Convoy Fuel Planning: Two Legs, One Reserve Rule
A convoy of 12 vehicles must move 180 km from Camp A to a forward location. Eight vehicles are laden and burn 0.35 litres per km; four are unladen and burn 0.28 litres per km. The fuel truck carries 1,200 litres of usable diesel after its own running needs are set aside. Standing instruction: at the end of the move, fuel remaining must be at least 10 per cent of the fuel consumed on the whole move. The bridge on the direct route is closed for the return, so the return leg is 210 km, with all 12 vehicles unladen.
1. Calculate the fuel required for the outbound leg, including the reserve, and state the surplus or deficit against the 1,200 litres carried.
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Outbound consumption
- Laden: 8 vehicles x 180 km x 0.35 L/km = 8 x 63 = 504 L
- Unladen: 4 vehicles x 180 km x 0.28 L/km = 4 x 50.4 = 201.6 L
- Total consumed: 705.6 L
Reserve: 10 per cent of 705.6 = 70.56 L
Requirement: 705.6 + 70.56 = 776.16 L
Against 1,200 L carried: surplus of 1,200 - 776.16 = 423.84 L.
The outbound leg alone is comfortably within the fuel held. Note that the surplus is not spare capacity for the whole move - it is what the return leg must be planned against.
2. Now plan the whole two-leg move. Is 1,200 litres sufficient? If not, how many 20-litre jerricans must be loaded?
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Return leg consumption
All 12 vehicles unladen: 12 x 210 km x 0.28 L/km = 12 x 58.8 = 705.6 L
Whole-move consumption: 705.6 (out) + 705.6 (return) = 1,411.2 L Reserve (10 per cent of consumption): 141.12 L Total requirement: 1,411.2 + 141.12 = 1,552.32 L
Deficit: 1,552.32 - 1,200 = 352.32 L
Jerricans: 352.32 / 20 = 17.62 - round up, since a part-full jerrican still has to be carried. 18 jerricans (360 L) are required, leaving 7.68 L of margin over the minimum.
Rounding down to 17 would leave a shortfall of 12.32 L and breach the reserve rule.
3. A refuelling point on the return route, 120 km from the forward location, can issue 300 litres. How many jerricans are now needed? State any assumption your answer depends on.
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Revised fuel available: 1,200 + 300 = 1,500 L
Requirement (unchanged): 1,552.32 L
Deficit: 1,552.32 - 1,500 = 52.32 L
Jerricans: 52.32 / 20 = 2.62 - round up to 3 jerricans (60 L).
Assumption: the 300 litres is physically available and issued when the convoy reaches the 120 km point, and the refuelling stop does not itself consume time or fuel beyond the figures given. It is also worth checking the vehicles can actually reach that point: consumption over the first 120 km of the return leg is 12 x 120 x 0.28 = 403.2 L, which is well inside what the vehicles carry, so the plan is feasible rather than merely arithmetic.