Hi guys. I have just purchased a 1979 superamerica 48. Maiden voyage bringing her home at average 17.5 knots. Just over 2 hours running. The fuel gauges read when we left between 1/2 and 3/4. First hour and a half running was great appeared to not be using much as needles hardly moved. Last half hour they dropped to just above empty? Hoping this is not accurate? Running twin Cummings 903. Could anyone enlighten me to a average litre per hour running cost please.?