Sam,
on my older Lowrance plotter I can set a threshold speed for my distance log. Make it 3knots or something then all of your drifting won't count in the distance log of your plotter.
Part 1
With older gear without backbone setup the triducer on my Furuno (old) gives a reasonable indication of distance traveled given that you allow for tides and current (already some errors) and when you add in the question mark about how full the tank was (based on the angle of the boat hull when you poured fuel in) and then add in the hours run (off your watch or the hour meter s;with two motors) you can guesstimate the fuel you used.
Part 2
To be sure, to be sure (Irish consideration) when you return to home port, you then add a known quantity of ULP91 through a filter funnel (to catch water and other gunk) and see how close your guesstimate was in part one above was.
The above methodology takes into consideration the questionable readings given by the fuel sender and gauge, how high or low the bow was when you last filled the tank and the myriad other factors like wind and tide and current and the speeds you ran at during the "cruise"
My fuel usage / economy is a range rather than a precise number and if in doubt I just carry a few extra drums.
Lifes too short to stuff a mushroom so as they say in Qld "Don't you worry about that!"
PS the other method is ti use a dip stick but too hard on the Vag.
What could go wrong.......................
Yes - your motor is too old but you can run an in line fuel flow sender like these
https://buy.garmin.com/en-AU/AU/p/11561
Navico also make one if you use lowrance or Simrad. You also need a compatible NMEA2000 display if you don't already have one and a backbone starter kit. If you need to buy all of it it gets pricey but I guess it depends on just how badly you want the info
I have a Garmin 75
For all the bother and money, I think I’ll just do some rough sums and work it out.
Thanks for the info my friend
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