See a Grown Man Cry - Corroded Prop !

[s/v Jedi]

Originally Posted by Dockhead

So what I'll try to do is try to engineer an A/C system which will not overwhelm a 16 amp shore connection. That will be a better A/C in any case -- lighter, cheaper, taking up less space, besides being usable with any shore power connection (how stupid would that be, having an air conditioning system which you often can't use because there's not enough power for it). I notice that the 16,000 BTU Cruisair unit uses less power than the 12,000 BTU unit, and in fact only needs 5 amps full load, cooling. So at worst two of those should be plenty, and I will have 5 amps or so left over for other loads. At best maybe one 16,000 BTU unit plus a 7,000 BTU unit for the aft master cabin, which needs only 3 amps, which would leave 7 amps for other loads out of a 16 amp shore connection.

You are looking at the StowAway Turbo systems; for your main unit I would recommend this one instead: products - Dometic

You can choose between 18kBTU or 24kBTU. I have the smaller one. It uses just 5.4A @230V/50Hz which is very efficient plus it has a cupronickel condenser. But remember that the consumption of a pump must be added to that. I use a March pump and wouldn't know something better than that.
I re-used the simplest digital control that I already had from the old unit (SMX-II control).

The jet of cold air from these units is unbelievable. You actually have to hold on to something or it will blow you away ;-))

cheers,
Nick.

[DotDun]

Originally Posted by chala

So yours installation can leak up to 30mA continuously.

No leak, the GI diodes stop that. The 30ma means I won't die when the 1.2v GI diodes allow current to flow on the ground path. The 30ma is the fault isolation main breaker in the AC panel.

[SabreKai]

The 120v system on Sabre Dance consists of the shore power cable into its socket. From the socket it leads to a duplex recepticle. Period.

I am going to rebuild the entire thing, and based on this tread, an isolation transformer is included in the new system.

Sabre

[bill good]

Just skimmed thru but would also add I have seen this where there has been an insulated coupling has been installed in the prop shaft adding to the electrolysis sum. I like all metal parts bonded as it is too easy to make potential differences (batteries) with different metals in salt water. If that could be your trouble check with a voltmeter across the coupling for DC volts. If you can see volts then put a bond strap.

[Boracay]

I had a brain snap when I saw a post about correct wiring for an automatic bilge pump.

So I dropped the red probe on my multimeter into the bilge water - result +0.04V. Switched bilge pump off - result 0.00V.

So my old bilge pump/switch combo has been churning electrons round my boat.

Short fix - lift the bilge pump up 4" so it doesn't sit in the bilge water. I'll use the manual pump to keep it under control.

Long fix - find how to wire a bilge pump properly, get a better pump switch, keep it higher in the boat, use a manually switched pump to empty the bilge?

[Stillraining]

Originally Posted by Boracay

I had a brain snap when I saw a post about correct wiring for an automatic bilge pump.

So I dropped the red probe on my multimeter into the bilge water - result +0.04V. Switched bilge pump off - result 0.00V.

So my old bilge pump/switch combo has been churning electrons round my boat.

Short fix - lift the bilge pump up 4" so it doesn't sit in the bilge water. I'll use the manual pump to keep it under control.

Long fix - find how to wire a bilge pump properly, get a better pump switch, keep it higher in the boat, use a manually switched pump to empty the bilge?

This is a test I need to do as well......one question though....mine sits in a separate 10" x 18" by 6" deep well with no keel bolts or anything else but solid fiber glass...so what would any stray current hurt?

[Dockhead]

Originally Posted by Boracay

I had a brain snap when I saw a post about correct wiring for an automatic bilge pump.

So I dropped the red probe on my multimeter into the bilge water - result +0.04V. Switched bilge pump off - result 0.00V.

So my old bilge pump/switch combo has been churning electrons round my boat.

Short fix - lift the bilge pump up 4" so it doesn't sit in the bilge water. I'll use the manual pump to keep it under control.

Long fix - find how to wire a bilge pump properly, get a better pump switch, keep it higher in the boat, use a manually switched pump to empty the bilge?

I'll do the same. You were measuring potential between what -- bilge water and your grounding/bonding system? How would that work? Where was the black probe?

[Boracay]

Being a steel boat I just put the black probe on random bits of steel. Engine, engine mounts, hull.

It came as a bit of a surprise as I did put a fair bit of epoxy resin into the bilge and I thought I had a fairly thick coating.

The real test would be to put the black probe (maybe with an extension) on the propeller shaft, and to turn the bilge pump on and off.

As it went on and off with the switch that's electrolysis, not galvanic corrosion.

[Dockhead]

Originally Posted by Boracay

Being a steel boat I just put the black probe on random bits of steel. Engine, engine mounts, hull.

It came as a bit of a surprise as I did put a fair bit of epoxy resin into the bilge and I thought I had a fairly thick coating.

The real test would be to put the black probe (maybe with an extension) on the propeller shaft, and to turn the bilge pump on and off.

As it went on and off with the switch that's electrolysis, not galvanic corrosion.

But you need something to measure potential against. If the black probe is connected to your bonding system (or your shaft, etc.), wouldn't the potential be zero? Even if it's eating your boat up?

[Stillraining]

Im confused.

[Dockhead]

Originally Posted by Stillraining

Im confused.

OK, look. The voltmeter reads electrical potential, right? Between two conductors?

So if you stick the red probe in the bilge water, then the black probe has to be stuck somewhere else, right?

So where would you expect the current to be flowing to, if you've got a problem?

To the shore power ground, maybe?

To your bonding system?

To the ocean?

To the negative side of your DC power system?

That's the question. I don't have too good expertise in electrickery, so apologize if it is a stupid question.

[Boracay]

I really have no idea how it works, or doesn't.

I found a voltage difference switchable by the bilge pump switch, hopefully I've removed it, and I'll continue to upgrade my system to totally eliminate it as the opportunity occurs (things break!).

Possibly you're looking at it the wrong way, assuming that boats are either insulators or conductors. From my very limited experience of one steel boat it seems to work more as a bunch of resistors of varying values. I would suspect that fibreglass, particularly older fibreglass, may be similar.

From a practical point of view I want to prevent electrical corrosion of my propeller, my hull, other below the waterline components and non essential loss of my anodes. I don't care how it happens. I just want it to happen.

[GordMay]

Originally Posted by Dockhead

OK, look. The voltmeter reads electrical potential, right? Between two conductors?
So if you stick the red probe in the bilge water, then the black probe has to be stuck somewhere else, right? ...

See ➫ http://www.cruisersforum.com/forums/...sion-2469.html

And ➫ http://www.fluke.com/Application_Not...r/B0269b_u.pdf

"... Sign of corrosion potential assumes that the "COMMON" or negative (Black) terminal of the voltmeter is connected to the reference electrode and the "VOLTS-OHMS", or positive (Red) terminal is connected to the metal to be measured. The reference electrode must be immersed in the same body of electrolyte as the metal being measured, preferably in close proximity ..."

[Dockhead]

Originally Posted by GordMay

See ➫ http://www.cruisersforum.com/forums/...sion-2469.html

And ➫ http://www.fluke.com/Application_Not...r/B0269b_u.pdf

"... Sign of corrosion potential assumes that the "COMMON" or negative (Black) terminal of the voltmeter is connected to the reference electrode and the "VOLTS-OHMS", or positive (Red) terminal is connected to the metal to be measured. The reference electrode must be immersed in the same body of electrolyte as the metal being measured, preferably in close proximity ..."

Now we're getting somewhere. Thanks for the info and leads. So that would be equally valid for a potential galvanic corrosion problem, as for an electrolytic corrosion problem like current leakage from a bilge pump?