accessing Greater London, main deep-water routes were the Princes-Queens Channel and the South Channel to the south, to a lesser extent the Kings Channel and the Swin to the north. The Swin was used by barges and leisure craft from the Essex rivers, and coasters and colliers from the north east. These channels were made up of natural troughs; Yantlet Channel (Sea Reach), Oaze Deep, Knock John Channel, Black Deep/Black Deep Channel which have been much-marked. These are separated by slow-moving sandbanks with names such as the East and West Barrows, the Nob, the Knock, Kentish Knock, the John, the Sunk, the Girdler, and Long Sand/the Long Sands. Shallow-bottomed barges and coasters would navigate the swatchways at flood tide, and would cross the sand banks at spitways, points where the water was least shallow, and just deep enough at that point of the tide. If they missed the moment they would heave to (lay anchor) and wait for the next tide. Recreational craft are expected use channels most suited to the size of their vessel. Their main guide says to use when navigating to or from: the north: the Middle Deep, Swin, Warp and Barrow Deep. the south/due east: the Horse and Gore and Four Fathom Channels. To cross the south-east quarter of the estuary large vessels use Fisherman's Gat, and small vessels to were expected to use Foulger's Gat. Navigational marks History Provision of buoys and beacons for the purpose of navigation came relatively late to England (compared to the Netherlands, for example). Instead, coastal navigators and pilots relied on the use of transits (the alignment of prominent structures or natural features on land) for guidance. In 1566 Trinity House of Deptford (which oversaw pilotage on the Thames) was empowered to 'make, erect and set up [...] beacons, marks and signs for the sea' (albeit at its own expense). Not long afterwards, the decay of the steeple of Margate Church (an important landmark for negotiating 'the Narrows', a complex route between sandbanks used by vessels sailing to or from London along the North Kent coast) led to Trinity House marking the Narrows with buoys in the late 16th century. In his coastal survey of 1682-93, Greenvile Collins records five buoys around the Narrows, just north of Reculver, on the southern approach to the Thames. The Swin (the northern approach) was marked with buoys at the easternmost points of the