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

Range difference (m)

Required number in m. Signed difference in tidal range between ports.

Interpolation proportion

Required number. Proportion interpolated from the correction table.

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

Compute the secondary port height correction from the signed difference in tidal range and an interpolation proportion taken from almanac tables. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Correction (m)

Returned number in m. Signed height correction for the secondary port.

• 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.
• Interpolation proportion must be at least 0.
• Interpolation proportion must be no greater than 1.
• 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.

• Current Correction Angle Calculator

  Compute the signed crab angle needed to oppose a current's cross-track component. Routes whose cross-current exceeds boat speed cannot be held.

• Horizon Range Calculator

  Compute the distance to the visible horizon in nautical miles as one point one seven times the square root of the observer height in feet.

• Tidal Curve Height

  Interpolate a falling tide from high water to low water with a cosine curve over the specified high-to-low interval.