Martyr CMR07 Rudder & Trim Tab Sacrificial Anode - 6-1/2" Diameter
- Anodes must be replaced when they are 70% eroded
- Martyr ( Canada Metal (Pacific) Limited ) only uses mil-spec mil-a-l800l alloy in all of their premium marine anodes
- This alloy helps the anode erode inward giving the anode a sandblasted appearance
- Canada Metal uses a special steel combination fastener that makes it possible to use their Ball drive, which is a hex driver with a universal ball tip (Ball-drive is Sold Separately)
What causes corrosion? Seawater is a good conductor and freshwater a bad conductor, so corrosion is worse in seawater. Generally, corrosion rates increase in proportion to the amount of oxygen in the water. However, cracks and crevices, which are areas starved of oxygen, become anodic and corrode also. Higher temperature increases corrosion rates - doubling for every 30 degrees C (55 degrees F). There are various types of microorganisms that can contribute to corrosion, either by removing protection or causing a corrosive environment.
Why do I need anodes? You need anodes on your engine because when two different metals are in contact, electrons will flow from the more negatively charged metal (anode) to the more positive metal (cathode). If you want to protect both types of metal from corrosion, you must add a third metal such as zinc, although magnesium and aluminum are also used. This active metal becomes the anode for both metals. The zinc or aluminum sacrifices itself to protect the other two metals, hence the term " sacrificial anode".
How to Choose the Correct Type of Anode
Throughout the world you may find many different water environments which may all require different solutions. The three main water types are salt, fresh and brackish. Martyr™ zinc and aluminum anodes protect very well in salt and brackish waters where magnesium anodes protect the best in fresh water. DO NOT MIX Zinc and Aluminum Anodes on the same vessel.
- 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, Fresh or Brackish water
- Not recommended, but can be used 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
- The only alloy proven to protect your boat in fresh water
- It is not recommended to use magnesium anodes in salt or brackish water .
- The result may be an accelerated corrosion rate, which may damage the metal parts of your boat and leave you with no anode protection in a short period of time.
- A Special Note on Magnesium Anodes for Fresh Water… Essentially, fresh water is a much less conductive environment than salt water, therefore magnesium anodes are your best choice as they are much more active (less noble) than zinc or aluminum anodes
- The result is increased efficiency thus superior protection for your underwater metal components