Bubblings Zincs!!

[kelpline]

After our first trip up Toba Inlet in early May, I pulled the boat and polished the hull. And changed the zincs, rudder, propellor nut and trim tabs. When it came to the trim tabs, I looked at the box of used 3" cicular zincs accumulting over the years in the garage and a streak of cheap came over me. I grabbed the least used zincs and made new pairs. After all, a new set cost a whole $30 up here in Canada, despite Canada producing most of the world's zinc. About a month later I noticed that the trim tab zincs were all white and mushy, with bubbles arising! Of course I couldn't sleep at night, imaging what might be happening to the propellor. So 6 am I have the truck and trailer down to the boat launch, haul out the boat and with relief see that the prop nut is active but fine; but the trim tab zincs have been super active and shot. It must have been that the the garage pairs were made up of 2 different company's zincs, with slightly different formulas. A brand new $30 pair was installed on each trim tab. No more bubbling zincs; and I'm tossing out the box of old zincs.

 

[watson1987]

Is it possible that you used aluminum anodes instead of zinc?

When I had my boat hauled out and all zincs changed at the start of this year while getting bottom paint they used aluminum on my trim tabs by accident. My diver happened to swim by my boat a few weeks later when on another job and noticed overactive bubbling anodes too, which he eventually realized were incorrect aluminum ones.

Needless to say, I got the yard to pay for my diver to dive again and replace them with zinc ones.

 

[Rode Trip]

There's no scenario where aluminum anodes should be a problem. I'm switching my boat to all aluminum (except for the engine/gen anodes which I can't seem to find in aluminum). Aluminum anodes are good in all water: salt, brackish or fresh. Zinc is good only in saltwater. Magnesium is good only in freshwater. Aluminum anodes can still galvanically protect aluminum, and unlike zinc anodes the aluminum ones don't have the heavy metal cadmium in them which enters the water when the zinc wastes away.
I've never spent time in the NW, but here in Florida we are constantly going between salt and brackish water, with a big body of fresh if we want to cross through the state or go down the St. Johns river. Aluminum is the only practical choice but most boaters haven't caught on yet and are still using zinc because they're slightly cheaper and more common. I've seen zinc anodes turn to mush in a surprisingly short time when a normally salty/brackish area turned brackish/fresh because of heavy rains and fresh water inundating the area. I normally encourage using aluminum unless your boat is always in saltwater only or always in freshwater only.