These are straight forward speed, distance, time calculations.
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1. 45 miles to run
Speed 13 kts plus 2 kts of tidal stream = 15 kts
45 divided by 15 = 3
Arrival time - 0830 + 3 hrs = 1130
2. Speed made good 32kts
Time taken 48 mins
32 x 48 = 1536 divided by 60 to bring it back to hrs = 25.6nm
To check it I used the rule of 6th’s at 32 kts I will cover 3.2 in 6 mins (divide by 10) 48 divided by 6 (mins at 3.2kts) = 8 8 x 3.2 = 25.6
Sometimes it is easier to reduce the speed to rule of 6th’s straight away.
3. Distance 35nm time 1 hr 15 mins
I find it easier to convert to minutes rather than trying to work out what decimal bits of an hr it is e.g if the time was 1 hr 39 mins what is the 39 as a decimal of 1? (If you got 0.65 - great).
35 divided by 75 mins = 0.46666667 per min
x 60 to get it back to hrs = 28 kts
If you are happy to do the calculation as a decimal, it would be 35 divided by 1.25
Next time you are in the car and pass the how far away signs - have a try at the calculations.
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