Zinc Anodes

[mitch184]

So I was wondering if anyone had any experience with weld on vs. bolt on zincs on aluminum boats? I currently have one zinc welded on and then the normal zincs on the motors. I like the idea of the weld on zincs but I'm not sure what exactly the options are when the weld on zinc corrodes? I know I'd have to get it cut off and rewelded, but I was thinking of adding more zincs now to try and slow the corrosion down. Although after about 6 months the weldon zinc doesn't seem to have changed too much. Darkened up maybe a little. That and since there is no paint/vinyl/sealer on the sides or bottom now the extra protection for another zinc or 2 seemed like a good idea.

Wanted to see what you boat gurus thought about it.

[Nelly]

Hey 184!
How ya doin? Rate of zinc sacrificial anode erosion is a function of hull soak time, square footage of hull area and proximity to electrical influences both on board and in a marina.
For example, mooring your boat in a marina equipped with shore power is very handy but if a boat close to you is using an automotive type charger on his batteries, you will experience increased erosion on your zincs. Automotive (or non marine) chargers electrify the negative side of the charger so 120v power gets dumped right in the marina!

Welded on zincs work just fine and are very durable as the molten zinc is poured in a mold around the aluminum strap which is then welded to your hull. You're correct in that the only way to service them is to take the ol' grinder to the welds and then weld on new zincs.

If I were you, I would also add a bolt on zinc to your hull and see how active it is. If it turns roughly the same color as your welded zinc, you're in business. If it has a much quicker rate of erosion you've got an issue so let us know. Since in this case, your asking your zinc to protect the entire bottom of your boat adding a couple of bolt on zincs is wise.

You also mentioned that your boat does not have bottom paint. Keep in mind that bottom paint retards the rate of marine growth such as moss and barnacles. Zincs have little to do with preventing organisms from attaching themselves to your boat. That being said, I've never seen a barnacle on a zinc!

Remember, for a trailer boat, zincs last a good while, but if you keep the boat in the water for any period of time you've really got to watch them!
Great question! Thanks for asking it here!

[mitch184]

Doin good Tom, just running thru the boat here before it sees some solid saltwater time. I was hoping you'd chime in since I remember you being a big zinc guy. I was thinking of adding one or two to the transom and then one on the inside of the hull near the transom. Here's one for you, have you ever hear of anyone putting a smaller zinc on the bottom of the hull near the bow? maybe one near a lifting strake?

[Nelly]

You mean I'm a big guy that's into zinc or a guy that's into big zincs???

Either way you're right!

To your question about zincs forward on a hull? Yes, it's commonplace on commercial vessels and good practice if your boat allows a solid mounting location without drilling through the hull.

Zincs that are mounted forward will experience increased erosion due to the volume of water that will flow across their face as your boat reaches planing speed. A good indicator of a zinc's effectiveness is the rate at which it dissolves. Don't mistake hydraulic erosion with galvanic corrosion. You'll be able to tell the difference as the zinc that is doing it's electrical job will show pitting and the water-scrubbed anode will remain smooth.

Hope that helps!