First time boat owner... have taken my 18 foot baron out on the ocean... very smooth day... maybe 6km tops past Garden Island which is probably 12-14 miles from where we launched... we have used what I think is an incredible amount of fuel??? 60 -65 litres.... is this to be expected from a 1996 engine?? Averaged around 20 -25 knots cruising. Any ideas what could be causing this??? Any help will be appreciated.