Join Date: Jan 2006
Location: living aboard since 1972
Thanked 12 Times in 12 Posts
Rep Power: 12
There can be no standard unit to represent volume as the fuels tanks on different boats differ.
First make sure that you can insert a "Stick" to measure volume. Many fill hoses are not straight drops to the bottom of the tank. If you can insert a stick to the bottom of the tank and the tank is uniform in its vertical dimensions; then, it is possible to insert the unmarked stick after filling the tank and mark the full indication at the fluid spot after withdrawing. This can be divided as you please into half, quarters, etc.
If your tank is not uniform in vertical dimension; then, I believe your only choice would be to start with an empty tank, add known quantities of fuel and mark the stick at these intervals. Good luck!