Unexpected underwater metal loss deserves attention, but adding more anodes or changing a bonding connection before understanding the problem can obscure the cause. Galvanic corrosion, stray-current corrosion, grounding, bonding, and cathodic protection describe different mechanisms and functions.
Knowing those distinctions helps you preserve useful observations and ask for the right assessment. Start with your new yacht handover documents, current electrical drawings, service history, and anode records. The boat’s actual arrangement matters more than a familiar wire color or another yacht’s installation.
Distinguish Galvanic and Stray-Current Corrosion
Galvanic corrosion can occur when different metals are electrically connected in an electrolyte such as seawater. The less noble metal in that relationship can lose material. Which metals are present, how they connect, and the surrounding water influence the relationship.
Stray-current corrosion involves current taking an unintended path through water and metal. Its source may be aboard, at the dock, or elsewhere in the surrounding electrical environment. ABYC corrosion education treats these corrosion types, shore-power systems, cathodic protection, and corrosion surveys as distinct professional subjects.
Appearance alone cannot establish the cause. Pitting, deposits, coating damage, and anode consumption provide observations for an investigation, rather than a reliable diagnosis. Avoid assigning a universal rate or time to failure: different arrangements and conditions can produce different outcomes.
Separate Bonding, Grounding, and Cathodic Protection
These functions can interact within a designed installation, but their names are not interchangeable.
| Term | Main purpose | Useful owner question |
|---|---|---|
| Cathodic bonding | Electrically interconnects protected metals sharing water with the cathodic-protection source | Which components are included in this boat’s documented arrangement? |
| Electrical grounding | Serves electrical safety or system-reference functions, depending on the circuit | Do the current drawings reflect the installed system and later work? |
| Cathodic protection | Reduces corrosion of the metals included in the protective arrangement | What protection source and specifications apply to those components? |
ABYC cathodic bonding guidance explains that cathodic protection is an if-installed requirement under its standards. That distinction does not determine whether a particular yacht needs a particular arrangement. The installed design and applicable requirements need professional interpretation.
Do not add, remove, reconnect, or bypass conductors to resolve a corrosion concern. Wire color and visual proximity cannot establish how a connection should function. Keep grounding and corrosion questions together in the professional brief without treating one as a substitute for the other.
Treat Anodes as Parts of the Designed System
A sacrificial anode supplies protection within a cathodic-protection arrangement. Its material, size, attachment, and location must suit the equipment, protected metals, water environment, and design. More anodes do not automatically establish correct protection.
Record each documented anode’s part or material specification, location, installation date, and condition at inspection. Keep invoices and photographs so a professional can compare changes over time. Ask whether a move between fresh, brackish, and salt water changes the approved specification for the actual equipment.
Visible consumption does not tell the whole story. Unexpectedly rapid loss, loose attachment, or an unusual lack of wear merits assessment, but a percentage by itself cannot establish the cause or prescribe a different alloy. Avoid copying another yacht’s replacement interval or protection readings.
Understand the Shore-Power Connection
A shore connection can link the boat to a wider marina electrical environment. The boat’s grounding design and any isolation equipment determine how that connection relates to underwater metals.
A galvanic isolator and an isolation transformer use different principles. An isolator can interrupt certain low-voltage galvanic paths while retaining its specified safety function. A transformer transfers power magnetically and provides separation according to its installation design. Neither name alone proves the protection or condition of the equipment aboard your boat.
Record whether either device is installed, its manufacturer and model, the matching manual, and recent shore-power or electrical work. Leave testing and diagnosis to qualified support. Never disconnect a safety-ground conductor or bypass equipment to chase anode wear.
Your shore power, inverters, and battery routine addresses ordinary energy management. Heat, damaged connections, repeated protective-device operation, odor, smoke, or a shock concern needs prompt qualified or emergency assistance appropriate to the conditions.
Build a Useful Corrosion Survey Brief
When planning a cruising-yacht haul-out, coordinate any corrosion assessment before arrival so the professional can define the access and observations required. Some assessment may involve the boat afloat and some may need the hull visible; the surveyor should decide the appropriate scope.
Gather:
- Dated photographs of affected metal and anodes, taken without disturbing the evidence.
- Locations, water conditions, and marina or berth changes.
- Electrical modifications, outages, and recent service events.
- Prior corrosion surveys, anode invoices, and haul-out findings.
- Current drawings and manuals, with missing or conflicting information marked clearly.
Ask the professional when photographs or other observations should be made relative to washing and service. Keep direct observations separate from theories about a neighboring boat or a particular circuit.
Arrange assessment for unexplained or accelerated metal loss, damaged shore-power equipment, recurring electrical concerns, or a protection arrangement that cannot be reconciled with the records. An active electrical hazard calls for the vessel and marina emergency procedures rather than continued inspection.
If you need available builder records or want to discuss access to the documented systems aboard your yacht, contact us. Clear records and accurate terminology help the professional investigate the actual boat without beginning from a guessed repair.