel 304 (active)
• Tantalum
• Chromium plating
• Nickel (passive)
• Copper
• Nickel (active)
• Cast iron
• Steel
• Indium
• Aluminum
• Uranium (pure)
• Cadmium
• Beryllium
• Zinc
• Magnesium"

 

[Lazy Daze]

Arminius, galvanic corrosion will happen not only in saltwater, but in freshwater, too. It even happens just in "air" - in any place where there is an electrolytic solution (moisture). The amount and type of moisture... temperature... it all comes into play.

 

[Arminius]

An anecdote: Pinhole leaks would develop about every 6 months in basement overhead copper pipes. I would hear the dreaded dripping noise and get at the pipe with minimum ceiling removal. Then I would hire a local kid and remove and replace the pinholed section and seek expert advice such as "apprentice plumbers didn't wipe acid flux off" or "bad batch of pipe." Eventually I called the re-pipers and got a bid on the whole house-not good! Had a heart to heart with the estimator and he suspected galvanic action. Then I remembered my old failed project to run hot water to the hot tub using galvanized pipe which was still attached. I would have had to set the water heater temp too high for the water to water heat exchanger in the tub to have worked and I balked at the added complexity of a mixing valve for the domestic side.
So I removed the old non-functioning galvanized pipe and have never had a pinhole leak in my pipes since. The general area where the pinholing occurred was not really close to where the old galvanized pipe jury rig tied in to the copper pipes.
I brought this subject up when a poster wondered why we have SS props.

 

[Henry Boyd]

Thirty years in the current house and never a leaking copper water pipe. The house we briefly owned in California with steel piping, a freaking plumbing horror show.

 

[Arminius]

Thought I would check those ring washers in the lower drive unit as I replaced the impeller last fall. I've now convinced myself that small mistakes could matter and I got the book. These washers are supposed to be stainless which is mildly attracted to a magnet, if at all. One of the existing washers snapped to a magnet so I walked over to ACE and found a bin of them. Unfortunately, they also failed the magnet test so I hunted some more. For a Gen 2, Alpha 1, the long 1/2" bolt securing the round zinc/trim tab gets no washer, the short 9/16th" bolt revealed by removal of that zinc gets a SS ring washer and the two 7/16th" inch bolts securing the flat zinc in front also get SS ring washers.