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/showthread.php?t=12024&highlight=cathodic+protection

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

http://www.samsmarine.com/forums/showthread.php?t=5177&highlight=cathodic+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???

 

[REBrueckner]

rsmith,captddis:

Boat manufacturers bond everything as far as I can tell because that is what ABYC still recommends; that's what surveyors seem to follow. And for fiberglass boats, it makes little difference except for the risks I posted above. Aboard my own Hatteras, for example, everything except transducers was bonded and I left it that way.

There is no reason to disconnect existing bonding aboard any fiberglass [Hatteras] hull unless you think the risks I posted are too high. And I would keep all bonding on any far east hulls with far east alloys.....especially from the 1960's and 70's. I have read and heard from several sources, but don't know first hand, newer alloys are more uniform, better quality.

Crevice corrosion was a problem on some older far east boats but I have not followed any of that for years. Bonding them will not prevent that type of corrosion but can mitigate it to some minor extent.

If you whack a thru hull lightly with a hammer and it doesn't break, likely you are good to go. You can also test props that way by listening to the "ring"..a solid prop sounds something like a slightly muffled bell, a corroded prop may still look fine but will "thud" more than "ring".

 

[captddis]

Again we are discussing Hatteras Yachts, not Taiwan boats etc. You just said to leave the Hatteras bonding alone. Therefore the ducers should be bonded also!!

 

[rsmith]

Your waaay off base here REB You shouldnt be handing out bad advice. There is plenty of mis information circulating around the internet. Quoting it and taking it out of context dosent make it true or correct. Not bonding undermetal parts and depending on banging them with a hammer to test their integrity is just plain stupid. Your cut and past answers are akin to alphabetical dirareah and many times make no sence.

 

[sgharford]

What other methods can one use when testing structural integrity of thru-hulls other then whack with hammer? I have never seen this method (and only this method) used several times in miscellaneous past posts.

 

[REBrueckner]

Captddis

"You just said to leave the Hatteras bonding alone. Therefore the ducers should be bonded also!!"


I did not say that; I explained the pros and cons. That conclusion does not follow the statement. I clearly explained the pros and cons of bonding. If you are willing to accept the negatives, bond away!

As I posted, I would clearly bond a transducer on a fiberglass hull if that's what the manufacturer recommends. Not doing so might void a warranty.

"Again we are discussing Hatteras Yachts, not Taiwan boats etc...This is a Hatteras forum! They never made wood boats. Why waste space on wood practices???"


I put in a sentence or two about "other" boats to draw contrasts and clarify bonding issues. Some Hatt owners have multiple boats, and one owned and may still own a Matthews just like mine. He PM'd me to thank me for such a cathodic protection post quite sometime ago. Many wood boat owners don't know the details of proper cathodic protection and that's another reason why I am careful to draw distinctions between fiberglass, wood and metal hulls. Sorry, you'll have to read a few extra sentences now and then on this issue or just skip my posts if you prefer.


rsmith:

"Your waaay off base here REB You shouldnt be handing out bad advice."

What's "off base" and "what's "bad advice"....?? Can you pick something specific and we can discuss.

"There is plenty of mis information circulating around the internet."

NONE of this information came from the internet.... but some came from the 12 Volt Doctor's Practical Handbook, Spa Creek Instruments, Edgar Beyn; Your Boat's Electrical System Conrad Miller and E.S. Malony; Some from ABYC; Nigel Calder's Boatowners Mechanical and Electrical Handbook, and some from a West Coast manufacturerand corrosion consultant company ,,,,,of a silver/silver chloride corrosion test meter...can't remember the manufacturer name...looks exactly like the current PROMARINER test meter.

[edit: just remembered the last source Yacht Corrosion Consultants, Ventura California...their meter came with an excellent 50 page or so technical explanation and test procedures.]

" Quoting it and taking it out of context dosent make it true or correct."

example please?? and we can discuss. All the above sources and my suggestions are essentially consistent with minor variations.


"Not bonding undermetal parts and depending on banging them with a hammer to test their integrity is just plain stupid..."

Not what I said. Please read what I post and don't mis characterize them...
that helps no one.

I said anyone can test current [physical] integrity by moderately banging/whacking... there is no other convenient method. That's why surveyors regularly "sound" props. Are you unaware of this???
Never seen a surveyors "rubber mallet"....???

Even a properly bonded underwater metal part with adequate sacrifical zinc may be subject to crevice corrosion....stuff can literally fall apart due to alloy impurities even when properly connected electrically to a bonding system. And cavitation corrosion can also weaken props, especially prop tips that move at the highest speed. That will also change the ringing sound of a prop.

In addition props are NOT properly protected via a general cathodic protection system...that's why god invented shaft zincs and why they should be placed close to the prop. And why sounding props from time to time is a good move.

"Your cut and past answers are akin to alphabetical dirareah and many times make no sence."

Please specific and we can discuss!

////////////////
PS: You'll note the articles MikeP previosuly posted are generally consistent with my posts above. The first article he referenced does a good job explaining why that author recommends isolation of underwater parts.

 

[Boatsb]

I think someone is trying to say you have Diarrhea of the keyboard. I know I am able to google for myself and you do not need to do it for us. Is there a reason you need to post googled information on every subject that is discussed?


Remember according to wiki a while back Hatteras boats were 3 feet thick and nuclear powered. Do not believe everything that is on the internet and more seriously remember the difference between theory and reality.

 

[yachtsmanbill]

What other methods can one use when testing structural integrity of thru-hulls other then whack with hammer? I have never seen this method (and only this method) used several times in miscellaneous past posts.

Wasted brass/bronze is usually pretty evident buy the lead burning out leaving the copper, as noted by the pink outer wrapping. These are 1/4-20 bolts, unbonded, above water, through the wood spray rails, into fiberglass.
The other pic is a chrome plated bronze deck fitting fastened INTO fiberglass only. Drain weep hole was plugged leaving no where for rain AND seawater to leak from... ws

 

[bostonhatteras]

Nigel warren, in his very complete manual, states that if a 'bronze' through hull is isolated, meaning not electrically connected in any way then there is no need to bond it. Now this assumes a quality bronze fitting, WITHOUT ZINC IN THE ALLOY TO LEACH OUT. Any metal can be affected by GALVANIC corrosion, that being the alloy acting against itself or put another way, the alloy has an internal electrical potential. It depends completely on what the alloy is. Conversely ELECTROLYSIS is completely different. Electrolysis is stray electrical current literally moving metal from one place to another. Again if a fitting is truely electrically isolated, electrolitic corrosion cannot take place. So what do you do? Unbond and isolate? Or bond and protect with zinc. In the case of distant electrically isolated quality bronze fittings it is accepted practice to isolate them from the other fittings. In the case of an airmar transducer with a bronze fitting and plastic sounder fitted in the middle, personally I would be comfortable not bonding it to the ships bonding system.

As far as rsmith and captddis decrying Rebs posts, maybe they can remember this is an OPEN forum to exchange ideas. He clearly steps up to the plate and offers his OPINION while leaving it at that. The bandwidth that Rebs posts consume is a matter for the forum moderators, not individual posters. Anyone may skip over a reply if they so choose to do so. Personally I find rsmiths persistant criticism of Reb to be strange and distasteful. If anything has no place in this forum it is that.
Russ Robins

 

[REBrueckner]

Russ: "Any metal can be affected by GALVANIC corrosion, that being the alloy acting against itself or put another way, the alloy has an internal electrical potential."

exactly....That's what I have referred to as "crevice corrosion"....where impurities or a poor quality alloy eats away at itself. Cathodic protection systems do not protect against that internal corrosion.

Trying to summarize entire texts in a few paragraphs is not so easy; any critics are welcome to try to improve on my efforts.

 

[captddis]

Russ,
Since you named me, I will respond.
The OP asked if he should bond his transducers. It should not take more than a paragraph to answer the question. I answer based on my 35 years of working on boats professionally. I only answer questions that i have personal experience with.

Others never answer a direct question but just quote articles that they have read and always end with checking with the manufacturer, your surveyor, the insurance company, ABYC, NEC, Your Mechanic, ETC, ETC, ETC, AD NAUSEUM. What use is that and to take 3000 words to do it!

The disinformation on this forum is incredable!!! Someone will post a question about a current engine or Generator and others will give a long winded post about their 1966 model and all of the information given is incorrect.


I really don't see the benefit of answering a question with a bunch of useless fluff that only confuses the issue, But that is me..... YMMV!