Teardrop Zinc Hull Anode | Martyr CMT20 Traditional zinc Martyr anode protects boat's hull from corrosion in salt water. CMT20 sacrificial anode Zinc anode is for use in salt water Martyr anodes are made of a high purity specialized alloy based on the US Mil Spec Bolt-on style anode is designed to mount to hull 3.4 in. length 1.8 in. height .6 in. thickness