We ran the engine for 2-3 hours each day so that we could charge the batteries, run the watermaker and boost the fridges.  While we were at it we put it in gear and added an extra knot or two to our speed.

We have 200 litres of diesel in the tank and 80 litres in jerry cans.  We (or rather Kit and Mike) took advantage of a slightly flatter few hours to top the tanks up. 

In total we ran the engine the 97 hours including one 36 hour period when we had no wind.  In the end we used 145 litres for the passage.