Schrödinger's cathode

[nigelmercier]

Since having had to replace the lower leg on my saildrive due to corrosion, I've become paranoid about it. The problem started (I think) when a new antenna was fitted to the mast, which earthed the mast and thence the keel. This was coupled with an poorly insulated connection on my starter motor which earthed the normally isolated casing, and thence the engine and saildrive. So now there was a circuit for the anode to generate a voltage, and it fizzed into oblivion.

I've been trying to think of a way to monitor is such a current exists, but of course in doing so I would cause it to occur.

Not really looking for a solution here, I just had to use the thread title when I thought of it

[Edit for more info]
My combination of Volvo Penta MD22P and 120S saildrive are not meant to be isolated from each-other. See original thread here: http://www.ybw.com/forums/showthread.php?347803-Saildrive-corrosion-galvanic-isolation-and-grounding and conclusion here: http://www.ybw.com/forums/showthrea...isolation-and-grounding&p=4024608#post4024608

 

[vyv_cox]

PM sent

 

[prv]

What kind of engine?

My saildrive is insulated from the engine block by plastic gaskets, and plastic sleeves and washers on the bolts. The manual is most insistent that this insulation be maintained, and describes how to test it to make sure. I believe this is the case for all Volvo saildrives, but I don't know about Yanmar or others.

Seems like it would be a solution to your problem though.

Pete

 

[AngusMcDoon]

PM sent

Can't we all have a read?

 

[macd]

I've been trying to think of a way to monitor is such a current exists, but of course in doing so I would cause it to occur.

Not really looking for a solution here, I just had to use the thread title when I thought of it

What you need is a Heisenberg by-pass diode connected to a voltmeter. Maplins have 'em quite cheap. Of course, if you actually look at it, it won't work.

 

[vyv_cox]

Can't we all have a read?

Yes, when/if the answer comes back from the expert I have consulted.

 

[nigelmercier]

What kind of engine? My saildrive is insulated from the engine block by plastic gaskets, and plastic sleeves and washers on the bolts.

I forgot to mention that my engine and saildrive combination are not meant to be insulated from each-other, I have edited my OP with the details.

 

[VicS]

Since having had to replace the lower leg on my saildrive due to corrosion, I've become paranoid about it. The problem started (I think) when a new antenna was fitted to the mast, which earthed the mast and thence the keel. This was coupled with an poorly insulated connection on my starter motor which earthed the normally isolated casing, and thence the engine and saildrive. So now there was a circuit for the anode to generate a voltage, and it fizzed into oblivion.

I've been trying to think of a way to monitor is such a current exists, but of course in doing so I would cause it to occur.

Not really looking for a solution here, I just had to use the thread title when I thought of it

You pretty well figured out the causes of the problem IIRC and you established that your engine and saildrive were not, and could not be, isolated from each other

I think the way to monitor things is with a silver /silver chloride reference electrode.

I suggest you take a look at the "Galvatest" system which forumite "coreng" attempted to sell to us all a while back. http://www.galvatest.com/

It will be a bit of a chore I guess to regularly monitor it but not so much of pain in the wallet as another saildrive leg failure

 

[Blueboatman]

Would an inexpensive underwater usb video camera on a stick do the trick?

V v clever title btw

 

[nigelmercier]

I think the way to monitor things is with a silver /silver chloride reference electrode...

I could connect a meter between my engine/saildrive and battery negative/ground. A voltage of 0.47V here probably means they are not connected, so all is well. Perhaps I could make a voltage comparator circuit (with a push button and LEDs) to check this. I need to do some more tests, first of all I need a lump of cast iron to repeat the measurements in "laboratory conditions" (my shed).

V v clever title btw

Thank you. I thought of it, and just had to start the thread

I now have two anodes hanging off the transom (told you I was paranoid), both connected to the engine/saildrive. I check these before and after every trip to the boat, so I'm not sure a camera would help.

 

[CreakyDecks]

I could connect a meter between my engine/saildrive and battery negative/ground. A voltage of 0.47V here probably means they are not connected, so all is well. Perhaps I could make a voltage comparator circuit (with a push button and LEDs) to check this. I need to do some more tests, first of all I need a lump of cast iron to repeat the measurements in "laboratory conditions" (my shed).


Thank you. I thought of it, and just had to start the thread

I now have two anodes hanging off the transom (told you I was paranoid), both connected to the engine/saildrive. I check these before and after every trip to the boat, so I'm not sure a camera would help.

You said originally that you put it down to a new antenna installation. Have you made measurements with the antenna connected and disconnected at the radio?

 

[nigelmercier]

You said originally that you put it down to a new antenna installation. Have you made measurements with the antenna connected and disconnected at the radio?

No, because I decided that having the keel grounded was probably a good thing, and intend to add a strap for this purpose. I had plans for this some time before the problem arose, but if I had done it then the corrosion would have been my fault (at a time when I shared the boat).

 

[CreakyDecks]

The reason I asked is because I understand that there are devices that will still protect against lightning strikes but block DC, so if that is how the connection is being made it might be a way to break it.