A ship without a crew is simply a large, expensive metal assembly; a ship with an incomplete or incom­petent crew is, in the eyes of the law, unseaworthy.  These somewhat self evident points are made to remind you that the crew is a vitally important element in a trading ship.  Whether one is directly involved in crew matters or simply has to communicate with a ship from time to time, a knowledge of the human con­stituent in a working ship is essential. The size of a ship’s company of officers and ratings will, of course, vary in the first instance according to the size of the ship but other factors can in­fluence the numbers.  The complexity of the ship will have an effect as will the flag.  The latter because different countries have different laws about manning which have come about by a combination of their views on safety and the insistence of labour unions. Regardless of size however there is a basic pattern common to all ships in that there must first be a Master – the ship’s Captain – the man in overall charge.  Assisting him will be the First Officer, who has a traditional range of very important duties of his own as well as being the Captain’s deputy.  Beneath him will be the second, third, fourth mate etc, the number being dictated by the ship’s size but the minimum will always have to be enough to have at least one suitably qualified navigating officer on watch at all times. Operating as a separate department are the engineers presided over by the Chief Engineer.  His complement of officers will not only be dictated by size and national agreement but also by the sophis­tication of the engine room.  Modern ships are so carefully monitored by electronic devices that the Chief Engineer can work normal office hours and lock up the engine room at night, leaving computerised sensors to set off alarms to wake him if an emergency occurs.  Some ships carry an electrician in addition to the other engineering staff.