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

Low water (m)

Required number in m. Water level at low water.

High water (m)

Required number in m. Water level at high water.

Hours into interval (h)

Required number in h. Hours elapsed since high water.

Interval (h)

Required number in h. Length of the tidal interval.

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

Interpolate a falling tide from high water to low water with a cosine curve over the specified high-to-low interval. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Height (m)

Returned number in m. Interpolated tide height.

• 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.
• Hours into interval 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.

• Tide Height Cosine Curve

  Interpolate tide height on a cosine curve from heightM = lowWaterMeters + (highWaterMeters - lowWaterMeters) * (cos(PI * hoursFromHigh / 6) + 1) / 2.

• 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.

• Corrected Depth Calculator

  Add the height of tide to the charted depth sounding to obtain the actual depth of water.