A properly installed Zinc anode protects metal components
Corrosion is a destructive force. When certain metals come in contact with water, they can begin to degrade quickly. But in the case of storage tanks, steel water or fuel pipelines, and boats, contact with both fresh and saltwater is necessary.
Cathodic protection using sacrificial anodes can increase the life of metal parts. Sacrificial anode systems don’t need any external power sources and are easy to install and monitor. However, it is important to evaluate the amount of protection required to ensure the entire system functions properly.
The amount of current needed for a sacrificial anode to work depends on which metal or alloy the anode is made from and its size and shape. An experienced anode manufacturer, like Brooklyn, New York-based Belmont Metals, will be able to ensure its product line conforms to established standards for anodes. Belmont Metals has been manufacturing cathodic anodes made from Zinc and Zinc alloys for more than 50 years and recommends them for marine use, storage tanks, and steel water and fuel pipelines.
Once an anode’s output has been verified, the requirements for a specific application can be calculated. For a ship, first calculate separately the total immersed area of the steel hull as well as the total area of cathodic metals. Once you have that number, plan for one AZI Type 6-23 (6 inch by 12 inch, 23 pound) or Type ZHS-23-inch Zinc anode for each 100 square feet of immersed steel hull area and one for each 5 square feet of cathodic metal—propellers, shafts, bearings and rudders.
Place the majority of the anodes on the stern half of the ship near the propeller. Often, the anodes on a ship can be installed end-to-end parallel to and below the bilge keel along each side of the vessel, which minimizes parasitic drag. Anode locations on barges, buoys, and pontoons are not critical, but in general, the anodes should be evenly spaced for good current distribution.
When installing a Zinc anode, remove the galvanizing from the straps and weld all four straps to the hull. The anode can be bent to conform to the contour of the mounting surface if the bending radius is no smaller than 15 inches and the anode is heated to a temperature of between 200 degrees and 400 degrees Fahrenheit. Do not paint or coat the Zinc anodes; however, the other metals can be painted to help extend their lifespan as well as the lifespan of the Zinc anode.
Using these calculations, a tugboat that has an immersed hull area of 1,000 square feet and a 4-foot-diameter, three-bladed bronze propeller will need a minimum of 17 anodes—10 Zinc anodes for its hull and seven Zinc anodes to protect the propeller’s 32 square feet (one anode per each 5 square feet of bronze). If fewer than 17 are installed, the hull and propeller may be inadequately protected. If more than 17 are installed, the total life of the anodes may increase. Normal lifespan for these types of Zinc anodes in seawater is approximately one to two years.