Calculating fuel and water

Fuel and Water Math for Desert Crossings

In the desert, your "range" is not a suggestion; it is a hard limit. Use these formulas to calculate your requirements before you leave the last outpost of civilization.

1. Fuel Range Calculation

Standard "highway" fuel economy (MPG or L/100km) is irrelevant once you hit soft sand, high heat, and low-range gears.

• The "Off-Road Factor": As a rule of thumb, assume your fuel consumption will increase by 50% to 100% in deep sand or technical terrain.
• The Formula (Metric):
  • Total Fuel Required = (Distance x (worst case) fuel consumption L/100km) x 1.25
  • Note: The 1.25 multiplier adds a mandatory 25% safety reserve for backtracking, idling, or getting bogged.

• The Formula (Imperial):
  • Total Fuel Required = (Distance / (worst case) fuel consumption MPG) x 1.25

Example (Simpson Desert Style):

If the track is 500km and your vehicle usually gets 10L/100km (Land Rover 2.2Tcdi):

1. Adjust for terrain: Use a "Worst Case" of 15L/100km.
2. Calculate base: 500 x (15/100) = 75 Liters
3. Add 25% Reserve: 75L x 1.25 = 93.75 Liters
4. Final Result: You must carry ~100L of fuel.

2. Water Requirements

Water is heavy (1 Liter = 1 Kilogram), so while you want plenty, you must also manage vehicle weight.

• The Daily Ration:
  • Survival Minimum: 3-4 Liters per person/day (Drinking only).
  • Overland Standard: 7-10 Liters per person/day (Drinking, cooking, basic hygiene).
• The Formula:
  • Total Water = (People x Days x 10L) + 20L (Emergency Reserve)

Example:

Two people on a 5-day desert crossing:

1. Base: 2 people x 5 days x 10L = 100L.
2. Reserve: Add 20L for a breakdown/delay.
3. Total: 120 Liters.

3. Crucial Desert Rules

• The "Point of No Return": Calculate your "Half-Fuel" mark. If you reach the halfway point of your fuel and you have not reached the halfway point of your distance, you must turn back immediately.
• Check the "Usable" Capacity: Many fuel tanks cannot suck up the last 5-10 liters due to the shape of the tank or fuel slosh. Never count the last 10% of your tank as "usable."
• Separate Your Water: Never keep all your water in one large tank. If the tank springs a leak or the pump fails, you lose everything. Distribute water across a main tank and at least two 20L jerry cans.
• The "Sip" Method: If you become stranded, do not ration water to the point of dehydration. "Water in the belly is better than water in the bottle." Drink when thirsty to keep your brain functioning for problem-solving.

Item	Weight (Approx)	Storage Tip
Diesel/Petrol	0.85 kg / Liter	Keep weight low and centered.
Water	1.00 kg / Liter	Store in food-grade, opaque containers to prevent algae.