Sacrificial Anode Service Life

life = anode mass x electrochemical capacity x utilization / (protective current x 8760 h). A 5 lb zinc (354 A-h/lb) at 0.85 utilization drawing 0.15 A lasts about 1.1 years -- the annual haul-out replacement. Aluminum (Al-Zn-In, ~1150 A-h/lb) of equal mass lasts far longer per amp and works in brackish water where zinc passivates, which is why it has largely replaced zinc. The protective current depends on wetted area, coating, and water; measure it with a reference electrode. Replace at about half consumed. A planning estimate; ABYC E-2 and a corrosion survey govern.

life_hours = anode_mass_lb x capacity_Ah_per_lb x utilization / current_A; life_years = life_hours / 8760. Capacity: zinc 354, aluminum (Al-Zn-In) 1150, magnesium 500 A-h/lb.

Sacrificial-anode life by Faraday's law of electrolysis (ABYC E-2 cathodic protection; DNV-RP-B401 anode capacities), by name; a corrosion survey and reference-cell reading govern.

Faraday's law is public; the electrochemical capacities are published anode-material properties. The protective current comes from a reference-electrode measurement of the boat.

Estimate. AHJ and licensed professional govern.

Field names used by the API: anode_material, anode_mass_lb, current_draw_a, utilization_factor, life_years, consumption_lb_per_year

• Electrochemical capacity zinc ~354, aluminum (Al-Zn-In) ~1150, magnesium ~500 A-h/lbDNV-RP-B401 / ABYC E-2
• Utilization factor ~0.85 for a slender standoff anode (the anode is ineffective before fully consumed)DNV-RP-B401