Zinc wastage and voltage at fittings

[smokey73]

1994 Hunter 40.5

I know there was an earlier discussion about zincs lasting only 3 months or so but I didn't want to drag that one out. I seem to have the same problem and took some potential measurements but don't know what to make of them. Hoping Maine Sail or someone else with experience in the area can give me some pointers.

Location Measured Voltage
Engine 0.12V
Shaft . 0.12V
Strut bolts 0.16V
Elect Panel Ground 0.15V
Battery Ground 0.12
Keel bolts 0.39V
Mast ground 0.38V

Diesel Eng thru hull 0.82V
A/C Thru hull 0.91V
Aft Head thru hulls 0.86V - 0.91V
Fwd Head thru hulls 0.86

From the above it is clear (I think) that the thru hulls are not bonded to the grounding system. There is no appreciable difference between readings with battery on or off, equipment breakers closed or open, or Shore Power connected or disconnected. The numbers vary in the second significant digit or less

For the moment I have put a "zinc fish" overboard, attached to the engine ground. Don't know if this will help or possibly even make me "over zinced" but its just for the moment until I can figure out why my zincs may be wearing out quickly.

Any pointers or suggestions about where to look or what I may be doing wrong in my measurements? What values should I be seeing. I know that with dissimilar metals there will be some voltage and the zincs are designed to sacrificial but I'm surprised I am having to replace them at the 3 1/2 month mark. I have 2 shaft zincs and a cone zinc on my Maxprop. There are no zincs on the hull or on the keel.

 

[Anonymous 121765]

Smokey,

I assume you are in a marina. I assume nearby boats are on shore power with some or more running systems (live-a-boards ?).

This would be eating your zincs quicker especially if you're in a closed or dead end body of water. The electrical experts should give you additional info pal in this thread.

 

[alexco38]

Isolation transformer

Newer hunters has optional isolation transformer in the shorepower circuit.

You could also google Galvanic Isolator.
New Hanse boat comes with it.

Yes you have a shorepower ground loop. You have to find it.
Some where you shorepower ground has wired to the boat DC ground.

My zinc last 4 years. Plug in shorepower all season.

 

[fstbttms]

My zinc last 4 years.

Maybe that's because you're in freshwater and zinc anodes are ineffective in freshwater.

 

[Charles Erwin]

First - "over-zincing" is not a concern with a fiberglass boat. The zinc fish will certainly extend the life of the zinc presently on your boat and will do no harm whatsoever. It works just fine the way you are using it provided there is nothing that electrically isolates the shaft from the "motor ground."

Next (assuming you are measuring with a zinc reference and also the fish was not in play) your values show you are well and properly "zinced" at the present time. Your values show the through hulls and the keel bolts are not bonded to the rest of the underwater metals - which is just fine. Also looks like the strut is bonded - probably to the motor block - but that connection is probably in need of cleaning.

Questions:

What is your rudder shaft value. When did you last install your zincs. Where are your zincs mounted. How many are mounted. You said you get no value changes shore power physically connected/disconnected. Did you measure with your battery charger on and off. Do you have a galvanic isolator. Do your neighbor's complain of accelerated zinc loss. Has a neighbor recently left or arrived.

So far - your data suggests that your zincs are fresh, the marina and neighbor boats are not presently players. The present zinc is protecting the shaft, prop, strut, and possibly also the metals in the rudder. Your high rate of zinc loss may be because the quantity (actually overall surface area) of zinc mounted on the boat needs to be increased.

Consider continued use of the zinc fish, keep track to see whether this additional zinc extends the life of the permanent mounted zinc, and also how much longer it takes to erode your boat mounted zinc.

Charles