Anodes

[l008com]

I like to have an image on my threads to be extra clear what I'm talking about. But I don't have a great picture of what this thread is about. So instead, here is a picture of a trashbag I caught in the Mystic River that stalled my motor

On to my question. My anode trim tab is looking a little beat. Easy enough to replace. It's a 90hp 3cyl mercury outboard. From what I've seen online, all outboard mercuries take the same trim anode, is that true? If so, that should be easy enough.

Now come to find out, there is supposed to be a second anode on the of the motor mount right up against the transom. My boat doesn't have this. And it never has. Are those anodes good to have?

I use my boat in salt water, but I don't store it in water, I trailer it. And I launch a good 10 minutes up the fresh water side of the locks, so everything gets a thorough fresh water rinsing before it gets pulled. Is that second anode worth getting? Or is it not really useful with the way I use my boat?

And also, aluminum or zinc? What's the difference?

Oh and here we go, I just found a more relevant picture of the area of my boat in question:

 

[1960 Starflite]

Re: Anodes

I would suggest using Zinc. My lower unit had aluminum anodes on it and didn't work at all. The lower unit was corroding away without any effect on the anode. I changed to zinc and now after one season the lower unit looks fine and the anode is wasting away. My boat sits in the water all summer.

As to the anode nuts on the transom mount, mine look like new, SO thay aren't doing their job.

 

[Chris1956]

Re: Anodes

If you trailer your boat, anodes are not necessary. However, since the one above the prop helps with steering torque, I recommend you keep that one in good shape. Merc actually has three or four different anodes that fit that area. One is standard, one has a recessed fin and is used for high performance (raked) props. The third is a disc of zinc, without a fin, and there are also anodes with smaller than normal fins.

 

[SteveMcD]

Re: Anodes

Once the metal corrodes off your drive, it's gone. You can never get it back. Anodes are dirt cheap. If you are trailering and rinsing, they should last for years. One on the transom shield too may be a good idea. My Volvo drive has one. The plastic bushings, grease, etc can't be helping the connection any. Maybe that's why it's there. I would be surprised to hear yours never had one. Maybe get a three or four inch trim tab anode and bolt it on.The difference between them is metal activity. Magnesium is at the top, aluminum in the middle, and zinc at the bottom. Zinc is for salt water. My zincs were 60% gone after 6 months. After 6 months in fresh water, they were intact and there were corrosion spots on my drive. I was told I need magnesium anodes for fresh water. My guess is magnesium anodes will have a much shorter lifespan in salt water