Yanmar Saildrive Burning Zincs!

[AlexCollier]

My Beneteau Oceanis was burning through a couple of zincs a season - even after I fitted galvanic isolators...
There is only room for a small conical zinc on the end of the Maxprop.

So I installed a "Guppy" anode that is connected directly to the ground bolt on the diesel engine.

The guppy is put over the side when ever the boat is not moving.
It is positioned at the nearest point to the prop and at the same depth.
The zincs last a season now...

[fstbttms]

Originally Posted by RiffRaffSoCal

I’ve changed divers... just in case.

You suspected that your rapid anode depletion was somehow the diver's fault? Seriously? OMG.

[RiffRaffSoCal]

No I’m not that much of a jerk…the dive co I had was flaky, often charged me different prices for anodes (plus or minus 60%) told me I had massive bubbling on my new bottom paint, etc. Hired a different diver, for lots of reasons, but he confirmed rapid anode depletion

[jmschmidt]

I'm not surprised. They combine the worst characteristics of inboards and outboards. Sail drives should be outlawed except for racing boats that can be taken out of the water after each use. Zincs are a minor issue, wait until you hit something in the dark of night in unfamiliar waters and the drive is ripped out of the bottom and your boat sinks. At the very least these contraptions should live in their own water-tight compartment. If not you should build your own version of a stern collision bulkhead between the engine and the rest of the boat.

[sinnerman]

Originally Posted by sailingchiro

I was burning through zincs several years ago. (3 months)
For me, I had to find where green and white were hooked together. Green and white should only be hooked together when not on shore power but using house AC, such as inverter and genset. When on shore power, green and white are disconnected.

I took all my greens off the AC panel and did resistance check between green and white. I found 3 sets that were hooked together. Went to the source of the problem and repaired (in my case it was the inverter charger). No more zinc problems. I did recently have a problem and found it to be a Xantrex battery charger. I don't know why yet. I stopped using the charger.
I do know my starboard zinc is eating faster than my port hull but recently have a new neighbor with suspected wiring issues. But my zincs still last about 9 months to a year.

This is a good point. Even though your AC boat wiring may be correct, there may be AC appliances plugged in shorting the white AC neutral to the green AC ground. Disconnect the shore power cable from the boat and measure in megaohms between the white neutral and green ground wires. (can be done at the connector, or in the panel.) Reading should be many megaohms (ideally infinity/"open circuit").

Electrical currents in water seek the easiest path which may be include entering your sail drive, following a conductive path inside the boat and then exiting another under water fitting on its way "home".

[Library70]

I replaced a starter and 2 months later my SD50 zink was badly corroded- it previously lasted 2 years. I tested for voltage between the negative battery terminal and the engine block and found 0.046 volts. Removed the positive terminal from the starter and found 0.000 volts. I haven't checked the replacement zink yet (3 months) but I'm guessing it will be ok.

[RiffRaffSoCal]

Does it matter they only thing running or connected when connected to dock shore power is my 12v factory installed fridge and the battery charger…

[gulfcoastsailor]

Originally Posted by RiffRaffSoCal

I’m so perplexed!

Don’t be. Be the dock detective. It’s a neighbor.

[RiffRaffSoCal]

But wouldn’t others have this issue? The nearest 6 boats have indicated no issue with zincs and again I have an isolator installed…

[fstbttms]

Originally Posted by gulfcoastsailor

Don’t be. Be the dock detective. It’s a neighbor.

It's almost never the neighbor.

[Searles]

Have you got a bronze prop ,even with a coating if not fitted with an isolating bushing may be a start point ,I take it you are new to this vessel .⚓️⛵️

[RiffRaffSoCal]

I bought it a year ago…new but not to sailing and boat ownership. This is my first saildrive however.

I’ll double check the prop and consider swapping it out (good to have a spare anyway).

[David B]

Originally Posted by RiffRaffSoCal

Hi! And thanks in advance for anything help.

We have a 2015 Hunter with an SD 25 Yanmar sail drive. We are burning through Zincs in 6 weeks. Had a well respected marine electrician out and he said the system is well/properly grounded but that in his estimation the two ring zinc system is not enough to protect the sail drive.

Thanks!

Sorry, but well-respected or not, that comment regarding the anode (zinc) system would worry me. The protective anode on a saildrive works very well (ours typically lasts a year or two, depending on where we are), and the manufacturer has been doing it this way a while now .....

In regard to your comment on internal pencil anodes - if you have any in there at all, they have absolutely no effect on what is happening to the saildrive leg.

What should have happened when your marine electrician came on board, was measurements for stray currents.

You mentioned that you have a galvanic isolator on board, but I would want to be sure it really was connected correctly - and also that it is fully functional.

Has this erosion of your anodes been an issue since you have owned the boat?
Has it just recently become an issue?
Have you recently moved berths?
Have you changed your power configuration from the shore?
Has a new boat recently moved in to a berth near you?

These are the sort of questions that will determine the issue (assuming of course you are not putting magnesium anodes on the saildrive ....).
But first up, a check for stray currents needs to be made.

I hope that helps you determine the issue.

David

[RiffRaffSoCal]

Many thanks for the thoughtful reply.

He removed the dc and 110 panels and checked connections. He did check for stray currents and reviewed the various bonding/grounding (I forget the proper terminology here). He did notice that we weren’t getting a solid connection from our shore cable and when j observed it, it was corroded and part of the cable insulation was cut exposing some of the wire (not good!) so I quickly replaced it with a new one. To his credit, Yanmar published a service bulletin in April 2010 regarding a large number of customers experiencing corrosion and advised that additional zincs could be necessary. So I’m not the only one…but it seems it shouldn’t be necessary…

Thanks for the point about the pencil anode.

We got the boat last summer and upon haunt out they had some blistering on the keel which the surveyor thought it was due to a stray current but that it would be easy to fix. I got a concession for some bottom paint and a month later had the bottom repainted with the proper paint used on the sail drive too. The yard said the blisters were small and nothing to be concerned with - and she was splashed and put into the water in the same slip since August 2020. The whole time we’ve been burning zincs at a fast rate. The seller certainly didn’t disclose an issue prior to sale so can’t speak to any issue before.

[David B]

Good information.

So I take it that when the electrician checked for stray currents, he didn't find any?
Wondering again if something has changed - especially with another boat nearby that may not have been there at the time your electrician was there.
There has to be a significant factor that is causing this rapid erosion.

Basically, for that level of erosion, you have an electrical circuit - either from your saildrive to the anode, through the seawater (this is electrolytic errosion - the seawater is the electrolyte), to somewhere else on your boat such as a through-hull, and back via earthing to your saildrive).
Or, from your saildrive, to the anode, through the seawater to something else out there that is connected one way or the other to the shore power, and back to your boat via your shore cable.

To prove this, get a pair of identical anodes - you can buy ones that are moulded like a fish, and are intended to be hung over the side for additional protection.

Connect a wire to one (see below as to where the other end of the wire goes), and hang it over the side for a week.
Take that off, and connect the other one to the wire, but before you hang it over the side for another week, disconnect your shore power.
At the end of the two-week period, observe the difference between those two fish anodes. That should show one way or the other whether it is your boat, or something 'out there'.

And on that, if you have one, you could put a test meter in line to see if there is any current flowing in that wire - with or without the shore power connected.

And the wire? That needs to be connected to your boat earthing system (assuming your saildrive is also part of the earthing system - otherwise, direct to your saildrive). Make sure that is the case before you hang those anodes.

I hope that will help you.

David