Losing zinc rapidly

[Knotical]

Hi, we launched a month ago and I had to get the boat out for a short haul today (long story) - anyway, I noticed that my month old zinc is almost gone (see photo, this was new when we launched in June). Now, we are at least 400 yards away from the closest marina and because of a relatively slow summer even our moorings are spaced far apart, I doubt someone else’s stray current is eating up my anode. That brings me to the possibility of leakage in our 12v system. Can you please give me advice on how to find the leak and how to fix it? I shut off the battery switch when I leave the boat, bilge is obviously on (has a float switch, does not have a manual switch).

Thank you.

Darshan

[grantmc]

Here's a link to the downloadable pdf of the 12 Volt Doctors Practical Handbook by Edgar Beyn. Excellent section about chasing down a stray current.

[Knotical]

Originally Posted by grantmc

Here's a link to the downloadable pdf of the 12 Volt Doctors Practical Handbook by Edgar Beyn. Excellent section about chasing down a stray current.

Thank you very much, will start reading tonight.

[slug]

Originally Posted by Knotical

Thank you very much, will start reading tonight.

Hard to say

It’s possible you don’t have enough anode mass in relation to exposed underwater metal

The bare stainless prop shaft doesn’t treat your anode with respect

If you use antifoul with a high copper oxide content you overload anodes

Remember , if your boat had no underwater metal , you would require no anodes

[Knotical]

Originally Posted by slug

Hard to say

It’s possible you don’t have enough anode mass in relation to exposed underwater metal

The bare stainless prop shaft doesn’t treat your anode with respect

If you use antifoul with a high copper oxide content you overload anodes

Remember , if your boat had no underwater metal , you would require no anodes

I hear you, but even if there’s a huge amount of metal underwater this degree of disintegration is hard to imagine without a current accelerating it. The yard painted the bottom before launch last month, I don’t know which paint they used - should I ask them? Also, does the keel (lead) play any role in this?

[gamayun]

I'll give you my experience but it may be just anecdotal because I did a lot of work on all the systems over the first years. Initially, I was going through zincs every 3 months. The bottom paint had probably accumulated over the life of the boat's 30 years. It was chalky and flakey and even had a layer that looked like they never cleaned off the dried algae. I could not sand it back to any good point. The paint on the keel I could peel back in whole layers. In talking with a friend who was helping me, contact between the seawater and keel creates an electrical connection. We wrapped the keel-to-hull joint in fiberglass and faired then primed everything and painted. However, shortly after, the old wiring was also ripped out and upgraded so that might have also contributed. I recall that each step helped incrementally. I now go a long time between zinc changes. I'd need the check my records on this, but I think it's now at least 8 months maybe longer. I dive more frequently than that so just change them (one on prop shaft, one on Max Prop hub) when they look like they need refreshing. The boat is also in a marina in close proximity to other boats.

[a64pilot]

If the battery switch is left off, and the anode continues to be eaten away, that pretty much leaves the circuits that are still energized.
I believe a bilge pump is a common cause.

[YANDINA]

To check if the problem is an on-board 12 volt leak, detach the positive cable(s) from your battery(ies) and connect (one at a time) back to the positive terminal through a DC ammeter. This will indicate how much residual 12 volt leakage you have and theoretically it should be zero. If greater than 0.1 amps, disconnect connections from the positive circuit one at a time until you see which one is drawing the current.

To protect your meter from in-rush damage, set the meter on the highest amp range and connect it between the cable and battery terminal before removing the cable. Then remove the cable from the battery and select more sensitive meter settings to get a reading. That way any in-rush loads that could damage the meter are already charged.

[Knotical]

Originally Posted by YANDINA

To check if the problem is an on-board 12 volt leak, detach the positive cable(s) from your battery(ies) and connect (one at a time) back to the positive terminal through a DC ammeter. This will indicate how much residual 12 volt leakage you have and theoretically it should be zero. If greater than 0.1 amps, disconnect connections from the positive circuit one at a time until you see which one is drawing the current.

To protect your meter from in-rush damage, set the meter on the highest amp range and connect it between the cable and battery terminal before removing the cable. Then remove the cable from the battery and select more sensitive meter settings to get a reading. That way any in-rush loads that could damage the meter are already charged.

I will try this, thank you.

[Knotical]

Originally Posted by a64pilot

If the battery switch is left off, and the anode continues to be eaten away, that pretty much leaves the circuits that are still energized.
I believe a bilge pump is a common cause.

I don't have a manual switch for the bilge pump, does that change how I check for leakage?

[Knotical]

Originally Posted by gamayun

I'll give you my experience but it may be just anecdotal because I did a lot of work on all the systems over the first years. Initially, I was going through zincs every 3 months. The bottom paint had probably accumulated over the life of the boat's 30 years. It was chalky and flakey and even had a layer that looked like they never cleaned off the dried algae. I could not sand it back to any good point. The paint on the keel I could peel back in whole layers. In talking with a friend who was helping me, contact between the seawater and keel creates an electrical connection. We wrapped the keel-to-hull joint in fiberglass and faired then primed everything and painted. However, shortly after, the old wiring was also ripped out and upgraded so that might have also contributed. I recall that each step helped incrementally. I now go a long time between zinc changes. I'd need the check my records on this, but I think it's now at least 8 months maybe longer. I dive more frequently than that so just change them (one on prop shaft, one on Max Prop hub) when they look like they need refreshing. The boat is also in a marina in close proximity to other boats.

Scary to think the keel lead could be eating away the zinc. The way it's going I will have to replace zinc 3-4 times/season - hardly practical. I only have a very small amount of shaft visible inside the boat, could I add small piece of zinc there and replace as necessary or it has to be in contact with salt water?

[a64pilot]

Originally Posted by Knotical

I don't have a manual switch for the bilge pump, does that change how I check for leakage?

Disconnecting everything via the battery switch ought to isolate everything that is powered thru the switch.
From there I would disconnect the pos terminal to the bank and check for current, if it exists, then start disconnecting things that are still connected, one at a time, when the current drops to zero, you have most likely found your culprit.
Many times there are hidden or “sneak” circuits, for example my Icom 802 has a crystal heater to keep frequencies stable, and most stereo’s now have a keep alive power wire for programming and the clock etc.

Depending on how complex your system is, and how many times it’s been modified, you may be in for a real search.

Many times there are systems that are left powered that connect directly to the battery switch on the battery side, bilge pumps and maybe propane sniffers etc.

[CharlieJ]

@Knotical

Scary to think the keel lead could be eating away the zinc. The way it's going I will have to replace zinc 3-4 times/season - hardly practical. I only have a very small amount of shaft visible inside the boat, could I add small piece of zinc there and replace as necessary or it has to be in contact with salt water?

Don't look at this process as "the keel could be eating away the zinc." If the keel is unpainted and if the lead is in contact with the water and if the keel is bonded to the B- system, then the zinc (the anode) "sees" the lead keel as a cathode and will provide the cathodic protection current to protect it. So the question is, is the keel painted?

Why did the yard not paint the propulsion shaft? Is the prop painted? If they were painted, that would reduce the cathodic protection load on the anode.

[Knotical]

Originally Posted by CharlieJ

@Knotical

Don't look at this process as "the keel could be eating away the zinc." If the keel is unpainted and if the lead is in contact with the water and if the keel is bonded to the B- system, then the zinc (the anode) "sees" the lead keel as a cathode and will provide the cathodic protection current to protect it. So the question is, is the keel painted?

Why did the yard not paint the propulsion shaft? Is the prop painted? If they were painted, that would reduce the cathodic protection load on the anode.

The keel is painted but not faired or primed and there is lead showing at a few spots. I learned all about bottom job just this spring and didn't want to shorten my sailing season so left it as is with plans to fix it next winter.

Wrt painting shaft and prop, I asked several boaters and even the machine shop which did the work - they all said to leave it alone. I know there are different schools of thought on this, your opinion is welcome too.

[Knotical]

Originally Posted by a64pilot

Disconnecting everything via the battery switch ought to isolate everything that is powered thru the switch.
From there I would disconnect the pos terminal to the bank and check for current, if it exists, then start disconnecting things that are still connected, one at a time, when the current drops to zero, you have most likely found your culprit.
Many times there are hidden or “sneak” circuits, for example my Icom 802 has a crystal heater to keep frequencies stable, and most stereo’s now have a keep alive power wire for programming and the clock etc.

Depending on how complex your system is, and how many times it’s been modified, you may be in for a real search.

Many times there are systems that are left powered that connect directly to the battery switch on the battery side, bilge pumps and maybe propane sniffers etc.

My system is not complex at all. You are suggesting the same process as Yandina above, right?