Marinette Boat Forum

Just having bottom job, starting with sandblasting to bare aluminum.

Is it best to apply anodes when the hull is bare, before any paint is applied?

If so, what protects the hull surface under the anodes? Is it just natural Al oxidation? What keeps the hull from pitting under the anodes, esp in salt or brackish water?

Any advice is greatly appreciated!

Thx,
Jeff (not fast)

Jcbwell wrote:Is it best to apply anodes when the hull is bare, before any paint is applied? If so, what protects the hull surface under the anodes? Is it just natural Al oxidation? What keeps the hull from pitting under the anodes, esp in salt or brackish water?

Sandblast the surface beneath the anodes. Then tape them off when you paint. Attach anodes when painting is complete. Anodes should be over bare metal otherwise their protective ability is compromised. The anodes themselves will protect those bare metal patches. Use stainless steel bolts to attach them snugly. Open to discussion here is something I recall from years earlier about using thick washers under the bolts so there is actually some space between the anodes and hulls. I forget the details -- someone else will have to chime in here.

The hull should be clean under the old anodes, so I just leave them on and blast and paint over them. Then remove them and put the new ones on. I put grey zinc anti-seize on the back and on the bolts for better contact and so they come off easier. Buy Aluminum anodes from Boatzincs.com They are so smart you can call them and just tell them "37 foot Marinette". They will know just what you need. Best prices too.--Ed

JR, you confirmed what I thought was the case. Just seeking confirmation to be sure.

Seems thick washers on the outside of anodes would keep them on longer as they erode.putting washers between anode & hull seems like a very bad idea.

Thanks again!
Jeff (not fast)

Busia,

Have always bought from boatzincs. Good folks.

Would discourage using zinc anything with this system of protection. Will form a galvanic cell and increase erosion. You might get by with this in real cold water, tho.

I used stainless washers on each bolt head and nut... All aluminum anodes on the hull.

I wish I had used a premium caulk around the edge of all my anodes. I think that would keep the mating surface clean for better protection. I haven't read of anyone else doing this. I will do it on my next anode change.

I pulled the anodes I put on last year, and the backs look like a white crystalline material has grown. I've been in brackish water on the ICW, so prob aluminum chloride.

Can't be good for conduction, but Capac still read OK.

Thinking about putting SST washers on, so drill holes dont erode and hurt conduction or loses anodes prematurely.

Also found one, 6" anode per rudder not enough, so making it two, 6" per rudder.

My annual Anode maintenance here on Lake Michigan is removal from keel, trim tabs and prop shafts. The bedding areas are all cleaned with a fine emery scotchbrite flapper wheel to remove the white deposits and provide a clean surface. The anodes are cleaned, with a belt sander held in a vise, to remove build up. I use 3 different grit emery belts from coarse to fine. The shaft andoes, camps, are cleaned and the halves weighed to balance within tenth of a gram. The mounting stainless steel nuts, bolts and star washers are cleaned by a quick bath in limeaway. Every few seasons I replace the hardware that fastens the zinc to the keel. I replace the anode strips every 6 to 7 years and shaft zincs every 3 to 4 years depending on their appearance and wear from the annual belt sanding.

The cleaned parts are reinstalled and each season my Capac here in the lake starts the season at 0.95 and may drop to .09 by end of the season by cleaning and using 5 feet of zinc on each side of the keel, 1 foot strips on the trim tabs and 1 shaft zinc on each shaft for this 1990 32' express.

May seem a little extreme but small effort to keep her solid.

BTW there are no anodes on my rudders, I replaced the stock ones with a pair I had fabricated out of Stainless Steel a dozen years ago.

Here's something I used to do with keel & trim tab zincs: when they were almost half worn, I put them aside and replaced with fresh ones. When the fresh ones wore almost to the halfway point, I would clean them and mount the cleaned old ones -- sort of double zincs -- along with the recently worn zincs. Helped cut the expense of anode replacement and glad to report in 17 yrs of owning that boat, there weren't any corrosion issues except at the deck rail attachment points. That problem was attacked by providing better water drainage under the rail feet. The situation was not cured but it was improved a lot.