Zinc plates?

[Lance Dean]

I always have many interesting points/questions that arise from reading books.  I wish I'd write them down as I can never remember them later.

Here's something I came across recently from "Clear the Bridge!" by O'Kane - the Tang had just come in for a refit after her 4th war patrol:

...Our zincs were another matter.  These plates, about six inches wide, a foot long, and a half inch thick, were secured with cap screws to the struts, propeller shafting, and the area around the stern tubes.  Without them, the electrolytic action between the bronze propellers and the steel hull would erode and pit the structures about Tang's stern.  Higher on the atomic scale, the zincs went into solution first.  Ours were gone, so the docking was necessary if for this reason alone...

I had never thought about this before.  Can you imagine what would happen to museum boats IF they were allowed to keep their original propellers and were moored in salt water?

[JTheotonio]

We used a lot of zinc chromate-based paints.  Today we'd have to put on special suits just to use this stuff.  Back in time they just gave is a big wide brush and said go to it kid!

[Paul Farace]

Scarificial zincs... COD's are still in very nice shape, thankyou! Even after 55 years without any renewal.  Ofcourse, some of our stern plating is going away  .

These rectangular blocks are everywhere aboard the boats, from inside the freeflooding areas in the superstructure, to the struts of the props. And yes, the idea is that they go before the boat does. There are even long rods, think about 4 feet long and about 5 inches in diameter, with a cable in the middle, like a corndog on a stick. These were hung along the sides and ends of the boats.  They pit badly and look like whiteish concrete after exposure. 

Funny thing, several of our WWII subvets were using one of these cylinder zincs to hold up the 300-lb torpedo loading hatch on deck!  The original steel pipe with T-top was missing (since replicated)... but when I saw that basically life and limb were being safeguarded by a plaster-of-Paris pole, I had to point out the folly... they had no idea of what the thing was and thought it was "concrete."  When they laid it down on the deck, it broke in two!   

You will also find such zincs on bridges, piers, anything that comes into contact with water that might be subjected to bimetallic corrosion or galvanic action.