Mixing anodes

[barling]

My 2014 Ranger 31S now has a mix of anodes. This was not my intent. However, presently the thruster and the Prop nut have new zinc anodes. The local Volvo certified person says Volvo only authorizes engine zinc anodes. I replaced new magnesium anodes on the rudder and the trim tabs where there were good zinc. The 12 by 6 inch plate on the stern of the boat is still good zinc anodes. The boat has previously been in salt, but it will now be only in Lake Michigan. It was my hope to splash the boat this coming Friday, but I do not want to damage the boat by this mix of anodes. The boat will be in Lake Michigan this year for only 9 weeks before it is pulled. I could easily reinstall the good zinc on the rudder and the trim tabs.
What do you advise?
Thank you. John

 

[ohioan55]

If the boat is in fresh water, then magnesium anodes are what you should be using. Zinc, I don't use any more as I prefer aluminum for both brackish and salt water. There is a good amount of research on this topic.

 

[BB marine]

The engine anodes will be fine if zinc. That is what Volvo uses and really doesn't mix with the underwater hardware. Using mixed anode material is not a good practice. Probably will not damage the equipment but it is not going to help protect it either.

 

[Brian98133]

The trim tabs on my '20 R23 didn't have any anodes... so I was going to put AL discs on them. Certainly not an expert in this field, so glad I saw this thread!

Anyone know what mat'l the factory uses, and/or what Yamaha uses? Would it be a good idea to install anodes on the tabs? I was surprised they didn't come that way from the factory. My last 2 boats that had trim tabs had anodes, so I assumed it was standard...

Thanks in advance!

 

[BB marine]

Bennett does not require anodes on trim tabs in fresh water so there are not provisions for a anode from Bennett. Bennett does suggest that anodes be installed if the boat is left in the water, salt or brackish water. It is up to the boat manufacture to follow through with this recommendation. It is a production cost savings to not install anodes. Most reputable dealerships will install the anodes during the rigging process if they are aware that the boat owner will be storing the boat in the water and it is salt or brackish. With trailerable boats this is 50/50.

I would recommend installing anodes to the trim tabs regardless of use fresh water, brackish, salt or trailer. I do not recommend zinc anodes for trailerable boats. I do not recommend using zinc anodes for protecting outboards. I do not recommend using zinc anodes in fresh water. The aluminum will give better protection. The manufacture of Ranger Tugs and Cutwater does recommend for some reason. The reason zincs are not the best choice for trailerable boats or fresh water boats is the zinc will form an oxidation coating (calcareous coating),when introduced to air after being in the water or in fresh water. Once this oxidation has formed it will not be an active anode. The reason that zincs are not recommended for outboards is the zinc is slightly more noble than the aluminum alloy and doesn't provide as much protection. Pound to pound aluminum has a much higher longevity.The relative energy capacity of zinc is 368 amp hours per pound with a voltage of negative 1,050 millivolts.The relative energy capacity of aluminum is 1,108 amp hours per pound (significantly more than zinc), with a voltage of negative 1,100 millivolts. If you opt for aluminum anodes, be sure that the change is universal.

This is my opinion. I am not an expert on this subject. I just have opinions based on the subject. Zincs were fazed out in the late 80's early 90's by some outboard manufactures. Mercury marine voided the corrosion protection warranty if Zinc anodes were used on their products. There are many articles available to research the best anode protection for the type of equipment you have and the water you run it in.

 

[NorthernFocus]

...I do not want to damage the boat by this mix of anodes...

While the discussion of zincs can get very confusing with seemingly contrary opinions on what's best, having mixed anodes will not damage your boat. The level of protections may be more or less effective based on the choice of anodes but the anodes will not be a cause of corrosion/electrolisis to other parts of the boat. The one exception to that may be for outboards as Brian pointed out. But for a boat with inboard propulsion as long as you have the manufacturer's specified anodes in the engine you'll be fine. The stainless and bronze hardware that is below the water line is more noble than any of the anode materials so will not be damaged regardless of which anodes are used.

That said, with mixed anodes you may experience shorter anode service life as they will "eat" one another with the least noble of the mix suffering. However in fresh water it's not likely to make a significant difference.

 

[ohioan55]

I agree with not mixing the anodes. I won't get into the stray current thing.