From: Bellevue, NE
The table above shows you the pertinent efficiency info Fuel/Mile and cargo(F/M). Higher numbers are better for Cargo(F/M) and lower is better for fuel/mile.
I believe Cargo (M/F) is the right measure, here.
re speed, I think the general idea is that if you double cruise speed, you divide by two the number of convoys at sea at any given time, and therefore fuel usage (convoys loading and unloading are docked, and use no fuel). So perhaps the correct "unit of efficiency" for shipping lane fuel usage (under constraint of port load rates) would be something like
Cargo size x Speed x Endurance / Bunker capacity
under constraints (one day loading/unloading time)
ship tonnage < min ship port rate
nr of ships in convoy < min dock size / ship tonnage
nr of ships in convoy < min total port rate / ship tonnage
(interestingly, the unit here is something like squared miles per hour which corresponds to viscosity in fluid mechanics, not sure how to interpret this...)
Actually, this is very close to what the railroad industry uses to measure the efficiency of a train. I think it is also the right measure that we are after. Very good job Francois Let's make an example so it hits home for people like me!
Speed Fuel Cap End Cargo
Ship 1 08 500 2000 100
Ship 2 16 500 2000 100
So, whatever measure we use, Ship 2 should generally be twice as good as Ship 1.
Here are some questions we want to answer:
- How much cargo can we move per day? Speed * Cargo
- How far can we move this cargo without refueling? End * Speed * Cargo
- How efficient is that movement? End * Speed * Cargo / Fuel
Speed Fuel Cap End Cargo Daily Cargo Cargo Efficiency
Ship 1 08 500 2000 100 800 1600000 3200
Ship 2 16 500 2000 100 1600 3200000 6400
So in this case, the efficiency measure shows Ship 1 is twice as good as Ship 2. Doubling/Halving any of the other parameters should essentially show the same thing. i.e., if Ship 2 has End of 1000, it will have an eff of 3200, same as Ship 1. Double Ship 1's cargo will make up for the speed, etc.
It is important to note that this only makes sense under the constraints. In other words, if you don't move the full endurance, the effiency is not accurate, you'd have to substitute the actual Endurance of the trip if shorter.
< Message edited by Graymane -- 10/28/2011 2:11:04 PM >