CALCULATING TIME, SPEED &
DISTANCE
2011
Time / Distance / Speed
Calculations
Time / Distance / Speed
Calculations
• All these calculations revolve around the following
formula
60D = T
S
Time / Distance / Speed
Calculations
• T = time in minutes
• S = speed in knots
• D = distance in nautical miles
60D = T
S
Calculating an ETA
Calculating an ETA
• Measure the distance along the course line to the
destination in nautical miles
Calculating an ETA
Calculating an ETA
• The distance from Ladysmith (top left hand corner) to
off Norway Island is 12.9 nautical miles.
• Using
60D = T
S
• 60 x 12.9 = T in minutes = 25.8 minutes
30
Calculating an ETA
• Add this time to the the departure time, e.g. 0800 LT,
and your ETA off Norway Island will be around 0825
LT.
6 Minute Finger Method
6 Minute Finger Method
• This method may be used with either dividers or
fingers held a set distance apart for a rapid
estimation of distance.
6 Minute Finger Method
• At 30 knots the vessel will travel 3 nautical miles
every 6 minutes.
• Set dividers to 3 nautical miles on the latitude scale,
and then run them down the course line counting off
6 minutes as you go.
6 Minute Finger Method
6 Minute Finger Method
• Alternatively put two fingers over the 3 nautical miles
on the latitude scale, and then run them down the
course line counting off 6 minutes as you go.
• This will give you somewhere around 24 minutes plus
for a time travelled.