Which condition is essential for ensuring safety during lightering operations in the harbor?

The condition that ensures safety during lightering operations in the harbor primarily hinges on sustained winds below 40 knots. Lightering operations, which involve transferring cargo between vessels to accommodate port limits or channel depths, can pose significant risks, particularly due to the forces exerted by wind on the lightering vessels. Strong winds can affect maneuverability, stability, and control, increasing the chances of accidents or mishaps during the transfer of cargo.

When winds exceed safe thresholds, the operations may become hazardous, leading to potential collisions, capsizing, or loss of cargo. Therefore, maintaining sustained winds below 40 knots is essential for managing these risks effectively.

Calm waters and clear weather are certainly beneficial conditions that improve the overall safety and success of lightering operations, but they do not specifically address the direct impact of wind on operational safety. Full crew availability is important for operational efficiency and response in case of emergencies, but in the context of ensuring safety from environmental factors, it's not as critical as controlling wind conditions. Thus, sustained winds below 40 knots stand out as the pivotal condition for safety during lightering.