Hydrography at the Port of London Authority
- Talk by John Dillon-Leetch, Port Hydrographer

Report by John Hasselgren


This fascinating and informative talk was given as one of the Small Craft Group’s collaborations with the Royal Thames Yacht Club. 

John started by giving a brief synopsis of his journey from sailing on the West Coast of Ireland, becoming a Yachtmaster, then working in offshore oil and gas before joining the PLA and working up to his present position as Port Hydrographer.

We were then informed a that London was a Trust Port covering 400 square miles, with 95 miles of the river and its estuary and 70 wharves and terminals. By tonnage, 50 million per annum, it is the UK’s largest port. West of London the river is mainly used for recreation, the centre, in London, is mostly used as a road with 90 million passenger journeys, while east of London it is mainly commercial.

The PLA has a Vision Document for the desired future of the Thames, Thames Vision 2050. Here it sets out how it wants the Thames to develop under three main headings:

Trading Thames. Here it looks to be a competitive port, close to the UK’s largest market. Improved connectivity with road and rail infrastructure is its aim, with innovative solutions to expand the use of the river as a means of transporting varied light freight into central London instead of using the roads.

Destination Thames. The river needs to be accessible to all, with visitors drawn to it as the best way to enjoy London with its cultural attractions, and to use its leisure facilities.

Natural Thames. The aim is to have a clean river, free from sewage, waste and pollution supporting greater biodiversity and recreation. It should be valued for its clean air and wildlife as well as being a natural flood defence and carbon sink. More people should be living, working and taking relaxation around the river.

Moving onto the role of Hydrographic Services John described it Statuary Duties. These included the provision of charts for the safety of navigation, data analysis and mapping, provision of river advice and commercial survey work. Who needed these services? Mariners, Harbour Masters, Pilots, terminals and stakeholders. The challenges? Trade growth, available depths, the transition to digital charting, advances in technology and climate change.

Ship owners want their vessels to carry the maximum amount of cargo. This increases draft and minimizes under keel clearance. If insurers agree, this is usually 10% of the ship’s draft. An increase in the accuracy of surveys, leading to perhaps an extra 10cm of water could result in an extra 10,000 containers moving up the river.

Climate change could be a blessing with higher rainfall and rising sea levels leading to a reduced need to dredge. On the other hand it could also lead to extra water running down the river, with overload on the sewer system and increased pollution. Hence the need for the super sewer being built along the Thames beneath the river.

Pilots have their own electronic carry on board system, with the latest PLA charts. The PLA already has 160 pilots and is currently recruiting 16 new pilots a year to allow for natural losses and expected increase in demand. The surveying of the various channels was required to allow pilots to plan safe passage for vessels, making sure there was a safe UKC along the whole of the expected route. This would often require a vessel to reduce speed to allow the tide to rise sufficiently for the draft + 10% rule. To assist this we learnt that the tide heights from tidal gauges were broadcast regularly, together with any deviation from predicted heights. Next year it is expected that dredging will cost up to £200 million. Data recording is important as it allows comparison with earlier surveys indicating which channels are stable and which are likely to require dredging. Bringing a ship up the Thames, perhaps from the Sunk to its berth, is a bit like driving a heavy goods lorry up a motorway where the width of the road halves and bridge heights reduce by 6 metres every six hours.

To assist with the survey work the PLA has three vessels, Maplin, Thames and Galloper. The latter, Galloper, is capable of being loaded onto a trailer meaning that she can be transported to conduct surveys in other waters. Until 1991 all positions were fixed by horizontal sextant angles as GPS was considered too inaccurate for serious survey work. Since then GNSS has been used. In addition to these vessels, new technology is being introduced in the form of remotely controlled or autonomous small vessels, surface or sub-surface, and drones. The side scan sonar equipment can be moved from one to the other. As John Dillon-Leetch explained, the equipment may be fitted into a vessel costing £1.5 million or an AV costing £8 thousand. The AV, he said, needed no crew accommodation, galley nor heads. Also, they are quiet, non-polluting and the data is available in real time.

Responding to a question John explained that the PLA’s jurisdiction extended from Teddington down river and out east to the Gunfleet Sands, south to Margate Sand then west to the Isle of Sheppey.

Moving on to charts, the PLA produces its own portfolios of A2 size charts of the river and estuary which may be purchased. There are also charts at much larger scale for use in work areas or ships’ berths. These may be viewed on the PLA web site, which is well worth checking out. 

As a finale we were shown scans of some of the Estuary’s sunken vessels including the steel barque Dovenby which sank in 1914 with a cargo of guano. Also shown was the SS Richard Montgomery off Sheerness which still contains a cargo of explosives from the 2nd. World War. She is surveyed regularly to check the state of the deck; the masts are currently of concern and there are plans to cut them down before they fall. Just to prove that the PLA do sometimes work on contract to other authorities and businesses we saw a survey of the remains of the power station wall at Bradwell Power Station on the River Blackwater.