Wow, you have made quite an effort to understand this problem. That's good,
but you are not there yet. First let see if I can explain the difference
between galvanic and stray current corrosion. Both are electrical corrosion
and the result is identical, but the causes are quite different.

Galvanic corrosion is caused by different materials immersed in an
electrolyte electrically connected. This will create a self induced
electrical current between the two metals, like little self charging
batteries. The strength of which is a function of the galvanic distance
between the two in the table of elements. As you can imagine, this can be
very difficult to eliminate. The only way to do this is to eliminate the use
of dissimilar materials and or electrically insulate the two. Like using
bronze fittings on a steel boat. Even homogenous alloys suffer from this
all on their own when submersed in water to different degrees. An example of
this is my recent experience with the boiler in my Saeco coffee maker. Saeco
has replaced the bronze boiler in their early models with a die cast
aluminum one in their newer ones. The die casting technique is to fill the
mold using molten metal under pressure, but in this case a large amount of
zinc has been used with the aluminum to promote molten flow in the mold.
This is great for production, but not for this product. Upon disassembly,
the inside of the boiler looked like worms ate holes all through the
casting.

Stray current corrosion is identical in nature, but is caused by an external
DC power source, like in the electroplating process. This type of corrosion
is the easiest to eliminate and the most likely culprit in your experience.
On boats, this is caused because the hull is being used as the ships
battery's return path for current and the safety ground for shore power is
also connected to the hull. Although stray AC current is somewhat unhealthy,
it is the DC current that does the damage. Since electrical code demands the
connection of safety earth, every boat connected to shore power becomes a
participating element in a current leak caused by any shore power connected
boat. That's where the liability case comes from. Now that you understand
the problem. Eliminating your vulnerability depends on your perspective. Are
you a boat or are you the marina? If you are the boat, you can use galvanic
isolators, which are essentially diodes. These inhibit, but do not eliminate
the problem from your neighbor because diodes have some internal resistance.
You can isolate your hull from the battery system and use an LED as a fault
indicator for your boat. (a good thing) You can elect to NOT connect the
shore safety earth and use an isolation transformer to magnetically couple
AC power to your boat and creating your own ships earth for your safety
earth, but that can be construed as illegal and against local electrical
code. The latter is the only way to eliminate the risk of someone else's
electrical fault from damaging your boat.

Now if you are the marina, you have a BIG problem, because you cannot
eliminate stupid in other people. You can make all the rules you want, but
stupid will prevail. I have no solution for this problem, I don't think
there is one. You can use plastic floats and other non-conductive materials
as well as insolate all uses of metal under water, but that's it.

Coming back to the system you mentioned, it does some isolation, but it is
primarily a detector, not an eliminator. It doesn't hurt, but I wouldn't use
it. On super yachts and commercial ships there are in use many automatic
systems that detect voltage imbalances throughout the vessel by the use of
many sensors and when detected, apply an opposite polarity impressed current
to counter any induced potentials. These are expensive systems, but they
work extremely well and pay for themselves over time. Very rarely do you see
anodes in use on commercial ships. They are simply too expensive and
maintenance intensive to use in the quantity required. They are a band aid
and by introducing a low nobility material to the equation, actually
encourage galvanic currents.
Steve


wrote in message
...
On Aug 3, 8:45 pm, "Steve Lusardi" wrote:
Angelika,
This system is relatively simple. It is primarily a detection system,
which
allows you, the owner to identfy the source of stray currents for
correction. Additionally, it provides a kit to isolate the engine's
connection from the battery to the hull. All of this is a good thing, but
it does not protect and it does not prevent electrical corrosion. It
facilitates YOU to do that.
This subject is extremely complex and cannot be fully addressed in a NG.
There have been numerous books written on this subject if you wish to do
the
research. Further complicating this problem is the act of inspecting the
observed corrosion cannot identify the cause of it. As the website states,
the cause could be either galvanic, stray current or both. Prevention must
start at the beginning of construction of the vessel and be continued
through the application of common sense and best practices throughout the
vessel's life-time. Properly executed from the beginning, these practices
will eliminate virtually all corrosion. Please also understand that anode
protection is a band aid, not a cure and consequently, be a CAUSE of
corrosion all on their own.
Steve

wrote in message

...

I recently found out about a new system that prevents boat corrosion.
The system is called SeaBis Electrolysis Corrosion Prevention System.
This system is apparently the first of its kind that detects and
eliminates stray current and actually prevents corrosion. Once the
system is installed and you have completed a process of elimination of
stray current coming from in and outside the boat, the boat is then
protected once and for all. Any new stray current is monitored and
when it turns up it is eliminated and the boat once again is
protected.

The system also comes with an anode voltage tester and prode to
measure the effectiveness of existing anodes. Anode lifespan is
prolonged up to 2 yrs with this system.

Is there anyone out there that has installed this system or has a
better or another way of preventing corrosion damage to boats?

More about the system can be found athttp://www.seabis.net

rec.boats.building

Hi Steve,

Thanks for that. I have gone into this at length and have discovered
that there is a lot of confusion around exactly what causes
electrolysis and what is electrolysis. What are the differences
between electrolysis and galvanic all of which has been explained and
researched on the web site. http://www.seabis.net.

In fact as I understand it galvanic corrosion is accelerated in the
presence of stray current and is slowed down when their is no stray
current. It can be also be slowed using galvanic isolators and anodes.

When you say it does not protect and it does not prevent electrical
corrosion have you tried the system and found this to be the case or
is this something you have come up with from reading the information
on the web site? If there is no stray current then there can't be any
electrolysis- right?

From where I sit if the system is able to do what they say ie

1. hard wire install the stray current detector ( open circuit engine)
2. follow their instruction manual on the process of eliminating all
the sources of stray current

My boat is now free of ALL stray current.

Then use the stray detecter on an ongoing bases as a monitor that
tells me when new stray current is present would prevent the boat from
experiencing any further electrolysis - so if I had any electrolysis
damage repaired and then install a SeaBis system, so long as I kept an
eye on the seaBis stray current detector regularly my boat would be
free of stray currently permanently.

Also I found that a technical marine engineer is able to identify boat
corrosion quite easily and is able to determine where the corrosion is
coming from if not sure.

The system is able to prevent electrolysis simply by the process of
elimination explained in their installation and repair manual. Of
course as a Do-It- Yourself System I would expect to either manual
make the effort to install the System myself or have my maintenance
guy do it for me.

When you say "It facilitates that YOU to do that" I almost get the
feeling that with your emphasis that there is something wrong in my
having to facilitate a part of the process. ?

One thing is for certain I agree with you when you say prevention must
start at the beginning of construction and be continued through the
application of common sense and best practices throughout the vessels
life-time. And would have to say that the installation of a SeaBis
would most certainly be good practice prior to a new vessel hitting
the water- that would be the best time to be clear of all stray
current . There is a sort of comfort in knowing that stray current
coming off other vessels and off marinas has no way of effecting my
boat once the SeaBis is installed.

I spoke to a marina owner in Adelaide Aus who trialed the system
because at his particular marina the depth and current flow of water
was such that it induced stray current rapidly and he was susceptible
to insurance claims and on going electrolysis repairs from his tenants
who constantly complained about paying for recurring electrolysis.
Once the Marina was fitted with the SeaBis Electrolysis Prevention
Maintenance System and he could prove the Marina was NOT necessarily
the main cause and that in fact the vessels were effecting one
another, he implemented a SeaBis check on all boats prior to them
entering the marina and recommends that a SeaBis System should be
fitted prior to mooring.

Those boats that show critical readings of stray current he declines
entrance to the marina unless they do something to fix the stray
current.

over a period of 12 months he has almost eliminated the stray current
electrolysis problem and saved himself and his tenants thousands of
dollars. More importantly he no longer has the battle of insurance
claims against the marina as the insurance company fully accepts the
accuracy of the SeaBis readings.

Naturally I think any boat owner in the know is aware that anodes are
only sacrificial and as you say a band aid solution - however when
anodes are monitored and replaced regularly they do the job quite
well, the problem occurs when one forgets to monitor them and as you
say they deteriorate to a level where they actually become a cause of
corrosion- again the SeaBis Systems caters for this.

As per my original question all I wanted to know is if their is any
other product similar to the SeaBis system that can assist in the
prevention of electrolysis corrosion and if anyone can provide a
simpler method to help fix this problem.

My problem is that I have to find a way to cover off on 40k being
spent to replace pontoons that have been corroded by electrolysis
(this has been proven) and I now am deciding to install a SeaBis to
prevent any further damage.