Great Circle & Rhumb Line Tool Distance, Course, Waypoints & ETA

Great Circle • Rhumb Line • Distance • Initial / Final Course • Waypoints • Antimeridian • ETA • Via Points • Current-Aware Speed Screen

Great Circle & Rhumb Line Tool Distance, Course, Waypoints & ETA

Compare the shortest great-circle route with a constant-course rhumb line, generate passage waypoints and estimate arrival time. Simple mode compares both routes between two positions. Advanced becomes a multi-leg voyage geometry model with per-leg great-circle/rhumb selection, via points, generated sub-waypoints, speed overrides, STW/current course-to-steer screening, weather speed factor, schedule margin, stop delays, antimeridian handling and latitude-limit review.

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Need via points, per-leg route modes, currents or a detailed ETA profile? Click Advanced above.Simple compares direct spherical great-circle and Mercator/rhumb-line solutions and generates waypoints for the selected planning route.

DirectGC vs rhumb comparison

OutputCourse, distance, waypoints & ETA

GlobalAntimeridian-safe longitude handling

Direct Passage

Departure latitudeDecimal degrees, North + / South −.

Departure longitudeDecimal degrees, East + / West −.

Destination latitude

Destination longitude

Planning speed over groundknots.

Departure date/time UTCInterpreted as UTC.

Waypoint route

Waypoint spacingNM between generated planning points, approximately.

Voyage Timing & Waypoint Generation

Departure date/time UTC

Default speed basis

Default planned SOGknots, used for SOG basis.

Default STWknots, used for STW + current basis.

Current set°T, direction current flows toward.

Current driftknots.

Weather / operating speed factor% applied to planned SOG or solved SOG.

Sailing-time margin% added to underway time after speed factor.

Fixed voyage delayhours for pilotage, traffic, etc.

Generated waypoint spacingNM approximate maximum spacing for route display and current-aware sublegs.

High-latitude review thresholdabsolute latitude degrees.

Maximum allowed route latitudeAbsolute latitude planning screen. Does not construct a composite great circle.

Via-Point / Segment Register

Each row is a route control point. Segment settings on a row apply from that point to the next point. Use Great Circle for shortest spherical segments, Rhumb for constant-course segments. Speed override > 0 replaces the default SOG/STW magnitude for that segment. Stop delay is applied after arrival at that point, except the final point.

Latitude	Longitude	Segment to next	Speed override kn	Stop delay hr

Voyage Geometry Checks

Positions verifiedLat/lon correspond to safe charted route control points. Land / restricted waters checkedMathematical route is not assumed clear of land, TSS, ice or exclusions. Great-circle waypoints transferred / checkedIntermediate course changes and chart projection are reviewed. Speed basis realisticSOG or STW/current assumptions fit the voyage condition. Weather / ocean routing reviewedShortest mathematical route is not automatically safest/fastest operational route. High-latitude / ice limits reviewedProjection and operating constraints are independently assessed. Dateline / longitude convention checkedEast-positive / West-negative positions and antimeridian crossing are understood. ETA assumptions documentedSpeed factors, time margin, stops and fixed delays are visible to the bridge/operations team.

Navigation limitation: this is a spherical route-geometry and voyage-timing screen, not an approved route-planning/ECDIS system. Great-circle and rhumb-line solutions do not check land, charted dangers, traffic separation schemes, weather, ice, piracy/security areas, draft/UKC, regulatory routing or ENC safety contours. Generated waypoints must be transferred and independently verified using approved navigation systems and current publications.

Navigation basis: Bowditch distinguishes great-circle sailing, which follows the shorter arc of a great circle and minimizes spherical distance, from Mercator/rhumb-line sailing, which maintains constant course. NOAA notes that a straight line on a Mercator nautical chart is a rhumb line/loxodrome of constant course. The tool uses a spherical Earth with mean radius 3,440.065 NM, shortest-longitude wrapping, great-circle spherical interpolation for waypoints and standard Mercator logarithmic-latitude rhumb mathematics.

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