Use this sailing calculation for planning or education when the vessel, units, reference directions, environmental conditions, and assumptions are explicitly known.

Water depth (m)

Required number in m. Total depth of water beneath the vessel.

Vessel draft (m)

Required number in m. Draft of the vessel.

The cited overview of Sailing supplies background for the terminology and domain context used by this tool.^[1]

Compute the under keel clearance by subtracting the vessel draft from the depth of water. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Under keel clearance (m)

Returned number in m. Clearance between the keel and the seabed.

• Vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, and safety margins can make real conditions differ from a simplified result.
• Water depth must be at least 0.
• Vessel draft must be at least 0.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Cross-check current charts, tide and weather services, instrument data, vessel manuals, and applicable navigation rules, and retain a conservative alternative plan.

• Bridge Clearance Calculator

  Compute the vertical margin under a chart-datum bridge clearance by subtracting both height of tide and vessel air draft.

• 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.