Sailing Calculators
Free sailing calculators for course plotting, tidal heights, hull speed, anchor scope, passage time planning, and racing handicaps.
Navigation, tides, boat performance and rig numbers. 13 calculators for passage planning and for understanding what a hull will actually do.
Hull speed is the classic displacement limit, 1.34 times the square root of waterline length in feet, giving knots. A 30 foot waterline works out around 7.3 knots. Worth knowing that it is a soft ceiling rather than a wall: the resistance curve climbs very steeply there, so pushing past it costs power out of all proportion, which is why a displacement hull with twice the engine gains barely a knot. Long waterline is the only real answer, and it is why waterline length rather than overall length predicts passage times.
Apparent wind explains the result that surprises new sailors: a boat sailing upwind feels more wind than exists, because boat speed adds vectorially to true wind. Bear away downwind and the apparent wind drops, sometimes dramatically, which is why a run that feels gentle can be carrying far more true breeze than the crew realise until they turn back.
Capsize screening is a rough offshore suitability indicator from beam and displacement, and under 2 is the usual threshold. It is a screen, not a verdict.
Sailboat Capsize Screen Factor Calculator
Calculate the offshore capsize screening factor for any monohull sailboat from beam and displacement. Under 2.0 is considered offshore-capable by ORC.
Sail Trim by Point of Sail Calculator
Get sail trim angle and traveler position for any point of sail. Reference table for close-hauled, beam reach, broad reach, and run with twist guidance.
Sailing Velocity Made Good (VMG) Calculator
Calculate sailing VMG to windward or leeward by boat speed and wind angle. Find optimal pointing angle and tacking strategy for upwind and downwind legs.
Apparent Wind Calculator
Calculate apparent wind speed and angle from true wind speed, true wind angle, and boat speed. Essential for sail trim and racing tactics.
Course to Steer Calculator
Calculate the compass heading to steer to counteract tidal current and leeway. Find the actual course made good and estimated speed over ground.
Hull Speed Calculator
Calculate the theoretical hull speed of a displacement boat from waterline length. See the Froude number threshold and power required to exceed hull speed.
Mast Rake Calculator
Calculate mast rake angle from mast height and horizontal offset. Helps optimize helm balance by adjusting rake forward or aft on dinghies and keelboats.
Sail Area Calculator
Calculate total sail area for a sloop rig (mainsail + jib). Compute sail area-to-displacement ratio to assess boat performance.
Sailboat Heeling Angle Calculator
Estimate a sailboat heeling angle from wind pressure and righting moment. Understand the stability trade-off for different sail configurations.
Sailing Dead Reckoning Calculator
Dead reckoning at sea: estimate a new lat/lon from heading, speed, and time, or solve distance, speed, and time for passage planning in knots.
Sailing Handicap Calculator (Portsmouth Yardstick)
Calculate corrected time for handicap sailing races using the Portsmouth Yardstick (PY) system. Compare two boats to find the race winner on corrected time.
Tidal Current Speed Calculator
Estimate tidal current speed at any point in the tidal cycle using the 50/90 rule. Enter the maximum current speed and the hours since slack water.
Tidal Height Calculator
Estimate the height of tide at any time between high and low water using the 1/12 rule. Find out if there is enough depth to enter a harbour or anchorage.