"JoeSpareBedroom" wrote in message
...

Let me rephrase the question, to find out how many miles is involved in
this trip:

In the boating course, how did they instruct you to estimate how much fuel
you would burn?

re 'Boating Course' Student's Notes 8th edition 1999
Section 11.3 The Fuel Supply

The fuel supply should be checked to ensure that there is enough for the
journey, or that fuel can be obtained en route. Running out of fuel is the
single most frequent emergency that boaters experience. Every hour, a marine
engine can be expected to use 0.6 liters of fuel for each kW. In practical
terms, a 75 kW gasoline outboard motor on a 6m cruising boat will give about
1 kilometer per litre of fuel. larger boats and larger engines use more;
diesel engines use less, but all boats use more fuel when travelling against
a head wind and adverse current. If possible, the up-wind and up-current leg
of a journey should be completed first, as it is then easier to return. A
good maxim for fuelling is one-third out, one-third back, and one-third in
reserve.

note: Not sure if this section has been updated since.