Why hulls had to leave the water
A wooden ship is attacked from below. Marine worms bore into planking, weed and shellfish foul the bottom and slow the vessel, and seams open with age. Any ship in regular service therefore needed to be examined and repaired below the waterline, and a new ship needed a place where its hull could be assembled on a stable base. Both needs led to structures that brought the vessel out of the water, or kept the water out of the vessel’s surroundings.
Boat builders had a range of simple methods. Small craft could be hauled up a beach, turned over on shore or supported on props between tides. This is called careening when a vessel is deliberately laid over on its side, and it remained common for repairs on remote coasts long after more elaborate structures existed. Larger ships, and navies with many of them, needed something more permanent.
Slipways and ship sheds
The simplest permanent structure is the slipway, an inclined surface running down into the water. A vessel is built on it, supported by timbers, and then slides down when released. Ancient Mediterranean cities built long roofed sheds with sloping floors in which warships could be kept ashore. Archaeological work at Piraeus, the port of Athens, has identified rows of such sheds, and similar arrangements are described for the Phoenician and Carthaginian naval harbours. The important point is that keeping a light oared warship out of the water preserved its timber and kept it ready for use.
Later shipyards built slipways that were uncovered or sometimes roofed against the weather. Over the centuries the technique of launching changed little in principle: the ship was built on blocks, the hull was braced, the supports were removed, and the ship moved into the water under its own weight on greased timbers. Launching a large vessel was a spectacle, and also a moment of real risk to the hull.
The graving dock
A graving dock, or dry dock, is a basin that can be emptied of water. A ship floats in at high water or when the basin is full, the entrance is closed by gates or a caisson, and the water is drained so that the ship settles on blocks. Workers can then reach the whole hull.
The graving dock is much older than the modern industrial yard. Tradition holds that a dock at Portsmouth was built in the reign of Henry VII, in the 1490s, and that this was an early dry dock for the English navy, though details of the original structure are limited. By the seventeenth and eighteenth centuries the major naval powers had stone or timber docks at their principal yards. In Britain these were part of the system described in the article on the royal dockyards.
Emptying a dock took considerable effort. Where the tide fell far enough, a dock could be drained by opening a sluice at low water, but a full drain often required pumps. Horse-driven and later steam-driven pumps made it practical to empty ever larger docks quickly, which in turn shortened the time a ship spent out of service.
The patent slip
One notable nineteenth-century development was the patent slip, a cradle running on rails up an inclined slope. A ship was floated over the cradle, secured and hauled out by machinery. A design of this kind, patented in 1818 by Thomas Morton at Leith in Scotland, made it possible to haul out vessels at much lower cost than a masonry dock. Variants spread through British ports and overseas colonial harbours, and slipways of this type served fishing boats, coasters and small steamers well into the twentieth century.
Floating docks and iron
As ships grew, the cost of masonry docks grew with them. The floating dock offered an alternative: a large hollow structure that could be flooded to sink it, then pumped out to lift the ship above the water. Floating docks were portable in principle, and could be towed to where they were needed, which suited naval bases and ports without enough land for a permanent basin.
The development of iron shipbuilding in the nineteenth century increased both the size of vessels and the demands made on repair facilities. Iron hulls corroded and fouled, and the large steamships of the steamship era required docks of greater length, breadth and depth. Victorian engineers built granite-lined graving docks of impressive size, with stepped sides called altars, pumping stations and gates large enough to close a channel many metres wide. Port cities competed for the repair trade, which supplied steady work and revenue.
Modern graving and building docks
In the twentieth century, shipyards increasingly built vessels in dry docks rather than on inclined slips. Building a hull in a dock, which is then flooded for the ship to float out, avoids the risks of a traditional launch and suits very large vessels such as tankers. Welded construction and prefabricated blocks, assembled and moved by heavy cranes, further changed how docks were used. Many shipyards combine building and repair, with large docks serving whichever work is on hand.
Surviving examples
Historic dry docks have a second life as heritage. HMS Victory has been kept in a dry dock at Portsmouth since the 1920s, supported on blocks and shores, and the clipper Cutty Sark is displayed in a dry berth at Greenwich. Many historic docks elsewhere have been converted into museums, marinas or event spaces, and their granite walls, steps and pump houses still show how ships were once brought out of the water for work. For historians, the structures themselves are evidence of the size of ships a port could handle and the importance it gave to repair.