Sailing Tools
Browse all available sailing tools.
Available tools
- Air Draft With Heel Estimate effective air draft while heeled using a simplified rotation about the lower rail. Actual clearance also depends on hull geometry, trim, waves, and the heel pivot.
- AIS Range Estimate Estimate the range at which an automatic identification system target is received as one point one seven times the sum of the square roots of the own and target antenna heights in feet.
- 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.
- Anchor Rode Length Calculator Compute the anchor rode length needed from water depth, freeboard, and scope ratio.
- Anchor Scope Ratio Calculator Compute the scope ratio from the deployed rode length and the total height to the bow chock.
- Anderson Turn Course Calculate the return course reached by an Anderson turn, which rotates the heading two hundred forty degrees toward the chosen turn direction to bring the vessel back along its original track.
- Apparent Temperature Calculator Compute the simplified apparent temperature from air temperature, humidity-derived vapour pressure, and wind speed. With wind omitted, the result represents still air.
- Apparent Wind Angle Calculator Compute the apparent wind angle from true wind speed, boat speed, and true wind angle.
- Apparent Wind Speed Calculator Compute the apparent wind speed from true wind speed, boat speed, and true wind angle.
- Backstay Tension Guide Suggest backstay tension from backstayPercent = min(100, max(10, round(apparentWindKt * 4))).
- Ballast Ratio Calculator Compute a sailboat's ballast ratio using ballastRatioPercent = ballastWeightPounds / displacementPounds * 100.
- Beaufort Scale Lookup Look up the Beaufort wind force from zero to twelve for a wind speed in knots using standard inclusive upper bounds.
- Berth Depth Check Check whether a marina berth holds enough water by adding the height of tide to the charted berth depth and comparing against the vessel draft.
- Boom Force Calculator Compute the compression force on the boom from sheet tension via torque balance about the gooseneck.
- Bowsprit Compression Load Compute the ideal axial compression required to balance a forestay load at a specified angle to the deck.
- Bridge Clearance Calculator Compute the vertical margin under a chart-datum bridge clearance by subtracting both height of tide and vessel air draft.
- Capsize Screening Factor Calculator Compute the capsize screening factor; below two indicates better resistance to capsize.
- Ceiling Category Lookup Classify a cloud ceiling as low below five hundred feet, marginal below three thousand feet, or otherwise fine for visual flying rules.
- Chain Catenary Sag Calculator Estimate the catenary sag of anchor chain between two points from its weight per meter, span, and horizontal tension using a parabolic approximation.
- Code Zero Wind Angle Estimate the true wind angle for a code zero using codeZeroTwaDeg = round(50 + apparentWindKt * 0.3), clamped to 40 through 70 degrees.
- Comfort Ratio Calculator Compute Ted Brewer's motion-comfort ratio from displacement, waterline length, and length overall. When LOA is omitted, it is assumed equal to LWL.
- Compass Deviation Lookup Calculator Interpolate magnetic compass deviation between a vessel's cardinal calibration values. The defaults reproduce the included example card and should be replaced with the vessel's own swing data.
- Corrected Depth Calculator Add the height of tide to the charted depth sounding to obtain the actual depth of water.
- Corrected Waypoint ETA Compute ETA along a waypoint track while allowing for current: the boat first cancels the cross-current component, and its remaining along-track speed is combined with the current's along-track component.
- Course Over Ground Calculator Calculate the resulting course over ground from vessel motion combined with current set and drift.
- Course to Steer With Current Calculator Compute the heading to steer that compensates for a known tidal stream to achieve a desired track.
- Crew Drift Estimate Estimate how far an overboard crew member drifts as current speed times time in the water plus wind speed times time scaled by a one percent windage coefficient.
- Cross Track Error Calculator Calculate the signed perpendicular distance from a desired course given distance run and the bearing back to the start point.
- Cunningham Tension Guide Suggest cunningham tension from cunninghamPercent = min(100, max(0, round((apparentWindKt - 8) * 6))).
- 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.
- Current Gain Loss Calculator Calculate the distance gained or lost to the current along the course, with a favorable set positive and an adverse set negative.
- Current Shear Gain Compute the signed current shear across the boundary between the near surface layer and the deeper layer as the near surface speed minus the deeper layer speed.
- Day Shape Visibility Range Calculate the distance at which a day shape subtends a chosen recognition angle. Weather, contrast, eyesight, and obstructions can reduce actual recognition range.
- Dead Reckoning Position Calculator Project a dead reckoning position from a start coordinate, course, and distance traveled.
- Displacement Length Ratio Calculator Compute the displacement-to-length ratio; below two hundred is light, above three hundred is heavy.
- Distance to Layline Calculator Calculate the distance along the course centerline to a layline from the lateral offset and half of the total angle between port and starboard tacks.
- Douglas Sea State Lookup Look up the Douglas sea state from zero to nine for a significant wave height in meters using standard inclusive upper bounds.
- Downwind AWA Guide Guide the downwind target apparent wind angle as one hundred fifty degrees plus three tenths of the wind speed, clamped between one hundred thirty five and one hundred seventy degrees.
- Downwind VMG Calculator Compute downwind velocity made good as target boat speed times the absolute cosine of the true wind angle.
- 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.
- EP With Leeway Estimate the course made good by applying leeway to the true heading, subtracting the leeway angle on the starboard tack and adding it on the port tack.
- EPIRB Satellite Footprint Radius Calculate the geometric horizon footprint of an EPIRB search-and-rescue satellite from its orbital altitude. Actual detection also depends on the satellite network, beacon view, and link conditions.
- Expanding Square Leg Length Determine the first leg length of an expanding square search pattern so the squared spiral reaches the requested search radius after two legs from the datum.
- Favored End Calculator Identify which end of the start line is favored by comparing the time to sail the line against the true wind direction.
- Favored Tack From Shift Determine the favored tack from a signed wind shift where a positive shift lifts the starboard tack and a negative shift lifts the port tack.
- Ferry Glide Course Calculate the heading to steer so cross current lets the boat ferry glide onto the desired course, correcting by the arcsine of the current to boat speed ratio signed by the side the current comes from.
- Figure Eight Recovery Time Estimate the minutes to sail two circular lobes of a figure-eight recovery path at the given boat speed, plus the final approach allowance.
- Fog Risk Spread Check Assess fog risk from the temperature dew point spread; a spread of two degrees Celsius or less indicates conditions favourable for fog formation.
- Forestay Sag Calculator Compute forestay sag with the parabolic approximation sagMeters = transverseLoadPerMeterKg * 9.80665 * stayLengthMeters^2 / (8 * tensionNewtons).
- Frictional Resistance Compute frictional hull resistance using frictionalResistanceNewtons = 0.5 * 1025 * speedMs^2 * wettedAreaM2 * frictionCoefficient with a default coefficient of 0.004.
- Froude Number Calculator Compute the Froude number using froudeNumber = speedMs / sqrt(9.80665 * lengthMeters).
- Fuel At ETA Calculator Compute the liters of fuel burned by the time of arrival as the burn rate in liters per hour times the ETA in hours.
- Fully Developed Wave Height Estimate deep-water significant wave height for a fully developed sea as 0.21 U²/g, converting the supplied wind speed from knots to meters per second.
- Gale Warning Check Check whether a wind speed in knots reaches gale force, meaning Beaufort force eight to nine between thirty-four and forty-eight knots.
- Gennaker Tack Load Estimate the tack line load of a gennaker using tackLoadNewtons = 0.06 * windSpeedMs^2 * sailAreaM2 with a documented gennaker load coefficient.
- Great Circle Distance Calculator Calculate the great circle distance in nautical miles between two geographic positions.
- Gybe Distance Calculator Compute the distance sailed during a gybe to cover a given lateral offset.
- Gybe Loss Distance Estimate the distance lost to gybing from the number of gybes, boat length, and boat lengths lost per gybe.
- Gybing Angle Calculator Calculate the course change through a gybe as twice the sailing angle away from dead downwind.
- Handicap Allowance Calculator Compute the signed per-mile handicap allowance as your rating in seconds per mile minus the opponent rating in seconds per mile.
- Header Lift Detector Classify an upwind wind change as a header or a lift by comparing the current true wind angle with a baseline.
- Heel Angle Calculator Estimate the steady heel angle from heelDeg = degrees(asin(min(1, heelingMomentFtLb / (displacementPounds * metacentricHeightFeet)))).
- Heel Target Guide Guide the upwind heel angle as eight tenths of the wind speed in degrees, clamped between five and thirty degrees.
- Helm Balance Ratio Express the signed longitudinal separation between sail-plan center of effort and center of lateral resistance as a percentage of length overall.
- Horizon Dip Calculator Compute the dip of the visible horizon in minutes of arc as the coefficient zero point nine seven times the square root of height of eye in feet.
- Horizon Distance Calculator Compute the distance to the visible horizon in nautical miles as the coefficient one point one seven times the square root of eye height in feet.
- 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.
- IRC Corrected Time Calculator Compute IRC corrected time by multiplying elapsed time by the boat's published time correction coefficient (TCC).
- Jib Area Calculator Calculate the triangular jib area from the I and J mast and deck measurements.
- Jib Aspect Ratio Compute the jib aspect ratio as aspectRatio = iMeasurementMeters^2 / jibAreaM2 using the forestay height I and the measured jib area.
- Jib Car Position Calculator Compute a jib-car reference position as a selected percentage of foot length, measured aft of the clew. Final trim still depends on clew height and sheeting geometry.
- Jib Halyard Tension Guide Guide jib halyard tension using a rule of thumb of eight kilograms force per knot of apparent wind converted to newtons.
- Jib Lead Angle Guide Suggest jib lead angle from leadAngleDegrees = min(25, max(5, round(apparentWindKt * 0.8))).
- Jib Overlap Percentage Compute jib area as a percentage of foretriangle area. This is an area-ratio proxy; formal LP overlap percentage requires the luff-perpendicular and J dimensions.
- Jib Sheet Load Calculator Estimate the jib sheet load from dynamic pressure on the sail area divided by the sine of the sheet angle.
- Keel Aspect Ratio Compute the keel aspect ratio as keelAspectRatio = draftMeters^2 / keelAreaM2; deep fin keels have high ratios.
- Keel Lift Calculator Compute the hydrodynamic lift generated by a keel from boat speed, keel area, and a lift coefficient.
- Layline Distance Calculator Compute the distance along a layline to the mark given the lateral offset and tack angle.
- Lead Percentage Calculator Compute sail lead as leadPercent = centroidDistanceMeters / waterlineLengthMeters * 100; signed distances allow the centroid to fall aft of the reference.
- Lee Bow Effect Calculator Project current onto the desired course as current speed times the cosine of the relative angle. This along-course proxy does not model the true lee-bow effect, which also depends on heading, boat speed, and apparent wind.
- Leeway Angle Calculator Estimate leeway angle with the empirical relation leeway = K times heel divided by boat speed squared. Calibrate K for the hull, keel, and knot-based speed data in use.
- Light Range Corrected Correct a navigation light's nominal range for prevailing meteorological visibility using Allard's inverse-square and atmospheric-transmission relation. Nominal range is defined at ten nautical miles of visibility.
- Lighthouse Geographic Range Calculator Compute the geographic range at which a light becomes visible as one point one seven times the sum of the square roots of observer and object heights in feet.
- Lock Water Volume Calculator Compute the volume of water moved by a lock filling or emptying as the chamber length times width times the water level change.
- Main Aspect Ratio Compute the mainsail aspect ratio as aspectRatio = luffLengthMeters^2 / mainsailAreaM2; taller narrower sails have higher ratios.
- Main Halyard Tension Guide Guide mainsail halyard tension using a rule of thumb of twelve kilograms force per knot of apparent wind converted to newtons.
- Main Sheet Load Calculator Estimate the main sheet load from dynamic pressure on the sail area divided by the sine of the sheet angle.
- Mainsail Area Calculator Compute the triangular mainsail area using mainsailAreaM2 = 0.5 * luffLengthMeters * footLengthMeters.
- Mainsail Twist Guide Suggest mainsail twist from twistDegrees = min(45, max(5, 60 - apparentWindKt)).
- Maneuver Time Loss Compute the total time and distance lost to a series of maneuvers from the maneuver count, seconds lost per maneuver, and boat speed.
- Mast Bend Calculator Compute mast bend from bendMeters = mastHeightMeters * bendPercent / 100.
- Mast Rake Calculator Compute mast rake from the horizontal masthead offset and the vertical distance between the masthead and the lower measurement point.
- Metacentric Height Calculator Compute the metacentric height using metacentricHeightFeet = keelToCenterBuoyancyFeet + buoyancyToMetacenterFeet - keelToCenterGravityFeet (GM = KB + BM - KG).
- MOB Drift Distance Estimate the maximum down-drift distance when current and windage act in the same direction. Vector set and wind directions are required for a position estimate.
- Mooring Windage Load Calculator Compute the wind load on a moored vessel from wind speed, windage area, and drag coefficient.
- Opposite Tack Course Calculator Calculate the corresponding course on the opposite tack by reflecting the current course across the true-wind direction.
- Opposite Tack Layline Bearing Calculate the bearing of the opposite tack layline by offsetting the true wind direction by the tacking angle to the chosen side of the wind.
- ORC Corrected Time Calculator Compute ORC time-on-time corrected time by multiplying elapsed seconds by the supplied Time Correction Coefficient (TCC).
- Oscillation Amplitude Compute half the shortest circular separation between the two extreme compass headings, including oscillations that cross north.
- Outhaul Tension Guide Suggest increasing outhaul tension as apparent wind rises, from twenty percent in very light air to full tension at twenty knots.
- Overfalls Risk Factor Estimate the severity of overfalls from the spring tidal range, maximum stream rate, and water depth.
- Overstand Distance Calculator Compute the extra distance sailed when overstanding the mark from the distance to the mark, overstand angle, and tacking angle.
- PHRF Time on Distance Calculator Compute a PHRF time-on-distance corrected time by subtracting the rating allowance over the course length from elapsed time.
- PHRF Time on Time Calculator Compute a PHRF time-on-time corrected time by scaling elapsed time with the coefficient six hundred fifty over five hundred twenty plus rating.
- Polar Performance Percentage Calculator Compare the achieved boat speed against the polar target speed as a percentage of target performance.
- Polar Target Speed Calculator Compute the polar target boat speed by multiplying true wind speed by an efficiency ratio.
- Portsmouth Yardstick Corrected Time Calculator Calculate a Portsmouth Yardstick corrected race time using correctedTimeSeconds = elapsedSeconds * 100 / pyNumber.
- Position Error Circle Estimate the radius of the position error circle from a compass steering error as distance run times the error in degrees divided by fifty seven point three.
- 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.
- Quickstop Return Course Calculate the reciprocal of the course at a man-overboard incident as a planning reference for the return leg. The actual Quickstop maneuver and final approach depend on wind, sea room, and the casualty's observed position.
- Range Ratio Calculator Compute the tidal range ratio from rangeRatio = springRangeMeters / neapRangeMeters.
- Reef Percentage Calculator Compute the percentage of sail area reduced when sailing on a reefed headsail or mainsail.
- Reefing Wind Speed Calculator Calculate the apparent wind speed at which to reef using reefWindKt = designWindKt * reefFactorPercent / 100.
- Righting Arm GZ Calculator Approximate the initial-stability righting arm as GZ = GM sin(heel) for heel angles no greater than fifteen degrees; use a vessel's measured GZ curve at larger angles.
- Righting Moment Calculator Compute the righting moment in pound-feet as righting arm times displacement; a negative arm yields a capsize moment.
- Roach Area Calculator Estimate the mainsail roach area as roachAreaM2 = 0.5 * luffLengthMeters * footLengthMeters * roachPercentage / 100 of the triangular sail area.
- Rudder Aspect Ratio Compute the rudder aspect ratio as rudderAspectRatio = depthMeters^2 / rudderAreaM2; high ratio rudders are deep and narrow.
- Rudder Correction Angle Calculator Compute the rudder correction angle from correctionDeg = degrees(atan(lateralDriftMs / forwardSpeedMs)).
- Sail Area Calculator Compute the triangular mainsail area from the luff (P) and foot (E) measurements.
- Sail Area Displacement Ratio Calculator Compute the sail area to displacement ratio; above fifteen indicates good light-air performance.
- Sail Drag Force Calculator Compute aerodynamic sail force from forceNewtons = 0.5 * 1.225 * windSpeedMs^2 * sailAreaM2 * dragCoefficient.
- Sail Load Calculator Estimate the aerodynamic load on a sail from wind speed and sail area using a flat-plate drag model.
- SART Detection Range Estimate the radar detection range of a search and rescue radar transponder as one point one seven times the sum of the square roots of the SART mounting height and the responding antenna height in feet, capped at forty nautical miles.
- Search Pattern Area Calculate the area swept by a square search pattern as the square of its side length.
- Secondary Port Correction Compute the secondary port height correction from the signed difference in tidal range and an interpolation proportion taken from almanac tables.
- Sector Search Leg Length Calculate the chord between successive radials of a sector search pattern as twice the radius times the sine of half the sector angle.
- Set and Drift Correction Calculator Calculate current set and drift by subtracting the vessel's through-water velocity vector from its observed over-ground velocity vector.
- Shift Rate Calculator Compute the signed rate of the shortest compass-direction change between two mean wind headings, correctly handling the wrap across north.
- Shroud Tension Calculator Compute the cap-shroud tension needed to balance a given forestay tension from the rigging head angles.
- Sound Signal Range Estimate the audible range of a vessel sound signal from its whistle output level in decibels using two nautical miles above one hundred and thirty decibels, one nautical mile above one hundred and ten, and half a nautical mile otherwise.
- Speed Over Ground Calculator Calculate the resulting speed over ground from vessel motion combined with current set and drift.
- Spinnaker Area Calculator Estimate the symmetric spinnaker area from the SL leech length and SMW width using the standard three-quarter approximation.
- 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.
- Spinnaker Tack Height Estimate how high the spinnaker tack can be raised below a fixed full-hoist head position from the unused fraction of the luff length.
- Spinnaker Wind Angle Range Look up the true wind angle band for carrying a spinnaker, with symmetric sails trimmed from 110 to 175 degrees and asymmetric sails from 95 to 155 degrees.
- Spring Neap Factor Calculator Compute the spring/neap modulation factor from factor = abs(cos(2 * PI * lunarAgeDays / 29.53)); one means spring tides and zero means neap tides.
- Start Line Bias Calculator Compute signed start line bias from biasSeconds = (lineLengthNm * 3600 / boatSpeedKt) * cos((lineBearingDeg - trueWindFromDeg) * PI / 180); positive favors the pin end.
- Start Line Length Rule Recommend a starting line length from the fleet size and average boat length using an adjustable scale factor.
- Storm Warning Check Check whether a wind speed in knots reaches storm force, meaning Beaufort force ten to eleven between forty-eight and sixty-four knots.
- Swing Circle Area Calculator Calculate the area a boat can sweep as a circle around its anchor from the anchor circle radius.
- Tack Distance Calculator Compute the distance sailed on one tack to cover a given lateral offset.
- Tack Loss Distance Estimate the distance lost to tacking from the number of tacks, boat length, and boat lengths lost per tack.
- Tacking Angle Calculator Calculate the tacking angle using tackingAngle = 2 * closeHauledAngleDeg from the close-hauled angle off the wind.
- Tidal Curve Height Interpolate a falling tide from high water to low water with a cosine curve over the specified high-to-low interval.
- Tidal Diamond Vector Calculator Resolve a tidal diamond set and drift into components along and across the boat's course.
- Tidal Race Speed Calculator Scale the published peak spring stream rate to the day's tidal range to estimate the speed of a tidal race.
- Tidal Stream at Time Calculator Model the tidal stream as a sinusoid and return its signed rate at a given time into the flood-and-ebb cycle.
- Tidal Stream Rate Calculator Compute the tidal stream rate from the distance a free-floating object drifted and the elapsed time.
- Tide Gate Window Calculator Calculate the hours needed to transit a tidal gate against an adverse current from the gate distance, boat speed, and current strength.
- Tide Height Cosine Curve Interpolate tide height on a cosine curve from heightM = lowWaterMeters + (highWaterMeters - lowWaterMeters) * (cos(PI * hoursFromHigh / 6) + 1) / 2.
- Tide Rule of Twelfths Calculator Compute the water level change for one hour of a tide using the rule of twelfths over a six hour half cycle.
- Time to Layline Current-Corrected Estimate the minutes remaining to the layline by dividing the current corrected distance to the layline by the velocity made good and converting to minutes.
- Time to Start Line Calculator Calculate how many minutes it takes to reach the start line from the remaining distance and current boat speed.
- Time to Tack Calculator Compute minutes until the layline from minutes = distanceToLaylineNm / boatSpeedKt * 60.
- Time to Waypoint Calculator Calculate sailing time to a waypoint in minutes using timeMinutes = distanceNm / speedKt * 60.
- Traveler Position Guide Suggest traveler position from offsetCm = min(30, max(-30, round((15 - apparentWindKt) * 2))); positive values are to weather.
- True Wind Angle Calculator Compute the true wind angle from apparent wind angle, boat speed, and apparent wind speed.
- True Wind Speed From Apparent Calculator Compute the true wind speed from apparent wind speed, apparent wind angle, and boat speed.
- UKC Calculator Compute the under keel clearance by subtracting the vessel draft from the depth of water.
- Understand Distance Calculator Compute the distance gained by footing below the layline from the distance to the mark, understand angle, and tacking angle.
- Upwind TWA Guide Guide the upwind target true wind angle as forty five degrees minus half the wind speed, clamped between thirty and fifty five degrees.
- Upwind VMG Calculator Compute upwind velocity made good as target boat speed times the cosine of the true wind angle.
- Vang Angle Calculator Compute the vang angle in degrees as atan of the mast attachment height over the boom attachment distance.
- Vang Tension Guide Suggest vang tension from vangPercent = min(100, max(10, round(windSpeedKt / maxWindKt * 100))) using the boat's maximum working wind.
- VHF Range Calculator Estimate very high frequency radio range over water as one point one seven times the sum of the square roots of the vessel and shore antenna heights in feet.
- Visibility Category Lookup Classify horizontal visibility in nautical miles into fog, poor, moderate, or good bands used in marine forecasts.
- VMG to Leeward Calculator Compute velocity made good to leeward from boat speed and true wind angle on a run.
- VMG to Waypoint Calculator Compute the velocity made good toward a waypoint given a heading offset.
- VMG to Windward Calculator Compute velocity made good to windward from boat speed and true wind angle.
- Waterline Length from Speed Calculator Estimate a hull's waterline length in feet from its hull speed using waterlineLengthFeet = (speedKt / 1.34) ^ 2.
- Wave Making Resistance Ratio Compute the wave making share of total hull resistance using wavemakingRatioPercent = waveResistanceNewtons / totalResistanceNewtons * 100.
- Wave Period Estimate Estimate the peak period of fetch-limited deep-water waves from wind speed and unobstructed fetch using the dimensionless SMB growth relation.
- Waypoint Rhumb Bearing Calculator Calculate the constant rhumb line bearing from one geographic position to another.
- Wetted Surface Estimate Estimate wetted surface from displacement using wettedSurfaceAreaM2 = displacementTonnes^(2/3) * wettedCoefficient with a default coefficient of 2.5.
- Williamson Turn Course Calculate the initial sixty-degree heading and final reciprocal course for a Williamson turn. After reaching the initial heading, reverse the rudder and steady on the reciprocal of the original course.
- Winch Handle Force Calculator Compute the handle force needed to trim a load as the load divided by the winch power ratio.
- Winch Power Ratio Calculator Compute ideal winch mechanical advantage as the handle-to-drum radius ratio multiplied by the dimensionless gear ratio. Real handle force is higher because this ideal model excludes friction.
- Wind Chill Calculator Compute the wind chill apparent temperature from the standard joint environment committee formula for cold and windy conditions.
- Wind Pressure on Sail Calculator Compute aerodynamic force on a sail from dynamic pressure using 0.5 times air density times wind speed squared times sail area times lift coefficient.
- Wind Shift Gain Calculator Estimate the lateral gain from a persistent wind shift over the distance sailed, with positive lifts gaining and headers losing.