I boat strictly in fresh water and for the last nine years have left the boat in the water approximately six months each year. My trim tab anodes (same type as used on rudders) are likely original 1997 zincs and they are now about 30% original size. I wonder if these zinc anodes are serving any purpose. I also wonder if replacing these zincs with magnesium anodes would help anything (such as possibly further protecting my Volvo Penta DPS outdrive). I don't think the trim tabs are electrically bonded to anything (1997 Larson 270 Cabrio). Thanks!
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Bennett Trim Tab Anodes
- Thread starter Riverratt
- Start date
Anodes only offer protection to ferrous metals that the anode is directly in contact with by physical contact or by a use of a jumper wire connector. The anode on your trim tab only protects the trim tab, it offers nothing in the way of protection to your out drive, unless a jumper wire or other connection exist. The fact that 70% of the anode is consumed indicates to me that the anode was working at one time. In its present state I doubt it is offering much protection and the anode should be renewed. If you use the boat in fresh water exclusively magnesium is the way to go.
As L.Keith stated, the reason the anode is not being consumed is that if you are using zinc in freshwater, you have the wrong anode. Zinc is for saltwater. In fresh water you need to use a magnesium anode. There are three types of sacrificial anodes. Zinc for saltwater, magnesium for freshwater, and aluminum/zinc for brackish water. Using the wrong anode will not provide sufficient protection.
- Joined
- Nov 24, 2001
- RO Number
- 6821
- Messages
- 42
Whichever Zinc you use make sure it is bonded to the metal not a paint layer first.
wayne.alexander
Member
- Joined
- Sep 7, 2004
- RO Number
- 15185
- Messages
- 23
For L. Keith: Zinc anodes will protect both ferrous AND non-ferrous metals also in salt and brackish waters.
In freshwater, zinc anodes have enough potential to "partially" protect. That's the bad news. The good news is corrosion rates are much lower in freshwater and since partial protection is occuring, corrosion is at a minimum
Aluminum anodes (in freshwater) have a tendency to film over which can result in passivation. These anodes are best used in salt and the upper levels of brackish. They may require maintenance (cleaning) in some cases to keep from filming over
Magnesium works well in freshwater, but also is used in brackish and saltwater. Because of the higher potential of these anodes, over-voltage (hydrogen release) can a more serious issue if not done right
In freshwater, zinc anodes have enough potential to "partially" protect. That's the bad news. The good news is corrosion rates are much lower in freshwater and since partial protection is occuring, corrosion is at a minimum
Aluminum anodes (in freshwater) have a tendency to film over which can result in passivation. These anodes are best used in salt and the upper levels of brackish. They may require maintenance (cleaning) in some cases to keep from filming over
Magnesium works well in freshwater, but also is used in brackish and saltwater. Because of the higher potential of these anodes, over-voltage (hydrogen release) can a more serious issue if not done right