Calculating Time using a Nautical Chart:

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