Galvanic isolator vs isolation transformer

Both devices break the shore-side ground path that causes galvanic corrosion between boats on the same dock. A galvanic isolator uses back-to-back diodes to block low-voltage DC galvanic current (typically under 1.4V) while still passing AC fault current for safety. Cheaper (US$300-800), simpler, but does nothing against stray AC leakage and can fail closed (short) or open (no ground protection). Test annually with a galvanic isolator monitor. An isolation transformer physically breaks the shore ground, no galvanic connection at all. Handles stray AC, provides polarity correction, and often steps 240V split-phase to 120V for older boats. More expensive (US$2000-5000), heavier (60+ lb for 30A), consumes cabin space, but is the gold standard. Choice depends on marina, if you're on a dock with older wiring or lots of foreign-flag boats, transformer wins. Coastal cruising with modern marinas, isolator is enough. Never omit either on a metal-hulled boat.