H-31 underwater bonding system

[RJ9757]

Hello all.

I've recently encountered an electrolysis issue, i.e. my shaft zinc (which has previously always lasted a year or so) apparently disappeared in a just a few weeks. There are no obvious changes to account for this problem. I suppose could be current from one of my neighbors in the marina. Or possibly my diver forgot to take his medication.

I'd like to start using a zinc 'fish' over the side to control this problem until I get it solved. What is the easiest way to connect the zinc to the bonding system?

Also, what would happen if a boat was 'over-zinked,' if that's possible?
Eventually I'll have the current measured, and figure it out, but in the meantime I was wondering if there was any downside to putting a zinc fish over the side.

Thanks in advance-
Rick

 

[Don S/V ILLusion]

It depends on 1. how your bonding system is configured, 2. whether is has any connections with sufficient resistance to mask any benefit an additional zinc could provide and 3. how far away the zinc would be from the underwater metals you want to protect.

First, if you don't have direct connections to your prop/shaft, connecting something elsewhere would be useless.
Second, the more connections, the more chance for loss due to resistance; even a slight amount will negate any benefit.
And lastly, the effective radius in salt water is between 4 and 7 feet. Putting a zinc outside that distance serves only to make you feel better.

There are other considerations not mentioned above, all of which you can eliminate by finding the cause.Even a bad bilge pump connection can suddenly arise. A bad dock power connection if you don't have a galvanic isolator can cause what you describe as can a nearby boat although he would presumably know it before you do.

It is possible to over -zinc. The more zinc you add where there is a current path, the bigger the battery becomes you just made.

Time to get the sliver chloride anode out and find the source.