The Mystery of Zinc's

[Helmar]

Who can help answer the mystery of Zinc's
For outboards, how to do know when enough is enough?
Can you have too many or too large of a zinc installed?

One percent of What ??

I know Merc's have there own, Zinc and aluminum.
I know of you Mix them, one will cancel out the other.
But how to do you know what and where should you mount them?

Do we have a rule of thumb here?

[Tim_Mattson]

Joe ,
Basic chemistry taught me that all elemnts try to trade places with the nearest neighbor,with it slowly degrading until it is basically half of both parties involved,with some extras coming from the seawater.
They do sell two types ,one has magnesium and is for freshwater use(at least I remember it that way....).
The houseboats used to cover the hulls with Zincs and had no motors so it set off a corrosion bomb on every hull around.
You do want to see 10-30% go away each year and if not going away at all,then you may have too much of it.
Outboards use little ground wires to balance the charge on pcs isolated by rubber or seals.Any exposed alum can become your Zinc.
Leave one part ungrounded and you`ll soon see it become the Zinc.
The newer motors even have internal zincs hidden inside behind T-stats.
You want some on both the main motor and on the hull,but never so much they don`t ever corrode.
Mt white 70 hp on the Seafair had a broken ground which made the mid-section paint go away,ddin`t find until I lifted the powerhead to reveal the broken end....Done at the factory!
Any boat with Electric start Kicker also needs some checking and watching to make sure the battery wiring is sharing a common ground.
Tim M
ps 1 % may be of Mass......1/3rd eaten away yearly is a good goal.

[Wally]

We had a 90 HP Force. The motor wouldn't tilt up far enough to get the whole LU out of the salt water when it was on the buoy but the internal zinc was out of the water. The part in the water started to pit.

I hung a piece of zinc off the transom and attached it to the Force with a piece of copper wire (which corroded).

After a couple years of this, I noticed the motor transom clamps had split vertically. A Force mechanic had never seen it before. I think my "fix" caused it.

Anyway, I think the amount, surface area, placement, etc. is pretty critical.

[McSkagit Tim Jones]

Zincs (Sacrificial Anodes)

Any time you immerse two dissimilar metals in an electrolyte you create a battery. In the case of underwater boat hardware, lower units, etc. immersed in seawater (the electrolyte) you create a battery. Sea water is full of sodium and many other free ions, so it's a perfect electrolyte.

Lower units usually contain dissimilar metals, stainless steel and aluminum. Immerse them in sea water and you begin their destruction.

If you look at the periodic chart you'll see which metal is the more noble. Stainless steel is mostly iron, so it's the more noble. The aluminum will be sacrificed by the the electrical current traveling between the two metals.

Type 304 stainless is not very noble and will begin to corrode internally. The iron seperating from the nickle and chromium. Type 316 is the prefered stainless alloy for boats. It's about three times as expensive as type 304.

Use of zincs (sacrificial anodes) give the electrolysis process something else to destroy. Is possible to over zinc.

Then there is the electrical bonding process that Tim Mattson mentions.

There are some other things going on as well. Stress corrosion, cavitation errosion and stray currents (from other sources) to name a few.

There are some books available on the subject. Marine Metals Manual and Corrosion Workbook.

Tim

[Tim_Mattson]

Forgot to mention the Air as the Catalyst.
Paint over SS boltheads and you`ll soon see the threads turn white as the SS starts to trade places with the Aluminum instead of being happy while exposed to air.
SS with Nickel in it is the best ,but SS is called "StainLESS" not "StainPROOF".Some is just better than others.
Air has "the proper number of Valence Electrons" while with the Alum,one is free to do the nasty business.
It`s all about chemistry,with a mix of voltage and "Primordial Soup".
Warmer water is also worsening the results,a Mexico based hull can become a worthless pile of powder in a season or two and Northwest waters seem to be rising in Temp each and every year.
Fluid Film spray is my best friend for corrrosion.....use liberally,especuially when new.
TimM

[Helmar]

More on Zinc's

I was not looking to become an expert on Zinc's but know that others have questions about them as well.

Me, I have been told to just go to the Honda shop and get a set of Honda Zincs to add to my Bearcat as she has Zero for zinc's.

Merc has there own blend as well.
Any reason the ones for the Hondas and Merc's would not work that anyone knows about

[Tim_Mattson]

Joe ,
I`d go smaller and see what happens.
You want it to be "Sacrificed" so if it goes away,then it worked.The goal is to last around 3 years before changing as it becomes more like chaulk than the pure Zinc/Magnesium that it started as.
If I owned a Bearcat ,then I`d pull a water jacket or T-stat cover and find a place to mount an internal Zinc like a Nissan or tohatsu uses......one little bolt is all it needs to be secured.
Japanese blocks seem to be more like Aircraft parts(Mitsubishi does them ALL.....) and seems like the Homelite is more like a US cast motor(not as pure).
I`d try the Merc or OMC "Teardrop" zincs on the cav plate/transom bracket,see what happens and add or leave as needed.
Day trips and non-moored boats really won`t need this if flushed well after use.
Always looking for more info if anyone else has more?
TM