Portcities Southampton
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Why are ships so diverse?

Specialisation begins

With early boats it is often difficult to tell in what way they were used.  As they are basically simple, they could have been used equally well for carrying trade goods, for fishing, or simply as a means of ferrying people across a river.  As construction became more sophisticated, specialisation began.  For instance, a warship is designed to be fast and manoeuvrable but to achieve this safety is compromised and space and comfort for the crew is sacrificed.  For a merchant ship, in contrast, cargo capacity and safety may be more important than speed.

Different jobs, different ships

The type of cargo carried is one of the most important influences on the design of a merchant ship.  An extreme example is a liquid cargo like oil, which needs tanks in the hull which are very different from the holds for solid cargoes like coal.  Even with solid or ‘dry’ cargoes, however, there can be differences in facilities needed.  A ship carrying frozen meat will need holds with refrigeration equipment to keep the cargo below zero.  A banana ship, in contrast, just needs to keep its cargo well ventilated but not frozen.

The amount of cargo available and the size of ports served also strongly affect the design of a ship.  For instance, a coastal tanker running between an oil refinery and a distribution depot in a minor port will not only be much smaller than a ultra-large crude carrier (ULCC) carrying crude oil from the Arabian Gulf, it will also have tanks of varying sizes to segregate different types of petrol, diesel and other products.

With a fishing vessel, the type of fish caught affects its design.  A distant-waters trawler regularly fishing for cod in arctic waters will be bigger and more strongly built than a seine-netter catching herring or mackerel in inshore waters.  The trawler will have facilities to freeze or even process its catch to keep it in good condition for the long voyage home, whereas the smaller vessel does not need these facilities.

With ships designed for specialised jobs, such as suction dredging, carrying heavy cargo, or conveying nuclear fuel, the particular needs of that job will obviously influence the form of the ship.