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Old 01-04-2010, 11:00   #16
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Well, I find all this advice pretty persuasive. We are away from our boat a lot so maybe I'll just unplug her, maybe even without solar. I can always plug in and charge for a few hours before setting off -- anyway it takes a few hours at the very least to get ready to go, and usually it's overnight. Now over the winter I needed the shore power because I had electric heaters going below, but that's already not a consideration (until late next fall).

As to the transformer -- well, bulk and weight are always a consideration, but I agree that on our boat it is less critical than others. Even with a 100-odd kilos of hand tools (allusion to another thread), nuts, bolts, screws, power tools, a ton of water on board and two-thirds of a ton of diesel, we ride high above our load lines. But we have 30 amps of shore power so the 3.6kVA transformer won't be enough -- we will need the 7kVA model which weighs a fairly massive 28kg. Even on our boat, it is not trivial to find a good place for something like that, and not eat up space needed for something else. But I will definitely take a hard look at it, after all this advice. Thanks.
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Old 01-04-2010, 12:11   #17
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wow you have a lot of shore power.... can't imagine what that is needed for on a 54' sailboat on the Solent ;-)

I would unplug and use some solar with MPPT controller. Batteries last longer when fully charged. As I think the big power items are washer/drier and A/C you could just plug in when you use those (charge batteries at the same time) and unplug (not just switch off) afterward. No need for the transformer.

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Old 01-04-2010, 13:23   #18
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wow you have a lot of shore power.... can't imagine what that is needed for on a 54' sailboat on the Solent ;-)

I would unplug and use some solar with MPPT controller. Batteries last longer when fully charged. As I think the big power items are washer/drier and A/C you could just plug in when you use those (charge batteries at the same time) and unplug (not just switch off) afterward. No need for the transformer.

cheers,
Nick.
Well, 30 amps @ 230v is just 6.9kVA, about the same as what the generator produces, and not quite enough to run air conditioning without load balancing, soft starts, and so forth. I don't have air conditioning but probably will some day. I do have a washer/dryer which is incredibly useful (I had no idea how much so before). The system is designed for 30 amps throughout so I don't know why I would want to create a bottleneck.

But I like the unplugging idea. I did do some more reading on the transformers -- the Victron one costs $2,000! We don't live aboard for long period at the dock, and we prefer to overnight at anchor, so a little bit of being hooked up just when we are consuming power shouldn't be too bad on the zincs.

But wouldn't a galvanic isolater be ok for this purpose? It's like 1/5 the cost, even with the malfunction alarm, and much less space-hungry. Other than the danger to life in case of open-circuit failure (which you have an alarm for), I don't see what's bad about it. Much less dangerous than propane on board, to put it in perspective, or am I missing something?
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Old 01-04-2010, 15:20   #19
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Yes, a 7kW transformer is costly. We do fine with 3.6kW on a 64' boat with A/C in the tropics but that is in addition to other measures like awnings.

The problem with a galvanic isolator isn't that it is dangerous like a propane bottle can be; the problem is that it only provides partial protection and that it fails when protection is most needed (like in very hot marina's). The alarm is only useful when you are aboard to disconnect shore power when it goes off. While the alarm is going off, there is no protection (i.e. ground circuit is active). It is a semi-conductor that is isolating ground and one property of semiconductors is that under certain circumstances they will conduct. Most modern galvanic isolators will "re-connect" ground when the potential difference is 1.4V or more. That voltage is the sum of DC + AC voltage, for example 1.0V AC plus 0.4V DC. The damage on your prop indicates a bigger fault than that so the galvanic isolator might not protect at all.

You wrote that you need to "load balance". Does that mean you have more than one phase or more than one cord?

There are more options; we have a smallish (12V 50A) charger that galvanically isolates line input from DC output and you could use something similar outside of your normal shore power system, without connecting it or bonding it to ships ground.

ciao!
Nick.
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Old 01-04-2010, 20:56   #20
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FWIW- it is unlikely that the marina is "hot"; that is another wive's tale perpetrated by "old salts" who think they know more than they actually do. What is far more likely to be the case is an electrical issue aboard your own boat or possibly a neighboring boat. Keep in mind when you are plugged in to the shore power system, you are in electrical contact with every other boat on that particular circuit. You could be sharing someone else's problem. But when rapid-onset corrosion issues crop up, look to your own boat first.
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Old 01-04-2010, 20:58   #21
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Ah, and how about hiring a diver to remove the prop instead of hauling out?!
+1 good call
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Old 01-04-2010, 22:16   #22
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There are areas in Annapolis

"Home of the Sailing Hall of Fame"

That Divers will not go into......I think it is Spa Creek
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Old 01-04-2010, 22:37   #23
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I put a Galvanic Isolator on the Sea Ray and it did not do that much good...My stern drives were still getting attacked.

I had my 2 prop shaft zincs on the sail boat 60% eaten away after 3 months...and i was told that once they are about that far gone they really don't work that well any more...I could not believe how fast they were eaten up considering out of those 3 months i was only plugged in for maybe 3 days total...as i never left the dock with out unplugging.

Now this could have been an internal issue with the sail boat as it was new to me and prior to my complete rewire, as we did find some funky things....but the Sea Ray was professionally checked out and up to snuff.

I think there is more marina electrical issues out there then admitted to.
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Old 02-04-2010, 00:17   #24
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You wrote that you need to "load balance". Does that mean you have more than one phase or more than one cord?.
No, I meant that if I ever install air conditioning, even 6.5kW of power will not run it, unless it has that balancing controller that starts the units up at different times.

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There are more options; we have a smallish (12V 50A) charger that galvanically isolates line input from DC output and you could use something similar outside of your normal shore power system, without connecting it or bonding it to ships ground.
I thought about that. But then, I would get the same effect by just taking a wire clipper to the ground wire, wouldn't I? I would just be bringing power on board which is essentially unprotected by any kind of ground.

The more I read these horror stories, the more I think to just unplug.
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Old 02-04-2010, 02:39   #25
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DH, couple of thoughts, it's difficult to tell from the photos but were is the shaft anode?

Also what is the P bracket like? is it the same? or if its not as bad why is that? I don't have an answer to that question, but might be worth thinking about.

Pete
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Old 02-04-2010, 05:39   #26
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DH, couple of thoughts, it's difficult to tell from the photos but were is the shaft anode?

Also what is the P bracket like? is it the same? or if its not as bad why is that? I don't have an answer to that question, but might be worth thinking about.

Pete
Hi Pete: no shaft anode as delivered. The shaft is bonded into the bonding system and thus connected to tne big hull anode. Why didn't the bonding system protect my prop? It should have. The hull anode was well wasted but still a few pounds of zinc left.

P bracket is antifouled and seemed to be in perfect shape.
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Old 02-04-2010, 06:35   #27
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It is a semi-conductor that is isolating ground and one property of semiconductors is that under certain circumstances they will conduct. Most modern galvanic isolators will "re-connect" ground when the potential difference is 1.4V or more. That voltage is the sum of DC + AC voltage, for example 1.0V AC plus 0.4V DC. The damage on your prop indicates a bigger fault than that so the galvanic isolator might not protect at all.
Put two galvanic isolators in series....???
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Old 02-04-2010, 06:48   #28
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Put two galvanic isolators in series....???
I am still having trouble understanding what is bad about galvanic isolaters.

As Nigel Calder says -- all this is about protecting the boat versus protecting human life. If the galvanic isolator works as it is supposed to, then human life is protected by the circuit closing in case of a real AC or high current fault, connecting the boat's ground to the shore ground. The boat is protected by leaving the circuit open, disconnecting the boat ground from the shore ground, and interrupting the path of low-amp typically DC leaked currents which eat propellors.

If there is an open circuit fault of the galvanic isolater, which puts people at risk, then there will be an alarm to warn me that electrical equipment on board is not grounded. This seems to me acceptable.

If there is a closed circuit fault of the galvanic isolater, which puts the boat at risk, then it's not worse than what I have right now anyway.

I actually thought of two galvanic isolaters too -- but in parallel, not in series. That way, an open circuit fault of one will be resolved by the other, giving fail-safe protection of people.

If I'm not understanding something, I would be grateful for someone enlightening me.
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Old 02-04-2010, 07:07   #29
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This galvanic isolator system looks quite good:

Products :: Galvanic Isolation :: ProSafe DELUXE 50 AMP Single /30 AMP Dual AC Line System w/ 1 ea P/N 22066

It is self-testing, and will also test shore ground, polarity, and potential of the bonding system. It has a remote panel you can put at the nav table, and sounds an alarm in case of any fault, not just in the isolator, but a fault in the shore ground, etc. It is even capable of testing your zincs (you need to dedicate a through-hull to that sensor, however).

It is quite compact and only costs about $400. Seems a much more comprehensive and sensible solution to electrolytic corrosion, compared to the $2,000 isolation transformer.
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Old 02-04-2010, 07:25   #30
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Hi Pete: no shaft anode as delivered. The shaft is bonded into the bonding system and thus connected to tne big hull anode. Why didn't the bonding system protect my prop? It should have. The hull anode was well wasted but still a few pounds of zinc left.

P bracket is antifouled and seemed to be in perfect shape.
Thats got to be worth a 10 minutes check with a meter to see if there is a good electrical connection between the anode stud on the inside of the boat and the prop shaft.

You are assuming that it's shore power doing the damage, but could it be a 12 volt circuit? I am wondering (because I am not a electrician) how you could measure any leakage from the shore power circuit.

Pete
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