Electrolysis

[biltong]

Can anyone or everyone try and explain the process of electrolysis on yachts, especially when surrounded by other boats in a harbour. How will being connected to shore power via a battery charger affect the situation. I thought I knew the answer to this, but the more people I ask, the more answers I get.

[Springbok]

As Eskom power is up and down and the SWC may put Knysna in the dark you will have no problem in the lagoon
Clyde

[biltong]

Originally Posted by Springbok

As Eskom power is up and down and the SWC may put Knysna in the dark you will have no problem in the lagoon
Clyde

Thanks Clyde. I knew I could count on you, however, as you know, Eskom is so efficient that their electrical supply is available anywhere in the lagoon by plugging into the first avaiable oyster.
So the problem stands.

[Blue Stocking]

As I am sure you know, any two dis-similar exposed metal objects in an electrolyte, will generate DC current.
The number of ways in which it can take place is limited to the number of boats nearby, -1, yours.
No!- thats not true--cables on the bottom of the bay can be one side of the circuit as well.
We have a shallow bay here where the Trans-Atlantic cables come ashore, and the zinc plating on the mooring chains remains for less than a month.

[skipmac]

Well, as you have already figured out, metal corrosion in boats is not a simple subject and has multiple possible sources, from your boat, from your neighbors boats, from the marina or even underwater cables.

Maybe try to break it down into two main areas.

1. Two electrically different metals (one common example, mild steel and aluminum) touching or electrically connected and wet with an electrolyte (like sulfuric acid in a battery or salt water in your boat). The two metals react in the liquid and generate their own electric current (the principle of a battery). This current will eat away one of the metals, in this case the aluminum.

This process can take place independently of any boats around you. The solution is to prevent different metals from touching or put another metal in the system (like zinc) that is eaten away more easily.

2. Currents from electrical systems.

Boats today can have complex electrical systems AC and DC which get more complicated when connected to dock power sources and, through the water, to the electrical systems of boats nearby. This can allow currents to flow from one place to another: within one boat, from one boat to another, between boat and dock, boat and water/ground. The currents are caused when there is an electrical difference between any of these.

An example. One boat is well grounded, another boat nearby is not and has electricity from a bad wire leaking to the prop shaft so current can flow between these two boats and eat away the most sensitive metal, often a bronze propeller.

The common way to deal with this is to electrically separate your boat from the surroundings by installing an isolation system. An isolation transformer is considered by most to be the best option.

Hope this is what you were looking for.

Skip

[biltong]

Thanks Slip. This is exactly what I have been after. Now more about the isolation transformer if you please.

[biltong]

Sorry SKIP, my slip

[skipmac]

Isolation transformer installs in your boats electrical system. Power from the dock is connected to your boat through the transformer but not directly. The shore power is electrically isolated from your boat.

A transformer in simple terms is two coils of wire close together but not connected. When you run an AC current from the dock through one coil it produces a magnetic field that crosses the other coil and makes current flow through the other coil to the boat. So you can pass power through the transformer but the in and out sides are isolated from each other.

Provides corrosion protection and protection from shocks.

[skipmac]

Originally Posted by biltong

Sorry SKIP, my slip

No problem. I've been called worse.

[ConradG]

The isolation transformer only sepperates the "hard" connection of the green wire when plugged into shore power. This does help negate the battery scenario by removing A contact between you and other boats connected to the same green wire...but you can be connected in other ways...Here we get into the issuse brought on by common techniques to do just the opposite of isolation, mainly bonding... And I will back out here and watch the sparks fly...Remember, your metal just being in the electrolite (salt water) is part of the battery and any less noble metal will give up it's electrons for the cause, especially when boded!
And then there's the whole other subject of stray electricity...

With aluminum hulls some of us desire to isolate any dissimmilar metals (engine and propshaft for instance) and use only metals that are close on the galvanic scale for direct contact like mild steel or galvinized and no stainless. On the dc system we also totally isolate the electrical ground from the hull returning everything to the neg terminal. Some of us stay away from ac power on the boat altogether because of the safety concerns of having an ungrounded conductive environment with a form of power that will kill. And, of course, some of us stay way away from marinas where there are all kinds of electrical systems in all kinds of repair states and even without the electrical systems, all those pices of stainless, bronze, etc sitting in close proximity in an electrolite makes your boat part of a battery regardless!
Zincs can help.

But who wants to be in a marina anyway?

[skipmac]

Originally Posted by ConradG

The isolation transformer only sepperates the "hard" connection of the green wire when plugged into shore power. This does help negate the battery scenario by removing A contact between you and other boats connected to the same green wire...but you can be connected in other ways...Here we get into the issuse brought on by common techniques to do just the opposite of isolation, mainly bonding... And I will back out here and watch the sparks fly...Remember, your metal just being in the electrolite (salt water) is part of the battery and any less noble metal will give up it's electrons for the cause, especially when boded!
And then there's the whole other subject of stray electricity...

With aluminum hulls some of us desire to isolate any dissimmilar metals (engine and propshaft for instance) and use only metals that are close on the galvanic scale for direct contact like mild steel or galvinized and no stainless. On the dc system we also totally isolate the electrical ground from the hull returning everything to the neg terminal. Some of us stay away from ac power on the boat altogether because of the safety concerns of having an ungrounded conductive environment with a form of power that will kill. And, of course, some of us stay way away from marinas where there are all kinds of electrical systems in all kinds of repair states and even without the electrical systems, all those pices of stainless, bronze, etc sitting in close proximity in an electrolite makes your boat part of a battery regardless!
Zincs can help.

But who wants to be in a marina anyway?

All totally valid and correct. The subject is much more complex and involved than my explanations and there are certainly many strategies and opinions on the risks, benefits and effectiveness of isolation, bonding, grounding, metal combinations, etc.

From the tone of the original question my assumption was that this very complexity is what has confused the questioner and so was trying to give a simplified explanation that hopefully would get him a basic understanding of some of the essential elements of the issue. To fully address the corrosion issue in detail is the subject of many books and could be a career in itself.

Unfortunately necessities of real life do force some of us into marinas, hopefully not for long.

[cdennyb]

I'm curious about this situation...
any experts? Say you have a fiberglass hull, (most are) and want to isolate the prop from that corrosion problem. Is it possible to isolate the engine from the electrical system completely? Use rubber mounts, no metal contact with the electrical system, alternator is run to a power inverter which is isolated, the controls and hoses and other brackets, etc. can be thru rubber isolation mounts, etc. and not have the prop be in the circuit.
That would leave the thru hulls left. Curious how far the isolation thing could be taken.

[GordMay]

Originally Posted by cdennyb

... Is it possible to isolate the engine from the electrical system completely? ...
... Curious how far the isolation thing could be taken.

No - not completely; nor far "enough" (to be useful).

[skipmac]

Isolation, bonding, etc. One of those areas where you ask 4 different experts you end up with 5 different opinions. I fall into the undecided camp on much of this.

[ConradG]

As for isolating the engine, it is ussually on isolating mounts and if penonlic bearings are used the electrical connections are the only thing directly connecting it. These can be of isolated ground construction, both starter and alternator(s) and special warning and tach sending units used... But, the close proximity of the different metals like props, shafts, through hulls, in a conductive medium.....Best in my opinion is to use the darn thing as little as possible and work towards the day of profficiency when you can crowbar it over the side and isolate it once and for all!
Seriously, there are bennefits to isolating it electronically that can't be ignored by some of us with metal hulls. Although I believe any metal problems below the waterline, even on fiberlass hulls, would be potentially disaster. so can lightening strike without a bonded and grounded underwater metal system on that fiberglass boat (vs the grounded metal hull which will potentially dissipate such energy on it's own...It is a complicated subject but there are also pretty well difined accepted practices for all but metal hulled boats where the jury still seems "out".