Estimate hours remaining and nautical-mile range from usable fuel, burn rate (GPH), and cruise speed. Hold a reserve — sea state often burns more than the book.
Usable fuel is tank capacity minus your reserve. Hours are usable gallons divided by GPH. Range multiplies hours by cruise speed in knots.
usable_gal = tank × (1 − reserve%/100)
hours = usable_gal ÷ GPH
range_nm = hours × speed_kn
Pickup height and trim mean you cannot run a tank bone-dry. The reserve percent is your safety buffer (rule of thirds is common for open water). Wind, load, and fouling can raise burn 15–30%. Use a measured flow meter or logged trip burn when you have it. Volume/KD: unknown.
One third outbound, one third return, one third untouched. That is a 33% reserve on a round-trip plan. Short protected day trips sometimes use 10–20% instead — your call, not this page’s.
Start with the published capacity, then subtract reserve. If you know pickup leaves gallons unusable, fold that into a higher reserve or enter a lower tank number.
Best: flow meter at cruise RPM. Next: logged gallons ÷ hours. Last: HP-based estimates. This tool does not invent burn from horsepower.
Range is in nautical miles when speed is in knots. Statute miles ≈ NM × 1.15078.