Sailboat operators must be cautious of what when passing under power lines and bridges?

Masthead clearance is critical for sailboat operators when passing under power lines and bridges because the height of the mast can vary significantly depending on the size and design of the sailboat. Ensuring adequate clearance is necessary to prevent collisions that could lead to damage to the boat, injury to occupants, or interference with power lines, which could also pose serious safety hazards.

Wind direction, engine power, and anchor depth, while all important considerations in boating, do not directly relate to the immediate concern of safely navigating under fixed structures. Wind direction affects sailing maneuvers, engine power is relevant for motorized movement, and anchor depth relates to where a boat can safely anchor without risk of grounding. However, none of these factors address the critical need to ensure that the mast can safely pass below the obstacle.