Attaching sacrificial anodes to boats with wooden or GRP hulls

Key instructions

  • The anodes should be positioned on the outside of the hull, below the waterline.
  • There should be nothing obscuring the anodes from the parts to be protected.
  • The fixing studs must be located above the bilges.
  • The anodes must be located so as to ensure the minimum run of bonding cable to the parts to be protected.
  • There must be reasonable internal access to the fixing studs.
  • The anodes should not be positioned in front of or in line with echo-sounding transducers or log impellers.
  • The surface of the sacrificial anode should not be painted.

Fitting sacrificial anodes to the hull

  • If necessary, reinforce the inside of the hull where the anode is to be fitted.
  • Drill holes to take the fixing studs at the appropriate points.
  • On wooden-hulled boats, fixing studs should be sleeved or painted to insulate them from the surrounding timber. If you choose to sleeve the studs, use either a heat-shrink tube or ensure that the inside of the sleeve is packed with a suitable marine-grade sealant.
  • Before inserting and securing each fixing stud, apply a generous amount of marine-grade sealant to the shank and collar where the stud touches the hull to ensure a lasting seal.
  • 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 to protect the hull. The anode backing sheet should be replaced with every new anode.
  • When attaching anodes, always ensure that fan disc washers are fitted under the securing nuts. The washers help to assure the contact between the anode and the cathodic protection system. The fan disc washers and nuts should be replaced each time the anode is replaced.
  • Protect the fixing studs on assembly with paint or grease inside and outside the vessel.

Bonding the cathodic protection system

  • Use 4mm² or larger PVC-insulated multi-stranded copper cable.
  • Ensure that all connections are clean and tight.
  • The best way to bond the anode to the propeller shaft, gearbox or engine casing is by using an electro eliminator.
  • Insulated flexible couplings should be bridged by a short length of bonding cable or a copper strap to carry through the contact between anode and propeller.
  • Bronze and stainless steel rudders, rudder hangings and shaft brackets should also be bonded to the main anodes.
  • Trim tabs should be protected with separate anodes.
  • Steel rudders must be protected with separate anodes.
  • Do not fit the same anode to ferrous and non-ferrous metals.
  • Timber-hulled boats may be prone to electro-chemical decay and we recommend that owners contact Anode Outlet for specialist advice.