I have a log of every fuel purchase with location, date, gallons, engine hours from the day we purchased the boat and hours between fuelings. It in excel so running some calculations is easy. Fuel burn averaged from day one, the long average. Average for each topping off. Dollars spent on fuel and so on.
We cruise at two speeds, either eight knots or fifteen. There’s always engine time at low rpm, entering and leaving marinas, no wake zones, trolling, idle time, etc that offsets the cruise speeds. So, while I can’t tell you accurately how much fuel I’m burning at any given rpm, I can use the date to plan a trip. For instance, the long average, over 1200 hours, is about six gph. If I’m planning on an eight knot speed because I’m traveling with some eight knot boats, I plan ten to eleven gph. If we have a long rum where we will be at around fifteen knots, I generally estimate thirteen to fifteen gph. Yes I’m burning more gallons per hour, but I’m getting there in about 60% of the time.
It’s about learning how your boat behaves so you can predict how it’s going to perform.
We are doing a four hundred mile trip in a few weeks and I plan on using my often overlooked miles traveled feature on my gps. I have four fuel stops planned, all with a working estimate of less than 200 gallons based on a one mile per gallon burn. The capacity is 300 gallons, so I’ve got plenty of margin.
It’s old school and it takes practice, but if I run out of fuel it will not be because of a faulty gauge.
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