galvanic on trasducer

[robymayway]

Hi friends!
I have a little question about galvanic corrosion.
I have just change the transducer of my garmin c2010 c with a new airmar transducer.
instruction sheet dosn't tell about connection the airmar transducer with antigalvanic circuit on the boat.
I call the airmar customer service and they tell me once again that it isn't necessary due to the tipology of manufacturing of transducer.
That sound crazy....
All owner of boat know very well what damage my cause the galvanic on metal placed under the water line...

what is your opinion about this matter???
Contrary they suggest to avoid to make any connection to avoid problems!!!!

thanks for your comments

[REBrueckner]

"Tipology".....what is THAT supposed to be??

None of my transducers have ever required connection to cathodic protection. I doubt most of the head of a transducer is metal. In any case, like an isolated thru hull fitting, connection to cathodic protection should depend on the metalurgy of the component, not hard and fast "rules". Was your old transducer connected?? I suspect not.

Follow the manufacturer's recommendations.

[rsmith]

All my xducers are connected to the bonding system so that the zinks get eaten first as the least nobel metal.

[robymayway]

"Tipology".....what is THAT supposed to be??

None of my transducers have ever required connection to cathodic protection. I doubt most of the head of a transducer is metal. In any case, like an isolated thru hull fitting, connection to cathodic protection should depend on the metalurgy of the component, not hard and fast "rules". Was your old transducer connected?? I suspect not.

Follow the manufacturer's recommendations.

Thanks REBrueckner!, I followed exactly manufacturer's recommendations.
My old bronze transducer ( fitted in original on 1981 )wasn't connected to the cathodic protection, now the new bronze airmar is placed exactly as it was the previous without cathodic protection.
My question was only to understand why all metal fitted on the HULL of a boat requiring a cathodic protection and the bronze transducer not required cathodic protection ??? why ???
May be an interesting thread...Rsmith wrote that his transducer is connected to the bonding system and he is satisfacted!!

thanks

[captddis]

I bond all transducers I install. Just because the old xducer was not bonded does not mean that the replacement should not be.

BTW, Anytime we sent an xducer up to Hatteras for them to install in a new boat, Hatteras bonded the xducer.

[REBrueckner]

I've posted about cathodic protection a number of times. I'll see if I can find a few of those. My comments always address salt water applications, fiberglass, not wood unless wood is specifically mentioned and never metal hulls (cause I don't know much about metal).

Cathodic protection is connecting underwater metals together via a bonding system to which a zinc cathode is also connrected: the more active zinc metal gives up it's electron preserving less active metals like thru hulls, shafts,rudders and props. Us quality (last 30-40 years or so) silicon bronze thru hulls (all Hatts) will last forever without bonding, but manganese bronze props and rudders do require cathodic protection. A cathodic protection system is inadequate, in general, to protect internal engine partys exposed to saltwater.

History
Cathodic protection grew in part from some misconceptions before the complete mechanisms were understood, when there were a lot of straycurrents in poorly wired marinas, and when metalurgy was not as precise as today. Inferior alloys from the far east continued largely unwarranted concers with US manufactured alloys and the transition from wood boats to fiberglass further entrenced traditional bonding/galvanic protection circuits. ABYC had been reluctant to change recommendations perhaps 20 years ago because old timers there had a lot of influence and most galvanic connections don't do any damage to fiberglass hulls.

Risks
Insurance companies,especially, have found that one of the negatives of such extensive bonding can occur when lightning strikes: thru hulls have been blown apart and boats sunk. I first studied galvanic effects because of delignification aboard a 1961 wood Matthews I owned: Bottom line is that boat had way too much zinc and the "protection" currents caused wood around thru hulls and shaft logs to soften. Other Matthews owners in the Matthews Boat Owners Association had noticied similar issues so I investigated and wrote for them how to prevent delignification of wood hulls.

Bonding systems to underwater metallic parts act as an antenna that connects underway stray currents to your precious metal parts; if zinc is present you'll be ok but those underwater currents cause zinc to eat away and when it does, the currents eat your underwater metal. An isolated thru hull for example, not connected, is immune to such currents. Similar story for a shore power cord not isolated from your boat.

Fiberglass hulls themselves are essentially immune to that stray current and galvanic protection current damage and so you can do pretty much what you want. And so are marelon type (synthetic) thru hull connections also immune from such currents..and from galvanic ciorrosion.

People buy a boat, see everything connected and that's what a lot of surveyors have been taught to look for, and so the traditional approach continues.

[REBrueckner]

Here is what I am talking about (from MikeP):

http://www.samsmarine.com/forums/sho...dic+protection

and here is another discussion with my views in post #6:

http://www.samsmarine.com/forums/sho...dic+protection

did not find my more extensive original posts....

[REBrueckner]

Found one in my computer files: (was also posted on Trawlers and Trawlering)


I recently posted the following on the Hatteras owners website...this is
informational and primarily for wood boat owners .......A search should
turn up prior posts on this subject. Delignification of wood simply means
that when even small electrical currents pass through wet wood, the ion
flow destroys some of the wood..lignin.... which leaves a weakened,
leaky,mushy,soft mash of remaining wood components. Most susceptible are
thru hulls where the interior is out of bilge water...shaft log wood
mountings are often susceptible for this reason.

Stray currents (leaking from improper wiring or poor insulation and
called "electrolysis" or stray current corrosion) and especially dc leaks
are SERIOUS and should be corrected promptly. AC leaks should be fixed as
well, but do not ruin metal and wood nearly as fast for comparable
current flows..

Another source of unwanted electrical currents through wet wood is zinc
protection: it can protect underwater metals and destroy wood at the same
time. Too much zinc: wood damage!!!! One solution is to reduce zincs
until just the minimum voltage is present to protect metals...usually
about 500 mv (1/2 volt) for common marine bronze relative to a
silver/silver chloride reference. Once delignification begins that likely
won't be enough to stop further wood damage: it's best to disconnect
bonding from isolated marine silicion bronze thru hulls...they will last
virtually forever. Beware older foreign alloys.

If zincs deterioriate and fall off, galvanic corrosion (current flow due
to different metals being immersed in an electrolyte (salt water)) can
commence and may also further deterioriate wood. A bonding system without
zincs is positively worse than no bonding system. No bonding wires is the
best protection for wood.

Another negative aspect to bonding: if there is stray current present in
the water, say from a poorly insulated dock electric line, the thru hulls
connected via bonding act as a big antenna and pick up the
voltage...current flows into the thru hulls and ashore via
ground....further deterioriating wet wood. If no bonding, no current flow
thru any thru hull and they are safe. Another potential effect of bonding
wires: a lightning strike may be directed to a thru hull and it literally
blows up from a strike...boat sinks...!!!!

Note that in general fiberglass boat bottoms are rather impervious to
normal galvanic current flows...not so wood.

[captddis]

REB,
You can C&P articles you read all day long! I use my eyes and experience.

I have seen many pieces of underwater hardware wasted and in need of replacement due to not being bonded. Meanwhile other parts on the boat that were bonded are in excellent condition.
The non bonding approach is usually used on wood boats and boats that are moored and not connected to marina electric.

If a boat has a bonding system, then EVERY piece of underwater hardware should be connected. The only exception are the trim tabs which are usually not bonded but have their own zinc.

[captddis]

You must be really bored. This is a Hatteras forum! They never made wood boats. Why waste space on wood practices???