From: Brussels, Belgium
Every Oil point you bring to Oz will need to be processed through the 55 Refineries (if I remember correctly the numbers in Scen 1). I think you also have 10 Oil centers, so only 45 Refineries will work on imported Oil (or 450 Oil points processed per day). If you bring more than that each turn (on average), it’s wasted - well, not really wasted but useless. And the daily process will give you 45 Supply and 405 Fuel, which may then be used to fuel 202.5 HI, ending up as 405 Supply. So, bringing Oil gives 450 Supply per day.
However, there’s around a 1000 HI (a bit over that, but not much), which requires over 2000 Fuel to work. So, you still have to bring four or five times as much Fuel as Oil.
End of day, if you bring enough Oil to make the Refineries work every day, you end up needing to bring an additional 45 liquid cargo per day (over a requirement of a bit over 2000, that’s not much), while the benefit is 45 additional Supply (not much compared to the 2000 you get from HI). So, if you’re okay with an additional piece of paperwork, just to have the equivalent of a additional cargo ship full of Supply every four months...
And the calculations for benefit should also account for any fuel burned by the ships bringing in the oil/fuel if they refuel in Oz. Most of the tanker traffic coming from the US or Abadan must take on a small amount of fuel to get back to their home port. To obviate that, I set a refueling waypoint for the tanker to take on enough fuel to get to Oz and back to home base (set refueling amount to "minimum").
Indeed, but in the end it’s beneficial to bring Fuel with tankers (if you haven’t lost too many) rather than the same amount of Supply, if looking from a Fuel efficiency for the transport POV.
Running the numbers from memory, here, so details are a little bit different.
Round-trip from West Coast to Oz, by doing a small detour to keep south of the Penrhyn-Pago-Noumea line, is 360 hexes. A T2 Tanker can only do 315 hexes, so it needs to refuel partly somewhere. Setting a way-station around Pago Pago or Suva would allow the final leg to Sydney and return to the way-station without refueling in Australia.
A T2 needs around 1450 Fuel to get max endurance, so it would need around 1800 for the whole round-trip, and can ship 14000 Fuel, and so can give Oz’s HI the needed Fuel for a week. The round-trip takes two months, so you need 8 T2 to reach Sydney to have enough for the industry. As long as you include a ninth tanker which detachs and unloads in the gas station to replenish the used Fuel, while the rest of the convoy continues, you’re fine. More than fine, in fact, as the T2 refueling the gas station brings more Fuel than needed by the whole convoy (barring a very heavy escort) to safely return home with a tactical refueling.
9 T2 filled at Los Angeles with 14000 Fuel each : 126k Fuel, 112k of which is used by the industry to make as much Supply. Fuel usage for the whole convoy for the trip : 9*1800 = 16,200 Fuel (counting the Fuel used in WC to refill them).
With a Liberty cargo, you have a bigger Endurance, so you don’t need a refueling station, but you only carry 6250 Supply - so you need 18 ships to bring the same quantity of Supply. For the full Endurance, slightly over 400, you need 1800 Fuel, or approximately the same as a T2 - but you need twice as many ships. Given the slight reserve of Fuel the Liberty would have on the return trip (if it has refueled an escort, for example), you can easily consider a use of at least 1700 Fuel for the round trip. 1700*18 ships = 30,600 Fuel.
So, the net result of shipping Fuel with 9 big tankers will be the same, Supply-wise, than using twice as many Liberty ships, but for nearly half the usage of Fuel for the shipping.
That said, as soon as you can get your hands on DEI Fuel, it’s way better to ship it from there. And, from memory, the Cape-Perth round-trip is shorter I think, so if you have too much Fuel there, it’s better than shipping from California. Unless your opponent intercepts the convoys in the Indian Ocean.