Fitting and Bonding Anodes

Protecting a boat’s metal components from corrosion is one of the most important aspects of proper maintenance, especially in saltwater environments. Without adequate protection, underwater metals such as propellers, shafts, rudders, and trim tabs can quickly deteriorate due to galvanic corrosion.

The most effective way to combat this is by fitting sacrificial anodes, often made from zinc, aluminum, or magnesium. These anodes act as a “sacrificial metal,” corroding in place of the more valuable parts of your boat. However, simply attaching anodes isn’t enough. For them to work properly, they must be correctly bonded to the boat’s electrical and metal systems, ensuring a continuous, low-resistance path for the protective current to flow.

When fitting anodes to wooden or GRP hulled vessels, remember: 

• The anode should be positioned on the outside of the hull below the waterline.
• The anodes can “see” the parts to be protected.
• The fixing studs are located above the bilges. 
• The anode location ensures the minimum run of bonding cable to the parts to be protected. 
• There must be reasonable internal access to the studs. 
• The anode should not be positioned forward of, or in-line with Echo Sounding Transducers or log impellers. 
• It’s important to note that magnesium anodes should never be fitted to wooden hulled vessels as they can damage the timber.

Hull Anode Installation

1. Stiffen the inside of the hull where the anode is to be fitted if necessary.

2. Drill holes to take the fixing studs at the appropriate centres.

3. On wooden hulled vessels, studs should be sleeved or painted to insulate them from the surrounding timber. When sleeving the stud either use a heat shrink tube or ensure that the inside of the sleeve is packed with marine grade sealant.

4. Before inserting and securing each stud assembly, apply a generous amount of marine grade sealant to the shank and collar where the stud touches the hull to ensure a good seal.

5. Whenever an anode is fitted to a GRP or wooden hull, an anode backing sheet must be used to control the wastage of the anode and protect the hull. The anode backing sheet should be replaced each time the anode is replaced.

6. Always ensure that the anodes are fitted with MGDUFF Fan Disc Washers under the securing nuts which will help to assure the contact between anode and and cathodic protection system. The fan disc washers and nuts should be replaced each time the anode is replaced.

7. Protect the anode fixing studs on assembly with paint or grease inside the and outside the vessel.

Bonding the Cathodic Protection System

1. The correct bonding of the cathodic protection system is imperative.

2. Use 4mm² PVC insulated Multi-Stranded Copper Cable or larger.

3. Make sure all connections are clean and tight.

4. The best way to bond the anode to the shaft is by using an MGDUFF Electro Eliminator as well as bonding the anode to the gear box or Engine casing.

5. Insulated Flexible Couplings should be bridged by using an earthing connector between the anode shaft and propeller.

6. Bronze and Stainless Steel Rudders, Rudder Hangings and Shaft Brackets should also be bonded to the main anodes.

7. Trim Tabs should be protected with separate anodes.

8. Do not bond the same anode to ferrous and non-ferrous metals.

9. Steel Rudders must be protected with separate anodes.