Calculating Time using a Nautical Chart:

The Electronic Way:

Many chart plotters will automatically calculate your Estimated Time of Arrival (ETA) and display the remaining time to reach your destination (often called "Time to Waypoint" or "Time to Go") once you've entered your destination or route.

Important considerations

  • Speed Over Ground (SOG): This is generally the most important speed for calculating travel time as it accounts for the effects of current and wind on your vessel's actual progress over the ground. Speed through water (STW) might be different due to these external factors.
  • Dynamic Conditions: Remember that conditions like wind and currents can change during a passage, affecting your SOG and therefore your ETA. Be prepared to adjust your route or speed accordingly.
  • Checking your Progress: It's good practice to periodically check your actual progress against your planned route and make adjustments as needed to ensure you stay on course and arrive on time.

The Traditional Way:

Formula:

1 knot = 1 nautical mile per hour

 

D ÷  S  = Time (in decimals of an hour)

To convert the decimals into minutes x 60

 

An example: 

How long will it take to travel 3.2 nautical miles at 10 knots? 

3.2  ÷ 10 knots = 0.32 x 60 = 19.2 minutes 

 

Fuel Consumption: (Power Vessels) 

Dependant  on your speed, engine type, horsepower etc. 

 

But a good rule of thumb is 1/3 out, 1/3 back and 1/3 in reserve