Sacrificial Anode Service Life
How long a boat's zinc, aluminum, or magnesium anode lasts, by Faraday's law: 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.
Formula and source
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.
Audience
This tile is built for mechanics and the adjacent professions in the Mechanic - Auto, Marine, Aviation group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.