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| UNDERSTANDING ENGINE EFFICIENCY | |
| Around 70% of a ship’s energy consumption comes from the engine’s operation. It is quite significant that, in most part, the engine supplies the propelling force that moves a ship; being this a reason why it is extremely important their adequate operation and preservation – representing one of the most extensive opportunity fields in savings – which means minor costs and higher efficiency. |
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These savings start from the appropriate motor selection. We can always find an equipment that meets all our requirements, either for its operating conditions as well as for their size or power. Higher savings are obtained once the engine and its load are operating at its maximum efficiency.
The efficiency or yield of a motor is a measurement of its ability to turn the electrical power that takes from the line in useful mechanical power. It are usually expressed in a percentage of the relation of the mechanical power between the electrical power, this is:
Not all the electrical energy that a motor receives becomes mechanical energy. In the conversion process, losses appear, reason why the efficiency never will be of the 100%. If the conditions of operation of a motor are incorrect or this it has some flaw, the magnitude of the losses, can surpass with much those of design, with the consequent diminution of the efficiency.
For calculating efficiency, the power units must be equal. Due that the mechanical power is usually expressed in HP, the propulsion power will also has to be in HP.
In most cases, the marine engine power is expressed in KW, so, we will use the following equivalents for unit conversion:
1 HP0.746 kW
1 kW
On a ship, power losses of the main engines are mainly caused by:
- Friction on the propelling shafts with their bearings, which go from 4 to 6% .
- Water displacement friction, for which the ship must have good line forms designs so they can help reduce losses for this concept.
- Obstacles found in the water flow, such as wrong designed stabilizers, propeller protection structures, external refrigerating (cooling) systems at the hull, etc.
When we add up all these losses and deduct them from the engine power, the efficiency can be found in a percentage according to the above expressed formula.
By the previously expressed, there are several ways of loss that decreases efficiency, and as long as we can minimize them, we will be contributing to our engine’s good performance.
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