Sixty miles at six knots
A 60-nautical-mile route at a constant six knots produces ten underway hours. Adding one fixed hour and ten percent contingency adds another two hours in total, producing a twelve-hour planning duration.
Boat Speed, Distance, Time & ETA Calculator
Created by: Emma Collins
Last updated:
Solve marine speed, nautical distance, or underway time and add departure, delay, and contingency inputs for a transparent passage ETA.
Boat Speed, Distance, Time & ETA Calculator
BoatingSolve nautical passage arithmetic and keep underway time, delay, contingency, and ETA visibly separate.
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Browser local time; verify the operational time zone.
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What is a Boat Speed, Distance, Time & ETA Calculator?
A Boat Speed, Distance, Time & ETA Calculator solves one missing marine travel variable from the other two, then separates underway time, fixed delays, contingency, and departure time to produce a transparent planning ETA. Results also show kilometres, statute miles, miles per hour, and kilometre-per-hour conversions without creating another standalone knots converter.
The core relationship is simple because one knot means one nautical mile per hour. Sixty nautical miles at six knots takes ten hours under a constant-speed assumption. That arithmetic becomes misleading when users call the result a guaranteed arrival rather than a baseline scenario.
A realistic passage can include harbour speed limits, manoeuvring, adverse or favourable current, sail changes, weather, sea state, traffic, locks, bridges, tide gates, rest, fuel stops, detours, and equipment problems. The calculator exposes fixed delay and percentage contingency so some uncertainty is visible, but detailed legs and current information still belong in the passage plan.
RYA passage-planning guidance emphasizes route, tides and currents, dangers, constraints, refuge, daylight, weather, boat limitations, engine, crew, and sharing the plan. An ETA is one element of that wider process. It should be revised using observed progress rather than defended after conditions change.
How the Boat Speed, Distance, Time & ETA Calculator Works
When time is unknown, distance is divided by speed. When distance is unknown, speed is multiplied by time. When speed is unknown, distance is divided by underway time.
Contingency hours equal underway hours multiplied by the entered percentage. Fixed delays are added separately so a lock or bridge wait is not confused with slower travel.
If a departure date and time is supplied, total planning hours are added to create the ETA. The browser’s local time interpretation is used, so the user must verify time zone and daylight-saving context.
Scenario rows vary speed around the solved value while holding distance and delay assumptions constant. They show sensitivity, not a forecast that the boat will achieve those speeds.
Formulas and assumptions
Time = distance ÷ speed
Distance = speed × time
Speed = distance ÷ time
Contingency = underway time × contingency %
ETA = departure + underway + fixed delay + contingency
Example Calculations
Required average speed
If a verified 36-nautical-mile route must be covered in six underway hours, the arithmetic speed is six knots. That does not establish that the vessel can safely maintain six knots in the expected conditions.
Midnight arrival
A departure at 18:00 with an eight-hour total scenario produces an ETA at 02:00 the next day. The plan must address darkness, fatigue, lights, arrival hazards, berth access, and a safe alternative if delayed.
Common Applications
- Producing a first-pass marina arrival scenario.
- Converting a charted route distance into underway hours.
- Checking the arithmetic average speed required for a user-entered time.
- Separating bridge or lock waiting from travel time.
- Comparing slow, planned, and faster speed scenarios.
- Teaching the exact relationship between knots, nautical miles, and hours.
Passage-Planning Tips
Use route distance from current appropriate chart work, not merely a straight-line website measurement. Break passages into legs when harbour, offshore, sailing, and motoring speeds differ.
Keep UTC, local time, daylight saving, tide-table time, and gate time consistent. Write the time zone next to every operational time in the passage plan.
Recalculate with actual speed over ground and remaining verified route distance. If conditions or crew capability deteriorate, revise or abandon the plan rather than chasing the original ETA.
Frequently Asked Questions
How do I calculate boat travel time in nautical miles?
Divide nautical miles by speed in knots. A 60-nautical-mile passage at a constant six knots takes ten underway hours. Real elapsed time can be longer because speed varies and routes include manoeuvring, current, weather, traffic, locks, bridges, fuel stops, waiting, and contingency. Enter those separately instead of hiding them inside speed.
What is the difference between underway time and total planning time?
Underway time is distance divided by the entered constant speed. Total planning time adds fixed delays and a percentage contingency based on underway time. The separation helps users see which assumption creates the ETA. Neither time predicts actual conditions or relieves the skipper from updating the passage plan.
Should I use speed through water or speed over ground?
Use speed over ground when converting a charted ground distance directly into an ETA scenario. Speed through water requires a separate current-vector correction before it represents progress over the ground. Label the source of every speed and avoid averaging incompatible GPS, log, motoring, sailing, harbour, and offshore observations.
Can the calculator determine a safe boating speed?
No. COLREG safe speed depends on visibility, traffic, manoeuvrability, background lights, wind, sea, current, hazards, draft, radar limitations, and other prevailing circumstances. This calculator performs arithmetic with a user-entered planning speed; it never decides whether that speed is safe or lawful.
Why add a contingency percentage?
Contingency makes uncertainty visible. It can represent conservative allowance for variable speed or minor delays, but it does not replace scenario-specific route legs, weather margins, tide gates, daylight constraints, or alternate plans. Choose and document the percentage rather than treating the default as an official recommendation.
How should I handle overnight or multi-day ETAs?
Enter a departure date and time so the result advances across midnight and calendar days. Confirm the device time zone and daylight-saving setting before interpreting the displayed ETA. Marine broadcasts, tide tables, gate times, and logs may use UTC or another zone, so all inputs must share a clearly documented time basis.
Sources and References
- Royal Yachting Association. Passage Planning, accessed July 16, 2026; https://www.rya.org.uk/water-safety/passage-planning-and-navigation/passage-planning/.
- U.S. Coast Guard Navigation Center. Amalgamated International and U.S. Inland Navigation Rules, current online edition accessed July 16, 2026; https://www.navcen.uscg.gov/navigation-rules-amalgamated.
- NOAA Office of Coast Survey. Nautical charts, Coast Pilot, and chart education, accessed July 16, 2026; https://www.nauticalcharts.noaa.gov/.
- NOAA National Weather Service. Marine Forecast and Safe Boating resources, accessed July 16, 2026; https://www.weather.gov/safety/safeboating-marine.
- International nautical-mile definition and spherical/vector formulas documented in the calculator method.
Navigation limitation
The ETA is constant-speed arithmetic from user inputs. It is not a forecast, safe-speed determination, route approval, daylight check, weather assessment, or promise of arrival.