Galvanic corrosion on Brovo 111 outdrive 2004 342

[bottomline]

 Does anyone know if Galvanic Isolators  were standard on  2004  - 342  with B111   and where they may be located

[merwin10]

Hi

Been away from this for a while but never known Rinker to install a Galvanic system in the true sense of the subject to many $$$$$! They did offer a MerCathode® active corrosion protection on b3 engines, is this what you are talking about?

Mike -

[bottomline]

 Hi Mike
 This isolator is on the shore power negative groung,diod setup

 Thanks

 peter

[alswagg]

The Isolators are built into the electrical system for the A/C voltage.  All shore power supplied boats built from 1995 on have this built into the system standard.  The isolators are located near the main panel circuit breaker.  Al

[merwin10]

I guess I would have to see the schematic to figure out how a diode is going to provide Galvanic isolation. I am an electrical engineer (retired), we must be talking about two different types of isolation!

A single diode is not going to give protection for isolation. A diode bridge such as the one below, would provide some protection but is prone to malfunction if there is any problems or spiking on the AC line!


            |-----|<-----|<----|
    ------|                         |---------
            |----->|----->|----|
    
This bridge goes in-line with the earth lead between the shore power plug on the quayside and the AC electrical system on the boat. Each diode in the isolator will drop around 0.6 volts before it starts to conduct. So 2 in series will require 1.2 volts before any conduction takes place. There are two diodes facing one way, and two facing the other way to enable AC fault currents to flow in both directions (thus tripping the circuit breaker or RCD).
 
This means that the galvanic currents (which are usually between 0.4 and 0.8 volts) which cause galvanic corrosion are blocked. They would have to exceed 1.2 volts in order for a current to flow. They never exceed this level due to the metals involved and the water. This is a simple method to offer some protection to prevent galvanic corrosion.

Obviously if any one of the diodes fails the system is not going to work! A simple method of checking them is separate them and with a volt meter you will get a reading (connection) in one direction and not in the other, just switch the leads on the meter around.

Keep in mind this is not real galvanic isolation, real isolation requires a transformer and control circuitry! It provide real isolation of the shore power from the boat!

In any case, galvanic isolation needs to left to the boat desigers and engineers to figure out!

Mike -  
 

[AlexisandChad]

Grabbing my EE books now. 

[merwin10]

Hi All -

Now as you probably already know the circuit I posted is a simple diode bridge! One of the major problems with this again is that we all tend to add electrical stuff to the boat that the engineers never thought about! Of course we want the best so we also make sure this equipment has the good ole UL approval on it! This is a long story of a dog chasing it's tail, becuase for every fix there is another issue with this circuit!

WELLLL! all this stuff will cause a problem for this diode circuit! You see one of the UL specs is to reduce RFI (Radio Frequency Interference)! Most equipment today (tv, radio, cd player, microwave, VCR and the list goes on and on) have what is call switching power sources or supplies (convert 120v to whatever the unit requires). In an effort to reduce any RFI the power supplies are capacitive coupled to ground thus reducing the RFI. This poses a problem for our little diode circuit! as the combined voltages of this coupled to ground will exceed the 1.2volt trip of the diode bridge. The other concern it the high frequency of the coupled RFI. In layman terms the amount of times the voltage swings positive and negative. This high duty cycle RFI voltage will cause the diode bridge to conduct most of the time! Thus negating it as a galvanic isolator! It is like the diode bridge is not even there so no galvanic protection! Of course when do we need the protection, when in port tied to the 120volt shore power! What are we doing of course PARTY TIME! all of those switching power supply goodies are running putting there RFI on the line thus negating the galvanic protection the diode bridge provides! the only thing we can hope for is that during the week when no one is around there won't be so much RFI and the galvanic protection will work! One of the larger issues is the ability to pass of this RFI and voltage from boat to boat!

Now there is one other issue that is of concern here and it is just the nature of the beast! The so called ground is not really ground or zero potential between real mother earth and the green ground wire! If you took a grounding rod drove it into the ground and measured from the green wire to this ground rod you will see a voltage. One way this voltage gets on ground is that it is induced by the long runs from the actual ground of the service and your end of the wire. Think about it in some case that could be several hundred yards of wire that is changing direction 60 times a second of course there is going to be mutual inductance. So back to our little diode bridge that is going to turn on conduct at 1.2volts. Well lets say the ground wire has 3 volts on it! Yep you guess it no Galvanic Isolation! Now to help this issue the designers have a bonding system they connect to the Zincs in salt water and magnesium in fresh water on your boat in hopes to neutralize any voltage on ground (green wire) trying to achieve zero volts thru the water! This also acts an collector of stray voltage if a guy two boats over has a electrical issue his issue will erode your zinc or magnesium grounding system.

This is an imperfect solution for galvanic isolation the only real way to provide this isolation is through a guarded transformer which simply stated regenerates the boats AC locally on the boat! There is no physically connection electrically to the dock power! This transformer adjusts for low dock voltage and the guard shield prevents any stray voltages RFI or otherwise! The output is adjusted to provide perfect voltage regardless of the input!

Please remember this is only part of the story as there is another side to this DC voltage! This becomes a real issue if you use SSB radio (ship to shore)!

So now you know why my first statement was that Rinker has never provided true galvanic isolation because of the $$$$$$.

Mike -

[fmrosell]

The Isolators are built into the electrical system for the A/C voltage.  All shore power supplied boats built from 1995 on have this built into the system standard.  The isolators are located near the main panel circuit breaker.  Al

Is there any label or indicator to tell me where it is and what it looks like?

I want to see it...

[merwin10]

Hi -

Depending on the exact model it is in different locations! I believe Al said it was near the main breaker in the panel but could be anywhere in the circuit! There is nothing really to see or do! I guess you are one of those guys that want to know all about there boat! That is meant in a positive way!!!!! I commend any one who works on their own boat and knows all the systems! This becomes a SAFETY issue if something happens out on the water!

Mike - 

[AlexisandChad]

So.... I have a 1993 and have a Guest Isolator and Charger, yet there is a smaller box with all my grounds/negatives going to it (#2 gauge) and I was assuming that was just the negative isolator. I would not think it was a Galvanic isolator as I was on a team that installed on on a 108 Lazzara and that systems was in the high, HIGH 5 figure range.  As Mike said, the only way to truly achieve galvanic isolation is to have your personal transformer where all your current, either positive or negative, is handled by that one source. 

[merwin10]

Hi All -

Ok now that I have done the dump on Galvanic Isolation more than you ever wanted to know! Any Questions????

Mike -

[fmrosell]

Ok now that I have done the dump on Galvanic Isolation more than you ever wanted to know! Any Questions????

Mike -

...yes. there is still no consensus (on the internet sources I have looked up) on whether the concept works or not....all I can say, on my part, is that according to Al, there is a built in isolator on the AC circuitry of Rinker boats after 1995.  I had some serious alectrolysis on my stainless props and trim tabs.  I installed an isolator, bonded the tabs, filled-repaired-painted the props and moved the boat to another marina....for the past four years, no new corrosion issues...but I don't know what fixed the problem...

[ParkRode360]

I've really missed Mike's solliquies!!! Welcome back, Mike!

[merwin10]

Yea well here is a soliloquy that will shed some light on the complexities of the situation! The problem may not be your boat or other boats in the marina or even the marine!!!!!

At the east end of the Cape Cod Canal there is a marina that a few fishing buddies keep there boats! A little further down the canal is the Cape Cod Power Station! Now these friends of mind were going thru a 2 pound zinc in a month! These zincs should last all season! They chased their tails around this issue blaming each other the marina on and on! So they asked me to come down and take a look see! I ran a wire from the power ground stake (mother earth) to a zinc on a cable and threw it in the basin! Measured between the zinc and mother earth and saw voltage! Obviously someone was leaking into the water but which of 100 boats! After further investigation I could not isolate a single source for the leakage I was seeing! Fortunately each dock head had a ground stake but I did notice that the further I got from the canal inland the voltage seem to dissipate.

So I went up to the head of the marina opening into the canal and the voltage increase but the boats were now further away! It was then that I noticed the canal at the east end had a steel bulkhead that went all the way past the power station! Just of the hell of it I measured between the steel bulkhead and the ground stake WOW! What I got was about 40volts. Didn't make much sense but we went for a walk and closer the the power station the voltage would be fluctuating depending on the steel panel I measure from!

I when to the power station and reported my findings that they seemed to be leaking voltage into the water and causing the problem! The station management came out with their engineer and I showed them my findings! About a month later the power station drove ground rods every 50 along the steel bulk head and attached the other end to the bulkhead itself!

Well after that there 2 pound zinc lasted the whole season and now there is a preventive maintenance schedule to test the grounding of the bulkhead twice a year!

Now one interesting fact there was one boat a 60 foot Hatty SF that had no issues with Galvanic erosion! Talking to her captain I found out that the Hatty is equipped with its own on board Isolation booster transformer! Ah no wonder you never noticed the problem!

So you see your problem could have been something benign as that situation was! There is no telling what caused it just be happy it did not follow you!

Mike -

[raybo3]

Mike great info here. We have a problem at my yacht club and I have not had a chance to test it yet. Going to do it this summer. Great post!!!