USCG Warns Shipowners to Verify Air Draft, Avoid Bridge Strike
The U.S. Coast Guard (USCG) has issued a Marine Safety Alert warning vessel owners, operators and crews to verify their ships' maximum air draft before transiting beneath bridges and other overhead obstructions, following an incident in which an unaccounted-for antenna struck a bridge.
In Safety Alert 17-26, issued November 10, 2026, the Coast Guard detailed its investigation of a deep-draft vessel that contacted a bridge despite voyage-planning calculations indicating sufficient vertical clearance.
Investigators determined that the vessel's reported air draft was based on outdated plans that did not reflect its current configuration. Multiple versions of the ship's plans were maintained on board, and the documents used to calculate air draft failed to account for an installed MF/HF tiltable antenna extending above the vessel's reported highest point.
Because the antenna was omitted from the calculation, the crew did not recognize the need to lower it before passing beneath the bridge. The vessel's pilot subsequently received an understated air-draft figure, creating a false margin of safety during transit planning.
The incident highlights the risks associated with vessel modifications and equipment installations that alter a ship's vertical profile without corresponding updates to technical documentation and operating procedures.
The Coast Guard recommends that shipowners and operators incorporate air-draft verification into their safety management systems, maintain current vessel-specific drawings, and clearly identify or remove superseded documentation.
Operators should also establish procedures for configuring movable equipment before overhead-clearance transits and require positive confirmation that antennas and other adjustable structures are properly lowered or secured.
The alert was developed by USCG Sector Los Angeles–Long Beach and distributed by the Coast Guard's Office of Investigations and Casualty Analysis.
