A collier is a bulk cargo ship designed to carry coal, especially for naval use by coal-fired warships. In the late eighteenth century, a number of wooden-hulled sailing colliers gained fame after being adapted for use in voyages of exploration in the South Pacific, for which their flat-bottomed hulls and sturdy construction made them well-suited. The first aircraft carrier in the United States Navy was a converted Collier, fitted with a large elevated flat deck, used before the invention of purpose-built aircraft carrier hulls. Coaling at sea was critical to navies and speed of coal transfer was an important metric of naval efficiency. In 1883, forty tons an hour was considered fast and it would take over twelve hours to restock half the bunkers of a typical ship, HMS Collingwood (1882). For many years, the Durham and Northumberland coalfields supplied the rapidly expanding London with vast tonnages of coal, and a large fleet of coastal colliers travelled up and down the east coast of England loaded with "black diamonds". Sir Charles Palmer pioneered the construction of iron-hulled steam colliers at his Jarrow shipyard, which began to rapidly replace the earlier wooden ships. This inadvertently led to the eventual decline of the glassmaking industry on Tyneside and Wearside, as prior to this, they had had access to large supplies of sand, used as ballast in the wooden colliers returning from London. The iron colliers had ballast tanks which meant water could simply be pumped in, greatly reducing the turnaround time as the sand no longer needed to be loaded and unloaded. Coal was also exported to Europe, and wooden colliers returned with goods such as roofing tiles in their holds. The first Palmer-built iron hulled steam collier was the SS John Bowes of 1852. There had been an earlier iron hull screw propelled collier, the short-lived SS Bedlington of 1841 built in South Shields. A notable incident involving a collier occurred not long after the opening of the Victoria Tunnel in Newcastle. The hemp rope which controlled the speed of wagons descending the tunnel to the river from Spital Tongues Colliery snapped, and the wagons landed in the Tyne. This time, the wagons were recovered at low tide, the rope was repaired, and the papers of the day treated the whole incident as something of a joke. Six months later, the rope snapped again, and the wagons landed in the hold of a waiting collier and sank it. After this, it was decided a wire rope would be a better option. This is probably the only recorded incident of a train having sunk a ship. Loading and unloading Loading the colliers was carried out by hand at first, especially where coal was transferred from keels which had brought it downstream from parts of the river that the colliers were unable to navigate, but as the quantities handled increased, specialised jetties known as "staithes" began to be built. These were of numerous designs. Some had spouts used for unscreened or small coal, others known as "drops" had steep inclines at the end, down which a wagon would be lowered directly into the hold, minimising the breakage of coal. Some had both drops and spouts. The drops and spouts could be raised and lowered with the tide. Later, elevators began to be introduced, such as those at Bates Staithes in Blyth, Northumberland and Harton Low Staithes in South Shields. These staithes used spouts. The largely intact Dunston Staithes on the Tyne are a good example of this type. In Scotland, a system was common where wagons would be placed on a cradle and lifted into the hold of the ship, but this system was rarely used elsewhere. Two large steam cranes were built for this purpose at the Harton Low Staithes, but it was found that despite their size and power they were too slow to handle the amount of coal that was arriving at the staithes, and were replaced by elevators. The men who worked at the staithes were known as teemers and trimmers. Teemers would open the doors on the bottom of the wagons to allow the coal to fall into hoppers under the rail deck on top of the staithes, or in the case of drops, directly into the hold of the collier. The trimmers worked in the hold, spreading and levelling the coal with shovels and rakes so that its weight would be evenly distributed. Skilled trimmers could stand with their shovel under the stream of coal coming from a spout or the end of a conveyor and angle it so the coal would ricochet off into the part of the hold they wanted to fill. This was a dangerous job, as the holds could fill with firedamp given off by the coal, resulting in an explosion. More modern systems are designed to be able to evenly distribute the coal without the need for men working in the holds of the ships. Although, in later years, the colliers faced competition from the railways in supplying coal for domestic use in the capital, large quantities of coal were used at the numerous power stations on the banks of the River Thames, and wharves were constructed alongside them for unloading the colliers. The wharf at Battersea Power Station is still extant, and the cranes used for unloading the coal can be seen on the riverfront. These are fitted with clamshell buckets and in operation loaded a hopper, which in turn fed a conveyor system leading to the power station's coal bunkers. The modern equivalent can be seen at the Tyne Coal Terminal, unloading bulk carriers. Gas Light and Coke Company had similar facilities at its large gasworks, also alongside the Thames, for handling the large quantity of bituminous coal which was needed to supply the capital with town gas.