which anodes for salt water

[agallant80]

Bravo3 in salt water. She lives on the trailer for now but will be slipped shortly.


Aluminum?
Zink?
Other?

 

[Slip Away]

Aluminum is best for salt. But if you have any zinc anodes on your BIII, they will all have to be changed to Aluminum.

 

[Scott Danforth]

mercruiser switched a while back to aluminum because people were complaining the zinc disappeared quickly. however zinc will be the best. Somewhere in the home office I have the Mercury

here is an article that I have bookmarked. http://my.boatus.com/consumer/BravoIII.asp

 

[dingbat]

Selecting an anode is a cost issue for the most part. Magnesium offers the most protection, but is consumed at an advanced rate in saltwater. Think Alka-seltzer.....

Zinc offer more protection, but at roughly a 30% higher rate of consumption than aluminum if all things where equal. Aluminum offers the least amount of protection of the three but has a slower rate of decay.

In the end, it comes down to protection verse consumption. A trailer boat with minimal exposure to stray currents from outside sources would do well with aluminum. If your a heavier user of shore power or keep the boat slipped in marina with a lot people using shore power, I'd go with the advanced protection of zinc and live with shorter life expectancy.

 

[dingbat]

Selecting an anode is a cost issue for the most part. Magnesium offers the most protection, but is consumed at an advanced rate in saltwater. Think Alka-seltzer.....

Zinc offer more protection, but at roughly a 30% higher rate of consumption than aluminum if all things where equal. Aluminum offers the least amount of protection of the three but has a slower rate of decay.

In the end, it comes down to protection verse consumption. A trailer boat with minimal exposure to stray currents from outside sources would do well with aluminum. If your a heavier user of shore power or keep the boat slipped in marina with a lot people using shore power, I'd go with the advanced protection of zinc and live with shorter life expectancy.

http://www.boatingmag.com/how-to/choosing-right-sacrificial-anode

 

[Thalasso]

The question is which is best for salt water. Zinc by far.
Aluminum is for brackish water. (salt/fresh mix).
What you should also be concerned with is the Mercathode. You should check the protection field after it is slipped for a week or so. You will need a silver chloride tester and digital multimeter to do this.
You will need to keep the battery charged because the Mercathode system will kill the battery

New boats just placed in service usually will produce a reading higher than normal. This is due to the drive unit being protected by a good finish and a new sacrificial zinc anodes. To obtain an accurate diagnosis, the test should be performed after the boat has been in service at least one or two weeks. This will give the paint a chance to "soak" and minor abrasions and scratches will have appeared, which will result in a more accurate reading.
Boats should be moored (without being operated) for at least 8 hours before performing tests. This is necessary to allow the MerCathode System and/or sacrificial zinc anodes to polarize the surrounding water. Be careful not to rock the boat excessively while boarding to perform test as this will alter the test reading.

880-1050 Milli-volts with Digital Meter
[h=2]Corrosion Reference Electrode Product Specifications[/h] www.boatzincs.com/corrosion-reference-electrode-specs.html

 

[Chris1956]

Crap, your outdrive is aluminum. So you want to protect it with the same metal? If you get a nick in your outdrive paint, then the anode will sacrifice at the same rate as the outdrive. Does that make any sense? My outdrive always seems to lose pain at the skeg. I need to protect that bare aluminum.

Get Zinc anodes for salt water. The more stainless steel (props, tabs) you have the more zinc anode protection you need. Anodes must be grounded to the boat's ground. If you put any on the PTT rods, for example, you may need ground wires, as those can be rubber mounted. Put anodes on the trim tabs as well.

 

[dingbat]

Crap, your outdrive is aluminum. So you want to protect it with the same metal?

That may be true if the out drive and anode where the same aluminum alloy, which they are not.

I suggest you read up on U.S. Military Specification MIL-A-24779(SH) Aluminum Alloy before making such assumptions. There is a reason why the US military now specs "aluminum" anodes for military vessels

Comparison between Anodes

Zinc Anodes​		Aluminum Anodes​
355 Ampere hours per pound		1225 Ampere hours per pound
This means a Zinc anode will give one amp for 355 hours for every pound of Zinc		This means an Aluminum anode will give one amp for 1225 hours for every pound of Aluminum
Take a typical Z3 (weight=4.68 kg) as seen on page 47 Total ampere hours 3656		Take a typical AZ3 (weight = 2.7 kg) as seen on page 47 Total ampere hours 6125
Assuming the anode performs at 0.5 amp		Assuming the anode performs at 0.5 amp
This anode will last for 7312 hours		This anode will last for 12250 hours
Which is 304 days		Which is 510 days
Which is 10 months		Which is 16.5 months

 

[dingbat]

...double post

 

[Chris1956]

ok, So zinc will last 300+ days and aluminum 500+ days. Does that take into account the outdrive, which may have a fair amount of copper in the alloy? The way I understand it, the copper content makes the aluminum more reactive.

So you are saying you plan to give up the extra protection of zinc (1 season/set), because aluminum lasts 2 seasons/set (in the northeast)? That makes no sense to me, sorry..... I would rather buy two sets of zinc anodes, and have the extra protection.

BTW - The US Military is very likely doing the analysis of another scenario, as Mil specs for vessels can easily be for exotic alloys. It's applicability is questionable to my issue.

 

[Thalasso]

It's either or. Really doesn't matter

• Zinc Alloy Anodes = Salt water only
  • Not recommended for use in fresh water
  • Alloy is manufactured to meet or exceed US Military Specification (MIL-A-18001K)
• Aluminum Alloy Anodes = Salt or Brackish water
  • Not recommended for use in fresh water
  • Proven to last longer than zinc due to increased capacity
  • Alloy is manufactured to meet or exceed US Military Specification (MIL-A-24779(SH))
• Magnesium Alloy Anodes = Fresh water only
  • Not recommended for use in salt or brackish water
  • The only alloy proven to protect your boat in fresh water

 

[Thalasso]

It's either or. Really doesn't matter
The best anodes are made from an "activated alloy" in which catalysts have been added to ensure that the anode gives 100% of itself
Myself i would rather use zinc because you can monitor it better (wear).
You do want the most active, not so much the one that will last the longest. They should be changed yearly anyhow

• Zinc Alloy Anodes = Salt water only
  • Not recommended for use in fresh water
  • Alloy is manufactured to meet or exceed US Military Specification (MIL-A-18001K)
• Aluminum Alloy Anodes = Salt or Brackish water
  • Not recommended for use in fresh water
  • Proven to last longer than zinc due to increased capacity
  • Alloy is manufactured to meet or exceed US Military Specification (MIL-A-24779(SH))
• Magnesium Alloy Anodes = Fresh water only
  • Not recommended for use in salt or brackish water
  • The only alloy proven to protect your boat in fresh water

 

[dingbat]

....

 

[agallant80]

I plan on replacing them as part of the yearly haul out. I will go with Zink.

Do I need zinks on the tabs if they are painted?

 

[Chris1956]

Yes, you need anodes on the trim tabs, because they are stainless, coated with copper paint. So you have dissimilar metals, in a salt bath. That is the definition of a battery.