Usually electrical systems ashore are seldom operated at constant load, day and night and also for long periods. In the shore-based industry there are peak loads and off-peak loads; these factors have considerable effect on the life of equipment. They also may be re-modelled as new production lines and concepts are introduced or new machine tools become available. But this is not the case in the marine industry. Electrical equipment is expected to last the lifetime of the installation and of die vessel too in most cases. During this time, maximum reliability is important, particularly with regard to those services which are vital for propulsion and safety of both the ship and personnel.
Effects of Inclination
With reference to SOLAS Chapter II -1 – Part C – Machinery Installations – Regulation 26 – paragraph 6, ‘Main propulsion and all auxiliary machinery essential to the ship shall, as fitted in the ship, be designed to operate when the ship is upright and when inclined at any angle of list up to and including 15° either way under static conditions and 22.5° under dynamic conditions (rolling) either way and when simultaneously inclined dynamically (pitching) 7.5° by bow or stem. The Administration may permit deviation from these angles, taking into consideration the type, size and service conditions of the ship’.
In addition to the above regulation, SOLAS Regulation Chapter II-1, Part D, Regulation 42, paragraph 6, states that ‘The emergency generator and its prime mover and any emergency accumulator battery shall be so designed and arranged as to ensure that they will function at full rated power when the ship is upright and when inclined at any angle of list up to 22.5° or when inclined up to 10° either in the fore or aft direction or is in any combination of angles within those limits’ .
One of the main factors concerned with these inclinations is that of lubrication and another is that of the functioning of the contactors, switchgear and relays having unsymmetrical or unbalanced magnet systems, where the magnetic pull (to operate them) increases with inclination. Any apparatus containing oil, such as transformers or switches and solenoids will also be affected.
