Electrical cables: how to design an electrical system on a ship

Designing an electrical system inside a ship is no small feat. We certainly need consolidated experience, to make the right choice of components and we need to rely on a system that must ensure the continuity of the power supply for the electrical equipment, or at least for the basic equipment that is necessary for the safe maintenance of the ship.

The criticality of an electrical system on a ship:

What complicates the construction of an electrical system on a ship, are, first of all, the characteristics of the ship itself. Primarily, we are talking about an isolated system, so if the power supply is suddenly stopped, it is impossible to rely on other support networks. Moreover, when the large engines on which the network depends are lighted up, they create such voltage fluctuations that the entire system becomes vulnerable.  

Moreover, the space inside a ship is small and the weight of all the equipment that will be used to make it, cannot exceed a certain weight.
Even environmental and weather conditions, such constant humidity and very high or very low temperatures, depending on the season, to which it is subject, can represent a danger for the electrical components since they are very fragile. Finally, a ship is a mobile vehicle: its movement inevitably subjects the system to strong stresses and vibrations. For all these reasons, the electrical system on a ship must be built carefully.

Here you will find the characteristics that an electrical system on a ship must have:

In order to deal with the problems listed above, an efficient electrical system must necessarily have special characteristics that make it stable and safe even in the most extreme and difficult situations.
The weight and size of the equipment must be kept to a minimum and it is very important that it adapts to the shape of the ship itself. Dismantling and maintenance must be simple and allow adequate manoeuvrability. Of course, each component must have a high degree of resistance to the corrosive and deleterious action of sea air and salt water and minimize the risk of fire on board. The material used when building a system must, therefore, be robust and suitable for the particular conditions of a sailing boat. Moreover, in addition to the appropriate choice of components, it is necessary to adapt certain system solutions to ensure continuous power supply.

An electrical system is essential on a ship because it doesn’t not only assure the comfort of the passengers but also and above all, the safety and the navigation of the boat depend on it.  It powers all vital equipment such as the radar, the depth sounder, the compass, and the sonar, as well as all the other equipment, from lighting to air conditioning and entertainment for the passengers of the ship.

The system is divided into three main sections: the main system, the special systems, and the auxiliary circuits.
First of all, it is necessary to establish the amount of electrical power that the ship will need. This figure is nothing more than the full power required by the sum of all the electrical systems to be calculated in all possible arrangements of the ship: at sea, at anchor and so on. Such power must of course guarantee the simultaneous operation of all this equipment even in the most unfavourable and severe conditions; even in the unfortunate and remote hypothesis that an alternator is lost.
The choice of the size and of the total number of Diesel units must, therefore, be made in relation to all these conditions. Once the value of the total onboard power has been defined, it is necessary to determine a second parameter which corresponds to the mains voltage. Naturally, as electrical power increases, the operating voltage must also be increased.

Always during the design stage, it is important to compile a detailed list of all the utilities on board and indicate, for each utility, the number of machines that will use them and the power that will be absorbed. The utilities will then be divided into different categories, such as safety (navigation, emergency, stabilization, fire, radio), deck (rudder, tonnage, winches), loading (hoists, boilers and refrigerators), air conditioning (boilers, refrigerators, air conditioners), kitchen (bars and refrigerators), light (internal, external, normal, emergency) and so on.

Once the list has been established, it is possible, for each individual category to define the power consumed. The power consumed can also be calculated according to the different hours of the day and this will allow having a complete and precise picture of the so-called electrical balance.
The shipping registers, which certify that the ship was built according to the right criteria and in compliance with the regulations, require the presence of an independent source of energy from the main switch that can act as an emergency power station in case of need and that is able to function even if the main network does not provide energy.

The difference in design between onshore and onboard systems

What is essential while designing an electrical system for onboard use is that it must follow the specific techniques required by the situation. It is therefore recommended not to adapt onshore systems to the nautical industry since the two dimensions are very different.  

Common onshore power grid failures can cause dangerous damage to a ship. In order to guarantee a maximum safety, it is essential to use non-toxic cables, prepare an adequate fire-fighting system, duplicate the power supply line and take care of many other precautions that would not be necessary in normal onshore based systems, that do not work under extreme conditions such as those of a ship generator.
Thanks to the great development of electronic equipment, electricity has reached an increasingly important and relevant value. These great developments need to be absolutely adapted to the construction of a system that ensures stability and above all security.

Leave a Reply