REFUELLING ASSIGNMENT ONE NAME:

These assignments assess your practical understanding of the content of the Workbook

A. Calculating Vessel Range

When you are calculating how far your vessel can travel on full fuel tanks, ensure that any intended voyage is significantly shorter than your vessel’s maximum range. This will leave an amount of fuel in reserve as a safety measure.

This safeguard will compensate for increases in your vessel’s fuel consumption due to heavy weather, accidents or deviations to the intended course. Typically a reserve of 20% is regarded as a minimum against running out of fuel.

Depending upon the size of your vessel and its engine/s, it will have a standard fuel consumption rate, expressed in litres consumed per hour of operation when running at a set speed. This consumption rate will not take into account any factors which may increase fuel consumption (such as rough conditions or poor engine performance) and should be used as a guide only.

As you know your vessel’s fuel consumption and its fuel capacity, you will be able to calculate the vessel’s range.

First, you should be aware of the standard maritime measurements.

1 nautical mile (nm) = 1.852 kilometres

1 knot = 1 nautical mile per hour

Example

If your vessel has a fuel consumption of 12 litres/hour at 7 knots and a fuel capacity of 250 litres - calculate how far your vessel could travel.

Step 1

Calculate how many hours your vessel could run on its fuel capacity.

Time = fuel capacity

fuel consumption

= 250/12

= 20.8 hours

Step 2 Using the formula

Change this formula to:

Distance = Speed x Time

= 7 knots x 20.8 hours (from above info.)

= 145.6 nautical miles

Your vessel could travel 145.6 nautical miles

Written Activity

A vessel has a fuel consumption of 14 litres an hour at 8 knots and a fuel capacity of 300 litres.

(a) How many hours can this vessel run considering its capacity?

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(b) How far can this vessel travel?

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Check your answers at the end of this section.

B. Calculating Fuel Requirements

It is crucial to ensure that your vessel always carries more fuel than is necessary to undertake a particular voyage.

Whilst there are many factors which make it difficult to accurately determine how much fuel your vessel will use, there are basic calculations which can be used as a minimum guide.

The amount of fuel your vessel will require is equal to the fuel consumption multiplied by the time travelled.

Example

If your vessel has a fuel consumption of 6 litres/hour at 5 knots and a voyage will take 8 hours, calculate the amount of fuel your vessel will require:

Fuel required = fuel consumption X time

= 6 x 8

= 48 litres

Your vessel will consume 48 litres of fuel

Written Activity

Try these calculations:

1 If a vessel has a fuel consumption of 8 litres an hour at 6 knots, and a voyage will take 8 hours, calculate the amount of fuel your vessel will require:

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2 If a vessel has a fuel consumption of 10 litres an hour at 9 knots, and a voyage will take 4 hours, calculate the amount of fuel your vessel will require:

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Check your answers at the end of this section.

C. Calculate Fuel Tank Capacity

Fuel tanks come in all shapes and sizes depending upon the vessel design and available space. Normally, the fuel tank manufacturer will advise the tank’s capacity, either as cubic metres or in litres.

1 cubic metre = 1000 litres

To calculate the capacity or volume of a simple rectangular fuel tank follow these steps:

Step 1

Measure in metres, the tank’s external size:

Length (L)

Width (W)

Depth (D)

Step 2

To accurately calculate the volume of the tank, you will need to use the internal measurements of the tank.

Simply subtract the thickness of the tank material from each measurement. You will need to do this twice to account for each side.

E.g. Length - (thickness x 2)

Width - (thickness x 2)

Depth - (thickness x 2)

Step 3

Volume = Length x Width x Depth

Follow this formula to calculate the volume in cubic metres:

Step 4

To calculate the volume in litres, multiply the answer in Step 3 x 1000.

Example

If a fuel tank on your vessel has external measurements of length 2.5 metres, width of 1.25 metres, depth of 1.0 metres and is 0.025 metres thick, calculate the volume in litres.

Step 1

External Measurements

L = 2.5 m

W = 1.25 m

D = 1.00 m

Step 2

Internal Measurements

L = 2.5 - (0.025 x 2) = 2.45

W = 1.25 - (0.025 x 2) = 1.20

D = 1.00 - (0.025 x 2) = 0.95

Step 3

V = L x W x D

= 2.45 x 1.20 x 0.95

= 2.79 cubic metres

Step 4

V = 2.79 x 1000

V = 2790 litres

The volume of the fuel tank is 2790 litres.

Written Activity

1 A vessel has a fuel tank with internal dimensions of:

H = 4.30 m, W = 4.30 m and D = 1.30 m

Calculate the tank’s capacity in cubic metres and in litres.

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2 Can you accurately measure a fuel tank’s capacity if you are advised of the length, width and depth? What other information, if any, do you require?

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D. Calibration of Fuel Tanks

Due to the motion of a vessel, fuel tank capacity cannot be accurately measured by the installation of a fuel gauge. Additionally, in smaller vessels the tank may be constructed in an irregular shape to optimise space. The consequence will be that the rate that the level of the fuel lowers will not be constant.

It is therefore important that any other measure of the fuel levels must be undertaken when the vessel is on an even keel and the tank or the measuring device is calibrated to match its irregularities.

Common methods employed are by use of a Sounding rod, an Ullage stick or a Sight glass.

The sounding rod measures the changing depth of the fuel in the tank.

The ullage stick measures the unfilled depth in the tank above the fuel level.

The sight glass duplicates the height the fuel by running an external transparent pipe from top to bottom of the tank.

Written Activity

1 Describe a method you could use to accurately calibrate a sounding rod on a new vessel that takes into account an irregularly shaped tank.

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2 Explain why measuring an ullage (as opposed to a sounding) is required by the tanks of some vessels.

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3 Explain why it is important to open the self closing valve on the bottom of a sight glass before taking a reading. Why is such a valve a survey requirement.

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Check Your Progress

1 What is reserve fuel and why do you carry it?

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2 Calculate how far a vessel could travel if fuel consumption is 13 litres an hour at 9 knots and a fuel capacity of 280 litres:

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3 A vessel has a fuel consumption of 5 litres an hour at 6 knots. A voyage will take 2 hours. How much will this vessel require as a minimum, allowing for a safe reserve?

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4 1 cubic metre =__________ litres.

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