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.

Lunar age (d)

Age of the moon in days since new moon, 0 to 29.53.

Compute the spring/neap modulation factor from factor = abs(cos(2 * PI * lunarAgeDays / 29.53)); one means spring tides and zero means neap tides. 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]

Spring/neap factor

Spring/neap factor between zero (neap) and one (spring).

• 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.

• 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.

• Overfalls Risk Factor

  Estimate the severity of overfalls from the spring tidal range, maximum stream rate, and water depth.