Zinc Anode Replacement Kamsar

Zinc has long been the standard anode material for ships, and zinc anode replacement is one of the most frequent underwater jobs. However, the right anode depends on the water the ship spends time in. Kamsar lies in an estuary where salinity varies, and the choice between zinc and aluminium anodes needs thought. This page gives the technical background and shows how we handle replacement.

Zinc Compared With Aluminium

Zinc anodes are reliable in seawater and brackish water and are widely used on hulls and in sea chests. Their electrochemical capacity is around 780 ampere-hours per kilogram. Aluminium alloy anodes have a much higher capacity, often over 2,500 ampere-hours per kilogram, so they last longer for the same weight, but they must be correctly alloyed to work in lower salinity. Magnesium anodes are used in fresh water. For ships moving between estuary and open sea, the anode specification should match the water in which the ship spends most of her time.

Brackish Water Considerations

In the Rio Nunez estuary, salinity changes with tide and season. At low salinity, some aluminium alloys passivate and lose effectiveness, while zinc generally continues to work. Many ships therefore use zinc or a specially activated aluminium alloy. We advise on the right material using the ship's anode plan and trading pattern, and we supply anodes with test certificates showing composition.

Wastage Limits

• New anode: 100 per cent of design mass.
• Typical replacement point: around 50 per cent of mass consumed, or when the remaining life will not reach the next dry-docking.
• Detached or cracked anodes: replace at once, regardless of mass.
• Anodes coated with paint or fouling: clean and check, as coating blocks current output.

How We Replace Zinc Anodes

The Diver cleans the mounting area, removes the old anode by unbolting or cutting the strap, and prepares the surface. A new zinc anode of the same size and type is fitted, and welds or bolts are checked for sound electrical contact. The anode face must be bare metal and must not be painted. Photographs show each anode before and after.

Special Positions

Anodes near the propeller, on the rudder and in sea chests protect fittings with different metals, which corrode quickly in contact with steel. Rudder anodes and propeller boss anodes often need replacement more frequently, because the high-speed flow consumes them faster. We pay special attention to these positions and note their condition in the report.

Records for Class and Owners

The report lists the anode type, number, position and mass replaced. It also records certificates of composition. This helps the owner to calculate consumption rate, so that the next replacement can be planned accurately. Class surveyors can also review the record when assessing the hull's protection at a UWILD.

Order Zinc Anodes

Send us your anode plan and ship details, and we will confirm material, supply and replacement time.

Checking Anode Certificates and Specification

Anodes should meet a recognised specification, such as the one used by many navies and class societies for zinc alloy anodes. Each batch should have a certificate of composition showing low iron content and correct alloy. Poor-quality zinc can passivate and lose effectiveness. We check certificates on delivery, record batch numbers and keep them with the report. This simple check protects the ship from fitting anodes that do not work.

Storage and Handling of Anodes

Anodes should be stored dry, away from oil and paint, and handled with care. Painted or oily anodes do not work. We check the surfaces before fitting and clean them if needed. Mounting hardware, such as bolts and washers, should be of suitable material and tightened to the correct torque. Good handling avoids waste and ensures the anodes do what they are meant to do.

Frequently Asked Questions (FAQ)

Q1. What is the electrochemical capacity of zinc anodes?

About 780 ampere-hours per kilogram.

Q2. Which anodes suit low salinity water?

Zinc works well in brackish water, while aluminium alloys must be specially activated for low salinity.

Q3. At what wastage should an anode be replaced?

Typically when around 50 per cent of its mass is consumed or if it will not last until the next dry-docking.

Q4. Why must anodes not be painted?

Paint blocks the current, so the anode would not protect the hull.

Q5. Which anodes wear fastest?

Those on the rudder and around the propeller, where water flow is high.