Extra weight and fuel consumption

[cliffdale]

It takes just under 4 hours to make a Falmouth to Guernsey trip. Does it make much difference to the fuel consumption to carry full water tanks, about 140 litres across the channel?
I have often wondered whether to mostly empty the water tank on passages. It must be like carrying 2 more passengers.

Is it worth unloading the water or dont bother??
Cliff

 

[Deleted User YDKXO]

Depends on the boat but it certainly makes a difference on my boat. My water tank carries 700litres and thats 700kg of uneccessary weight to push along so unless we're going somewhere where we can't get water, I always try to leave the water tank near empty for a long passage as it's worth 1-2kts speed

 

[Chill]

fill her up with fuel then for return journey empty water tank. Makes sense to cruise with empty water tanks.