The deposit of mud and silt on the bed of the River Tawe was known as the layer, and it was considered beneficial for any port to have a thick layer of this type of material to allow sailing ships to ground on the river bed at low water without causing damage to the hull. One of the problems encountered with sailing ships was that, without any cargo on board, they were not very stable, and to counteract this problem they would be loaded with large stones as ballast. When they arrived at their berth the ballast would be unloaded and maybe used by another vessel leaving port without cargo. However, it became the practice of many ships to dump this ballast overboard whilst entering the harbour, possibly to reduce the time in port, or perhaps to minimise the draft of the ship so that it could come in on a low tide. Whatever the reason, it was evident from the 1500s that the dropping of ballast, not only at the harbour entrance but also at the wharves within the river itself, was beginning to have a detrimental effect. Ships were damaging their hull timbers by settling on an accumulation of stone rather than on a thick layer of mud at low tide, and a build-up of dumped ballast at the harbour entrance was restricting the size of vessel able to enter the port.
In 1584 the first Layer Keepers, Owen Rees Thomas and Thomas Vichan, were appointed to curtail this activity and to fine any master responsible for the offloading of ballast into the channel. The stones were removed from the river bed (the layer) and from the ‘bar’ at the harbour entrance in what was probably the first operation of its kind, ultimately leading to the regular dredging of excess quantities of mud and silt carried daily downstream by the River Tawe and deposited within the navigable channel of the port.
As ports and harbours such as Swansea developed over the centuries, dredgers of various types were utilised to achieve the greater depths of water needed to accommodate ships of ever-increasing sizes. In the early years vessels known as 'spoon' dredgers would have been used in many locations - each boat being operated by a crew of up to five men manually wielding a large scoop on a long pivoted handle to grab up silt from the bottom of the canal or dock. Another early type of dredger consisted of a barge with a rudimentary bucket system powered by a horse, working on a similar principal to a horse gin.
By the end of the eighteenth century, these little craft were being overtaken by a variety of steam-driven mechanical innovations such as barges mounted with grab cranes, and dredgers with continuous bucket-ladders such as the ‘David Davies’ or the ‘Abertawe’. It is recorded that the first steam dredger was built as early as 1797 for use in Sunderland harbour, and that steam dredgers were used from 1824 to clear the bed of the River Clyde. In fact, it was in the Clydeside ship-building yards of Glasgow that many of these early steam dredgers were actually designed and built.
In May of 1845, the Swansea Harbour Master was provided with the sum of £450.00 to purchase a dredger from Totnes in Devon for the deepening of the River Tawe – particularly above the Pottery – although unfortunately there is no record of the type of craft he acquired for this task. In 1875 a new bucket dredger, the Abertawe, was commissioned by the Swansea Harbour Trust, followed by the bucket dredger Number One in 1884.
It is interesting to note that a surviving example of a steam-powered bucket dredger – the SND No. 4 bought by the Sharpness New Docks Company in 1925 – can be seen as a floating exhibit alongside the National Waterways Museum in Gloucester. Also on show at the Canal Museum at Ellesmere Port is the restored steam pontoon grab dredger ‘Perseverance’, which was built in 1934 for work on the Grand Union Canal.
These days, large modern trailing suction hopper dredgers such as the ‘Bluefin’, ‘Marlin’ and ‘Orca’ are used by UK Dredging to maintain the required depths of water at ports like Swansea and Port Talbot although, surprisingly, the history of the trailing suction dredger goes back at least to 1907, when the twin-screw sand pumping hopper-dredger “Lord Desborough” was commissioned by the Thames Conservancy Board. Built by Messrs Ferguson Brothers of Glasgow, it was at the time the largest dredger to be built on the Clyde – her dimensions being 330 ft. by 54 ft. 6 in. by 23 ft. Fitted with double suction pipes arranged to ship inboard, she was capable of raising 4,500 tons of sand per hour from a depth of 70 ft. below water level.