Hey guys I wanted to add my method for estimating fuel usage. Keep in mind I'm still pretty new so some of my tricks could be common knowledge for some of you.
I recently turned my realism up with fuel being one of the aspects. I spent the whole game so far planning to up the realism so I'm already in the habit of using the "half speed" setting to save fuel. Anyway I set course and left port and soon realized, I have no idea how far I can go regardless of speed setting.
Then I did what any good Captain would do: Keep calm and use math!
So I looked at my fuel gauge and was at 98%.
I then used the ruler to measure how far I'd traveled from port, 321 Km at half speed. Then using the formula of "321km=2% fuel", I broke down my plotted path into 321 Km sections all the way to my destination.
I came up with an estimate of 89% fuel remaining upon reaching my destination over a course of 1950 Km.
When I reached my assigned destination, I had 89% fuel remaining right on the money.
Fuel usage will of course change and be harder to estimate if you need to put the boat through maneuvers, or have to change speeds.
Hope this is helpful! Happy hunting!