Attaching sacrificial anodes to boats with ferrocement hulls

When attaching anodes to boats with ferrocement hulls, we recommend following the same instructions as for boats with GRP hulls. However, there are a number of additional instructions, which are as follows:

  • The hull steel reinforcement must be isolated as much as possible from any metal work that is connected to the cathodic protection system, e.g. shaft brackets, rudder bearings and glands, as well as the anode itself.
  • It is unlikely that the hull steel reinforcement can be completely isolated and it will put some demand on the sacrificial anode. Hence, it is important to select a large enough anode to provide sufficient protection for this accelerated activity.
  • When choosing this anode, we recommend that you refer to the instructions on boats with GRP hulls in salt water on our cathodic protection page, and select the anode which is a size larger than that suggested for conventional GRP-hulled vessels of the appropriate class.
  • Mild steel rudders, skegs and bilge keels should be protected using the ZD58 zinc disc anode.

When fitting anodes on a ferrocement hull, ensure that:

  • The anode fixing studs are isolated from the hull steel reinforcement by fitting a plastic insulating sleeve to the shank of the stud and by applying a generous amount of marine-grade sealant.
  • The anode-fixing stud collar is bedded in several layers of glass fibre and epoxy resin.
  • The anodes are fitted with rubberised foam backing pads.
  • The anodes are always fastened with serrated washers under the fixing nuts to ensure a good connection.
  • The anodes are bonded in accordance with the instructions for boats with GRP hulls.

Diagram for fitting instructions for ferrocrete vessels