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gaffney1951
03-18-2009, 12:55 PM
"I'am replacing the deck in my 86' 230 scorpion. After removing the old deck I removed the foam around the sides of the tank (70gal) all of the side surfaces are in pristine condition. I then cut a 4" hole at the fuel pickup location so I could check the condition of the interior all looked very good with the exception of two very small pits at the aft bottum area of the tank. I then fabricated an alum. cover drilled and taped the tank and used brass screws to secure the gasketed cover to the tank. The top of the tank had some very mild corrosion so I sanded the top of the tank and applied a coat rustoleum primer for rusty surfaces (tank was originally painted grey) and was going to top coat it with rustoleum enamel. Now I'am wondering if this primer has any metal in it, and if it could be problematic re galvanic corrosion. I also bought two small Zinc annoids that I was going to attach to the two vertical tabs on the tank. Any thoughts or suggestions much appreciated. Thanks, Mike"

sandkicker
03-20-2009, 11:06 AM
"Brass screws are never a good idea anywhere on a boat. Brass is a copper/zinc alloy.
Copper anything near aluminum is also never a good idea in a boat...so bronze screws (copper/tin) are also a bad idea. So, if screw you must, use aluminum screws.

Most corrosion on aluminum tanks is caused by "crevice corrosion"

http://www.bertram31.com/proj/tips/fuel_tank.htm ("]http://en.wikipedia.org/wiki/Crevice_corrosion[/url]

For the best writeup I've seen on aluminum tanks in boats...go to:

[url=")

There was also a good writeup for non foamed intanks on the Bayliner site (at one time?)"

sandkicker
03-27-2009, 09:23 AM
RE: "also bought two small Zinc annoids that I was going to attach to the two vertical tabs on the tank"...

Zinc anodes only work
1) Item is immersd in water
2) Zincs also immersed.

They need to be in the "conduction path" of the electron flow induced by dissimular metals or stray electrical currents.

They aren't a talisman that wards off corrosion.