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

Luff length (m)

Required number in m. Luff length of the spinnaker from tack to head.

Luff percentage (%)

Optional number in %. Fraction of the luff extended between the raised tack and the fixed full-hoist head; ninety five percent leaves five percent available as tack lift.

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

Estimate how high the spinnaker tack can be raised below a fixed full-hoist head position from the unused fraction of the luff length. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Tack height (cm)

Returned number in cm. Estimated tack lift above the full-luff tack position, rounded to centimeters.

• 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.
• Luff percentage must be at least 50.
• Luff percentage must be no greater than 100.
• 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.

• Spinnaker Pole Height

  Compute how high the outboard tip of a spinnaker pole sits above the mast attachment using pole length times the sine of the elevation angle.

• Post-Tack Acceleration Time

  Estimate how long a boat needs to recover full speed after a tack from the speed deficit and the acceleration rate.

• Anchor Circle Radius Calculator

  Estimate the maximum anchor-to-bow radius from water depth and rode scope. Add the vessel length when checking the full area swept by the stern.