Plan Refueling or Fuel Transfer Operation | Fuel Calculations |
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Calculating the Volume of a Fuel Tank
See below the formulas for calculating the Volume of Fuel Tanks for varying shapes. |
| Trapezoidal Tank | Volume = Length x (Width at the top + Width at the bottom/2 x Height | |
| Cylindrical Tank | Volume = Length x 3.1416 x Radius x Radius | |
| Triangular Tank | Volume = Length x Width x Height/2 | |
| More Complex Shapes | "Break the shape down" into sections with simpler, more regular shapes, then use the above formulae. |
Calculating the Weight of Fuel
It is important to take into account the weight of the fuel in the tanks when balancing the load around the vessel. If a calculation can be made of how many litres of fuel is onboard and the weight of one litre of fuel is known the total weight of the fuel load can be calculated.
Specific Gravity is defined as the ratio of the density of a solid or liquid substance to that of plain water. The weight of a substance can be calculated with the following formula: Weight of Liquid Substance = Volume of Liquid Substance x Specific Gravity of Substance |
Specific Gravity can be used to workout whether items will sink or float in water. If the value is less then 1 the solid or liquid substance will float in water and if it is higher that 1 it will sink in water.
As 1 Litre of plain water weighs 1 Kilogram, specific gravity can also be used to convert a known volume of a solid or liquid substance to a weight in Kilograms.
If a fuel tank can hold 3000 litres and is full to 90% capacity and you know the specific gravity of the fuel is 0.86. The weight of the fuel can be calculated as follows:
Weight of Liquid Substance = Volume of Liquid Substance x Specific Gravity of Substance
Weight of Liquid Substance = (3000x0.90) x 0.86
Weight of Liquid Substance = 2322 Kg
Fuel Consumption Calculations
If the rate of fuel consumption remains steady* for a certain steaming speed then calculations can be made to work out the distance that can be travelled before a certain amount of fuel is used or the amount of fuel used after travelling a certain distance.
Calculating Distance Travelled
If a vessel is steady* steaming at 15 knots and records show that with steady steaming the average consumption of the ship is 85 litres per hour. Ignoring weather, how far can you steam at this speed before the tank is 25% full?
Initially the Fuel Level is at 90% and will be reduced to 25%.
Fuel Consumed = 3000 x (0.90 - 0.25) = 1950 Litres
Time taken to Consume Fuel = Amount of Fuel/Consumption Rate = 1950/85 = 23 hours
Distance Travelled in the time taken to Consume Fuel = 23 hours x 15 knots = 345 Nautical Miles
Calculating Remaining Fuel
If a vessel is steady* steaming at 15 knots and records show that with steady* steaming the average consumption of the ship is 85 litres per hour. Ignoring weather, if you steam 120 nautical miles at this speed, how much fuel will remain in the tank?
Initially the Fuel Level is at 90%
Time taken to Consume Fuel = Distance Travelled/Speed = 120/15 = 8 hours
Fuel Consumed = Time Travelled x Consumption Rate= 8 x 85 = 680 Litres
Remaining Fuel in Tank = (3000 x 0.90) - 680 = 2020 Litres
Capacity Remaining in Tank = Fuel Left / Tank Capacity = 2020/3000 = 67%
Using the dimenstions of Tank A and Tank B pictured. Answer the questions given for each tank. |
- How many litres of fuel are in the tank when it is at 95% capacity?
- Given a specific gravity of 0.86 for diesel fuel, what do the tank contents weigh?
- If a vessel is steady* steaming at 12 knots and records show that with steady* steaming the average consumption of the ship is 65 litres per hour. Ignoring weather, if the tank at 95% capacity, how far can you steam at this speed before the tank is 25% full?
- If a vessel is steady* steaming at 12 knots and records show that with steady* steaming the average consumption of the ship is 65 litres per hour. Ignoring weather, if the tank is at 95% capacity and you steam 240 nautical miles at this speed, how much fuel will remain in the tank?
Download the questions in a handout by clicking here.
Once you have completed the activity, check your answers by clicking here.
* Wind and tide have been taken out of the equation.
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