Zinc - when it's gone how long before damage occurrs?

[Billfletcher]

I was under the boat last week, and noticed the main transom zinc was almost gone. I told my diver who cleans my boat. Well, i went under today, and its gone - completely. How long should i wait, with no zinc? If it's another week, is therefore potential for galvanic action to start pitting my underwater metals? I am not happy with him, but wondering if if you have some time before any appreciable corrosion may occurr?

 

[osd9]

The HUll zinc is protecting all the metals in the ER....including the motors, trannies, strainers, etc, etc. Replace the zinc ASAP!!!!!

 

[Lazy Daze]

Corrosion will start to get a hold on things as the anodes approach 2/3 gone (1/3 left). That's why the general rule of thumb is to replace them between 1/2 and 2/3 gone.

"how much corrosion has started" is the $64,000 question. There's no way to say how much has started or not started - there's just too many variables. Dom's last sentence sums it up.

 

[Billfletcher]

Good point about the protection of the ER as well. Well, the story gets better. The owner of the dive company also does alot of maint on my boat. I have given him alot of money over the past year (about $12K) for past neglect by the PO. I am very disappointed that this is how he returns the favor. I had a testy exchange with him a few minutes ago, and he said the zinc would be replaced tommorrow - and no apologies on his part. As I previously noted, I told him a week ago it was almost gone, and the fact that i have to follow up with him is very frustrating. In my business, i'd be fired for similar behaviour. Well, after the zinc is replaced, he is gone.

 

[kaz911]

Keep an eye on all Anodes - if they go fast (< 6 months) there might be a current leak into the water where you are. That can be a "killer" if someone jumps in the water.

And when you replace Anodes - replace all at the same time. Keep a log of when you change them. Then you will get a feel for how long they will last.

Once you know the "anode consumption" you can relax a little bit. But not a lot.

And make certain your galvanic isolator is working and has not been modified. Detach your shore power cable from Dock power - and measure resistance (Ohm) with a multimeter - between the shoreline ground plug (your power cable on the dock) and your A/C ground distribution bar on the boat. There should be NO connection between the two. If Ohm meter shows 0.1-50 Ohm - there is a connection. (And don't run your genset while doing it)

 

[fwebster]

As a rule of thumb, you should replace zincs when they are 1/2 consumed, no more. If you have the diver regularly service your boat, they why are you having to tell him about the zinc? Divers around here report the bottom condition and state of zinc erosion after every dive.

 

[Billfletcher]

Thanks for the input, all good points. I will save this, and check these items in the future. "Why do I have to tell the dive service when the zincs are gone" - That is why he is being fired. I am on my boat weekly, and know quite a few people in the marina - what goes around, comes around.