Am I missing any zincs?

[Finnegan]

Other than the heat exchanger and prop shaft, are there any other zincs on the engine or transmission I should be concerned about?

Boat is a 26 cuddy and has a PCM 5.8 with a velvet drive transmission. The transmission has a fair amount of exterior rust on the case so it has me wondering.

 

[Ship]

I know there will be multiple opinions on this but I installed them on my trim tabs, shaft, rubber and had a bonding wire connected to a thru bolt on the rudder post, a wiper on the shaft on the interior which was bonded and thru bolt on the trim tabs. I know, a lot of craziness but have lost zincs by the middle of the season which is way to short a time. The cost of zincs is way cheaper than one of any of the metal parts that were bonded.

 

[Robert Daber]

My setup is similar to what Ship mentioned with the exception of a wiper on the shaft. I have zincs on my shaft, Trim Tabs and Rudder. The rudder is bonded inside the boat. The quality of the zinc is important too. I use a high quality zinc made in Long Island, NY by the company name B&S Marine Anode. You pay a few dollars more but there anodes outperform other brands not made is USA. Their anodes have lasted all season compared to other brands which I have used. So in the long run you save money.
There website has good information under FAQ.
www.bandszincs.com/

I buy the zinc here. https://marineengineparts.com/. Also located on Long Island,NY

 

[Mistress]

Tabs, shaft, rudder in the water. In the engine compartment, both engine and transmission coolers. I guess some tran coolers don't have provision for a zinc.

Mine running gear zincs are all CAMP from boatzincs.com. The didn't have the right pencil zincs.

 

[Flick]

Other than the heat exchanger and prop shaft, are there any other zincs on the engine or transmission I should be concerned about?

Boat is a 26 cuddy and has a PCM 5.8 with a velvet drive transmission. The transmission has a fair amount of exterior rust on the case so it has me wondering.

I don't keep my 26 in the water so I only have zinc on the rudder and fwc system

 

[pilarboat]

I had a very short term and part time business tracking down galvanic corrosion problems and creating solutions. We had a couple of jobs and just gave up. My partner in the business was a GA Tech electrical engineer; we sort of gave up because most people give galvanic corrosion very little attention until there is a complete failure of a metal part. So here are a couple of things to keep in mind and relate to some of the comments. The appearance of rust on the outside of the transmission is not an indication of "galvanic" corrosion and is nothing to worry about; you will be long dead before the rust gets beyond the surface of the trans case.

Galvanic corrosion is the immersion of dissimilar (different) metals in a salt solution. An electrical charge is created between the metals in contact with an electrolyte (salt water) and the electric charge thingies look for an escape route, that route being through the least noble metal. This is why your zinc erodes; it's magic cause that's where the electrical things escape and take the zinc along for the ride.

So an anode (zinc) is attached to one or the other of the different metals either directly or through a wire, and this is where the electrical charge escapes. When the charge escapes, it carries with it the minute particles of the least noble of metals (da' zinc). With no zinc to carry away the charge, galvanic corrosion magically occurs and your boat might sink. This is my pea-brain description.

A properly zinc'd boat will have a measurable electrical charge of between 500-900 mv. That's almost a volt of electrical current with the boat just sitting there.

How do you measure this? With a very expensive (about $200) silver-silver chloride testing wire that goes from your volt meter (ground) to the water alongside the boat. Ya' stick the positive wire probe to whatever you want to test, and wallah, you will get a reading. Wood boats should never be over 500mv and glass in the 850-900 mv range.

If properly bonded, all of the metal in your boat "should" have exactly the same electrical current (within 1-3mv), if not you have a potential problem.

With your boat in the water, all bonding is sharing the same ground to include your battery ground; when out of the water there is no common ground; confusing, yes, it confuses me but as I wrote, it is magical.

Here's a question: Is there a bond between the drive shaft/prop and the engine block? The answer is no because of the moving bearings, gears, and shafts inside the trans. Yes, the trans case has a great bond to the block, but not the innards. I ain't gonna argue about this, do it your way, bond the engine assuming your shaft and prop are bonded to the engine block and watch your prop fall off full of pit holes. This is the reason for having a shaft zinc that will erode at a different rate than say, the rudder zinc.

Have you fallen asleep yet; I am. There have been Phd dissertations written on the subject, none of which I can understand so this is the reason for my "pea-brain" description.

Want to confuse the little electrical thingies running around in your boat, then over-zinc it. Yes there is such a thing and creates more problems than it solves. I ain't goin' there, it's above my pay grade.

 

[Robert Daber]

Good explanation pillarboat. There tends to be some different opinions on where to use sacrificial metal like zinc however there are some basic rules to follow.
For galvanic corrosion to occur it must have these three conditions
1. Dissimilar metals
2. Metals must have electrical contact or in other works bonded to each other
3. Metals must be exposed to an electrolyte such as salt water

So an engine and transmission could have dissimilar metals so they meet number 1 and 2 but typically not 3 unless you have aluminum intake or heads in a RWC engine

So as an example of dissimilar metals, bonded and immersed in an electrolyte would be the shaft and prop. There is a galvanic scale which shows where metals stand but in the case of the shaft (stainless steel) and propeller (bronze) the shaft is the more noble metal (cathode) and the bronze prop is the active metal (anode). Electrons travel from positive to negative so the positive charge electrons on the bronze will want to travel to the cathode which is the shaft taking metal particles with it (pitting occurs). However since zinc is higher then bronze on the anodonic side of the scale the zinc becomes the more active metal saving the bronze metal on your prop.

 

[pilarboat]

Robert Daber:

You got it. Keep in mind that the inside of the transmission will have no contact with an electrolyte; if you have salt water in the trans, you have really serious problems. I know, I just bought a new trans. Given that the engine block is grounded somewhere, then the bell housing bolted to the block, then the trans casement bolted to the housing, everything is bonded and the inside of the trans does not need bonding.

BTW: To pick fly poop out of pepper; you mentioned that zinc is higher on a scale. I know where you are looking and the scale is actually upside down. You are looking at an ascending scale, not descending. It is safer to say that zinc is the least noble of metals. Picky, Picky.

Your response is spot on. Mike. PS: I see you are in Pt. Pleasant, I grew up in Cape May.

 

[Finnegan]

Guys, thanks for the awesome replies. You gave me a lot of good info on the subject.