The MGDuff AD78B is popular hull anode for brackish waters. Hole centres distance is 8". People tend to use zinc because its cheaper but aluminium anodes are a lot lighter and can used in brackish waters.
Nominal Weigth 1.7kg
Bolt-on, Holes Centres 200mm
Length 305mm Width 76mm Depth 36mm
Material: Aluminium for brackish waters
Stud Size: 10mm
Number of Fixing Holes: 2
Fixing Hole Details: 19mm x 11mm holes at 200mm centres