Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Bridge air draft (m)

Vertical distance from the water to the lowest bridge span.

Height of tide (m)

Signed height of tide above chart datum; negative values indicate a falling tide below datum.

Vessel air draft (m)

Highest fixed point of the vessel above the waterline.

Compute the vertical margin under a chart-datum bridge clearance by subtracting both height of tide and vessel air draft. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Clearance (m)

Margin remaining between the masthead and the bridge; zero means a touch fit.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• UKC Calculator

  Compute the under keel clearance by subtracting the vessel draft from the depth of water.

• Drying Height Clearance

  Compute the water depth over a charted drying patch by subtracting its drying height from the height of tide; a negative result means the patch remains exposed.

• Berth Depth Check

  Check whether a marina berth holds enough water by adding the height of tide to the charted berth depth and comparing against the vessel draft.