Tides are the periodic rise and fall of sea level caused primarily by the gravitational pull of the moon and the sun. In most coastal regions the water level oscillates between a high tide and a low tide, creating a tidal range that can be several metres in magnitude.
Bridges spanning navigable waterways are designed with a nominal clearance measured from a fixed datum, usually chart datum (the lowest astronomical tide). The actual clearance available to a vessel at any moment depends on the current tide height and any additional safety margin required for wave action or vessel motion.
By combining the bridge’s nominal clearance with the observed tide level, engineers and mariners can quickly determine whether a vessel can safely pass beneath the structure. This simple calculation is essential for route planning, especially in ports with tight vertical constraints.
What is overhead clearance in maritime navigation?
How does tidal range affect bridge clearance?
What is chart datum in maritime navigation?
How do I calculate the actual clearance available to a vessel at any moment?
Why is it important to consider tides when designing bridges over waterways?
Can the overhead clearance calculator account for storm surges?
Results are for informational purposes only and do not constitute professional advice.