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Old 25-12-2011, 08:37   #16
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Re: Double Pole Breakers on Metal Boats?

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Originally Posted by Andina Marie View Post
On an aluminum boat you have to use insulated engine mounts and an insulated coupling to keep the ground from connecting to the hull (unless you have an isolated winding starter and alternator).
.
The best solution for an aluminium boat is to have the engine disconnected from ground.
This is not difficult to do. It requires an isolated alternator (many are anyway) and 2 wire senders.
There is no need for isolated mounts or starters. The engine is simply momentarily ground with a solenoid, during starting.
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Old 25-12-2011, 10:16   #17
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Re: Double Pole Breakers on Metal Boats?

Jedi, the discussion about double breakers revolves primarily around aluminum hull boats that have to be thoroughly protected from electrolysis. The worst electrollysis occurs when the boat is connected to shore power. Safety rules require the DC negative to be joined to the AC shore power negative. If the DC negative is also connected to the hull there is an electrolysis path from the hull surface to the dock ground that will cause electrolysis from stray and induced DC currents.

To break that circuit they try to make sure the DC negtive is not connected to the hull. Despite the insulated hose on the raw water (which often is not because it has a steel coil wire in it) the engine is connected to the hull by the salt water inside that pipe.

You can't insulate them while the engine is running but usually you are not on shore power when the engine is running so you don't need to. But at the dock current can flow from DC negative to the engine block to the water pump">raw water pump, through the salt water to the through hull and to the hull. It is true that "some" of that DC current flows out the center of the through hull hole and directly into the sea but a large percentage will be incontact with the through hull and the hull outside in the immediate vicinty.

So you have an electrolysis probem primarily around the through hull, and secondarily where stray currents that entered the hull at the raw water intake are leaving/entering the rest of the hull.

Water doesn't have to be flowing in the raw water hose with the engine runing for conduction to occur, the sea water is quite a good conductor. That is the reason for a plastic shut off valve to disconnect the electrical path through the water while at the dock.
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Old 25-12-2011, 10:23   #18
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Re: Double Pole Breakers on Metal Boats?

Andina,

Sorry, but my point of view is the EU one and that is that DC negative is not connected to AC ground and not to the hull. Also, for aluminum hulls, an isolation transformer and galvanic alarm is mandatory IMHO.

This prevents the problems 100%.

Also, the steel wire in a hose is encapsulated by the hose materials which insulate. When the raw water pump stops, their will be no contact through salt water either as an air bubble with slight vacuum will form within seconds.

cheers,
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Old 25-12-2011, 11:12   #19
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Re: Double Pole Breakers on Metal Boats?

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Originally Posted by DeepFrz View Post
-DC is connected to the hull of a metal boat in one place, and one place only.
Do you have a reference for this? I have read numerous times a floating DC system is what metal boats should have.
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Old 26-12-2011, 14:21   #20
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Re: Double Pole Breakers on Metal Boats?

The easiest solution concerning grounding through the engine is to install an isolating switch in the negative to the engine. When the engine is not running it is not connected to either negative or positive.
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Old 26-12-2011, 15:04   #21
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Quote:
Originally Posted by Andina Marie
Jedi, the discussion about double breakers revolves primarily around aluminum hull boats that have to be thoroughly protected from electrolysis. The worst electrollysis occurs when the boat is connected to shore power. Safety rules require the DC negative to be joined to the AC shore power negative. If the DC negative is also connected to the hull there is an electrolysis path from the hull surface to the dock ground that will cause electrolysis from stray and induced DC currents.

To break that circuit they try to make sure the DC negtive is not connected to the hull. Despite the insulated hose on the raw water (which often is not because it has a steel coil wire in it) the engine is connected to the hull by the salt water inside that pipe.

You can't insulate them while the engine is running but usually you are not on shore power when the engine is running so you don't need to. But at the dock current can flow from DC negative to the engine block to the raw water pump, through the salt water to the through hull and to the hull. It is true that "some" of that DC current flows out the center of the through hull hole and directly into the sea but a large percentage will be incontact with the through hull and the hull outside in the immediate vicinty.

So you have an electrolysis probem primarily around the through hull, and secondarily where stray currents that entered the hull at the raw water intake are leaving/entering the rest of the hull.

Water doesn't have to be flowing in the raw water hose with the engine runing for conduction to occur, the sea water is quite a good conductor. That is the reason for a plastic shut off valve to disconnect the electrical path through the water while at the dock.
Not correct. On an aluminium boat AC ground and dc neutral should never be connected Aluminium boats need isolating transformers. This solves t he problem. As to DC negative, best practice is an floating engine block. Not difficult to do. Double pole DC breakers help, they are not needed on a purely electrical circuit reasoning. But the help isolate unused DC negative circuits from the central negative system which can be carrying large transient currents.

Dave
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Old 26-12-2011, 15:25   #22
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Re: Double Pole Breakers on Metal Boats?

Quote:
Originally Posted by DeepFrz View Post
-DC is connected to the hull of a metal boat in one place, and one place only.
Do you have a reference for this? I have read numerous times a floating DC system is what metal boats should have.
It looks like I may have to change my attitude on this. I'm not sure where I read it but I think it must have been in the ABYC guidelines.
I could not find it in the old ABYC E-11 section that I have, although I didn't do an exhaustive search.

I see that Michael Kasten recommends that the hull be completely isolated if possible, however he also states that the hull should be bonded if you have a "highly complicated electrical system" (not sure what that means). He says that the isolated or non-bonded hull goes contrary to ABYC recommendations. I think I would follow Michael Kastens recommendations rather than ABYC in this matter.

Corrosion Prevention
Quote:
Aboard a metal vessel, the ideal would be to make use of a completely floating ground system. In other words, the negative side of the DC power will not permitted to be in contact with the hull nor any hull fittings, anywhere. With a floating ground system, a special type of alternator is used which does not make use of its case as the ground, but instead has a dedicated negative terminal.
This may however be a safety issue that I'm not qualified to comment on.
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Old 26-12-2011, 15:28   #23
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Re: Double Pole Breakers on Metal Boats?

I agree that any metal cruising boat needs an isolation transformer or isolation transformers.
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Old 27-12-2011, 22:02   #24
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Re: Double Pole Breakers on Metal Boats?

Everyone, thank you for your help.

I'd like to add the 'DC negative is shorted to the hull' meter that is mentioned, that Ovni's have fitted as standard equipment. I can't find one on Google-- I think I have the wrong words. Does anyone know what this is called, or know a manufacturer?

I'm guessing that it's just a very sensitive ammeter between the DC negative and the hull, with a fuse so that the ammeter doesn't get blown if a large short is made. And then an indicator light or alarm to show that the fuse is blown. I guess I could also make this, but there may be some detail in here that I don't get and would feel better just buying one. It'd be cool if it also detected AC ground connected to the hull, or even battery positive. Any case where the hull is no longer floating.

I'm looking into adding a silver/silver-chloride cell and galvanic corrosion meter to measure the electrical potential of the hull, as delivered by the zincs. Though I am thinking that as long as the zincs are not horribly eaten away, this meter may be quite boring.
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Old 28-12-2011, 04:33   #25
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Quote:
Originally Posted by msponer
Everyone, thank you for your help.

I'd like to add the 'DC negative is shorted to the hull' meter that is mentioned, that Ovni's have fitted as standard equipment. I can't find one on Google-- I think I have the wrong words. Does anyone know what this is called, or know a manufacturer?

I'm guessing that it's just a very sensitive ammeter between the DC negative and the hull, with a fuse so that the ammeter doesn't get blown if a large short is made. And then an indicator light or alarm to show that the fuse is blown. I guess I could also make this, but there may be some detail in here that I don't get and would feel better just buying one. It'd be cool if it also detected AC ground connected to the hull, or even battery positive. Any case where the hull is no longer floating.

I'm looking into adding a silver/silver-chloride cell and galvanic corrosion meter to measure the electrical potential of the hull, as delivered by the zincs. Though I am thinking that as long as the zincs are not horribly eaten away, this meter may be quite boring.
The meter you ask about in the first paragraph, is the one you describe in the last paragraph

ciao!
Nick
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Old 28-12-2011, 06:05   #26
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Re: Double Pole Breakers on Metal Boats?

Quote:
Originally Posted by msponer View Post
Everyone, thank you for your help.

I'd like to add the 'DC negative is shorted to the hull' meter that is mentioned, that Ovni's have fitted as standard equipment. I can't find one on Google-- I think I have the wrong words. Does anyone know what this is called, or know a manufacturer?

I'm guessing that it's just a very sensitive ammeter between the DC negative and the hull, with a fuse so that the ammeter doesn't get blown if a large short is made. And then an indicator light or alarm to show that the fuse is blown. I guess I could also make this, but there may be some detail in here that I don't get and would feel better just buying one. It'd be cool if it also detected AC ground connected to the hull, or even battery positive. Any case where the hull is no longer floating.

I'm looking into adding a silver/silver-chloride cell and galvanic corrosion meter to measure the electrical potential of the hull, as delivered by the zincs. Though I am thinking that as long as the zincs are not horribly eaten away, this meter may be quite boring.
silver/silver-chloride cell

There are really 3 ways to test

1. An electric meter. You will have to google it. Try looking in French there are a lot more French aluminium boat. Our is listed as “Testeur Fuite”
2. silver/silver-chloride cell
3. Galatest electrode
Galvatest | check the efficiency of your anodes...
This company has tried to produce a cheaper easier to use ˝ cell. It works well.


Disclaimer I did some work for galvatest a couple of years ago.
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Old 28-12-2011, 14:04   #27
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Re: Double Pole Breakers on Metal Boats?

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Originally Posted by s/v Jedi View Post
The meter you ask about in the first paragraph, is the one you describe in the last paragraph
Ah, then I really don't understand what is going on. I did not think that the half cell would tell you if the DC negative is connected to the hull... Back to reading.
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Old 28-12-2011, 14:26   #28
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Re: Double Pole Breakers on Metal Boats?

Sometimes I amuse myself by running all over my boat with a digital multimeter and taking measurements of the voltage difference between this and that.

It never seems to mean anything, but does remind me to keep the anodes fresh.
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Old 28-12-2011, 14:35   #29
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Quote:
Originally Posted by msponer

Ah, then I really don't understand what is going on. I did not think that the half cell would tell you if the DC negative is connected to the hull... Back to reading.
I think it is best if you contact a representative of the manufacturer of the half cell and ask for recommendation of who can install it for you. This is not easy as normal DC.

A quick check between DC negative and the hull is done with a multimeter in resistance mode.

cheers,
Nick.
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Old 28-12-2011, 15:00   #30
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Re: Double Pole Breakers on Metal Boats?

Quote:
Originally Posted by msponer View Post
Ah, then I really don't understand what is going on. I did not think that the half cell would tell you if the DC negative is connected to the hull... Back to reading.
Have a look at the Galvatest website it has some good general information.
Galvatest | check the efficiency of your anodes...



Disclaimer I did some work for galvatest a couple of years ago.
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