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Seamanship on the Thames

Seamanship on the Thames

This article is adapted from information provided by the Port of London Authority, all rights acknowledged.


Navigating the tidal Thames - barrier to estuary

Key rules and regulations

As the tidal Thames is linked to the sea, all vessels need to follow the ‘International Regulations for Preventing Collisions at Sea’ (“Col Regs”). You can read the rules in full here. (There are other local byelaws that relate to rights of way with other vessels, which will be explained further below.)

The main basic rules are: When navigating in the tidal Thames vessels must keep as near to the starboard side of the fairway at all times, as is safe and practicable, or follow the recommended routes shown on the PLA Recreational Users’ Guide. For the avoidance of doubt, this does not mean that you can cross from one bank to another to tack along the river. If you are crossing the river, it is to get to a set location for a particular purpose (i.e. to leave/get to a mooring) and you must not tack, cross or enter the fairway so as to obstruct another vessel proceeding along the fairway.

  • Keep a good look out at all times, behind you as well as in front
  • If you find yourself approaching another vessel head-on, you should sound one short blast and keep to the starboard (right)

When entering the river from a lock, pier or berth do not cross in front of another vessel.

At bridges, use the most starboard arch available to you provided it does not compromise your safety. (See the specific navigation advice for different areas of the river below, for more advice.)

The PLA byelaws contain rules which supersede some of the International Collision Regulations. For example

  • a vessel must not cross or enter a fairway so as to obstruct another vessel proceeding along the fairway.

Thames Barrier


The Thames Barrier has ten spans lettered A to K from south to north:

  • Spans B to G are open to navigation subject to the restrictions described in current General Directions.
  • Spans C, D, E and F are 61m wide with a depth of 5.8m below Chart Datum.
  • Spans B and G are 31.5m wide with a depth of 1.2m below Chart Datum and have depth boards on Piers 3 and 9.
  • Spans A, H, J and K are permanently closed to navigation. Under normal circumstances, and subject to the requirements of partial closures, the northern spans E, F and G are used for inward bound traffic and the southern spans B, C, and D are used for outward-bound traffic.

(The piers of the barrier are numbered 1 to 9, from north to south. There are signs indicating the number of the pier on both east and west sides of the barrier.)

Thames Barrier Control Zone


A permanent Control Zone encompassing the Thames Barrier is established between Margaretness (next to the entrance to Barking Creek) and Blackwall Point (at the O2 Dome).  See our Recreational Users Guide

Usually, traffic is routed through one span in each direction, which will be indicated by green arrows. Spans which are closed to navigation will be indicated by red crosses on the piers of the Barrier.

Do not navigate through a span which is closed to navigation – the gates may be under the water or rotating to a defense position*.

Vessels intending to pass through the Barrier should contact London VTS on VHF Channel 14 at either Margaretness Inward bound or Blackwall Point Outward bound. London VTS will then allocate a span which will be indicated as being available by the green arrows.

Occasionally, all the spans at the Thames Barrier may be closed either for test purposes or because of a predicted tidal surge (the Environment Agency publishes a list of test closures in advance. See either the PLA Notice to Mariners or the EA’s website). When this is the case, you should remain clear and not enter the Thames Barrier Control Zone due to the unpredictable eddies and currents that are produced.

Spans Open to Navigation

Light Signals

Each navigational span of the Barrier has traffic signals on the ends of the adjacent piers to indicate whether the spans are open or closed to navigation. Spans are only ever open to traffic in one direction at a time.

Green Arrows will be shown from the ends of piers either side of a span(s) open to navigation. The arrows point inwards towards the span open to navigation. Red crosses will be shown from the ends of the piers either side of span(s) which are closed to navigation.

Spans Permanently Closed to Navigation

Span A (the southern most span) and spans H, J and K (the northern most spans) are permanently closed to navigation and display closure signs which are also used on closed bridge arched (3 red discs in an inverted triangle)

Overtaking and Manoeuvring Restrictions

Any vessel wishing to overtake another vessel, or any vessel wishing to carry out manoeuvres in the Thames Barrier Control Zone, may only do so with the express permission of the Harbourmaster at London VTS.

Vessels Under Sail

Vessels proceeding under sail between the Woolwich Ferry Terminal and Hookness must keep to the starboard side of the fairway and are not to impede any other vessels. Whenever possible, such vessels should take in their sails and use motor power to navigate through the Thames Barrier.

Small Vessels (under 13.7 metres in length)

All small vessels and craft such as yachts, dinghies, power boats, sculls, rowing boats and canoes not fitted with VHF radio are to navigate inwards through the northern most span and outwards through the southern most span which is open to navigation (indicated by green arrows) and which has sufficient depth of water.

Further detailed information about navigation through the Thames Barrier is included within the General Directions for Navigation in the Port of London.

Navigating in fog or restricted visibility

No attempt should be made to get underway when visibility is less than 200m and should you already be underway during an outing, you should find a safe haven as soon as reasonably practical.

Should the Master of a vessel find themselves navigating in restricted visibility, you must have a comprehensive understanding the International Regulations for Preventing Collisions at Sea, 1972 (COLREGs), in particular Part B (Steering and Sailing Rules) both Section III (Rule 19) – Conduct of vessels in restricted visibility and Section I (Rules 4 to 10 inclusive) – Conduct of vessels in any condition of visibility.

Put simply:

  • A rigorous lookout should be maintained – by sight, sound and any means necessary
  • Navigation Lights are operational
  • Radar, if fitted, is setup appropriately and utilised to assist you in navigating in fog however it should not be solely relied upon but it is an incredibly useful aid to your navigation
  • Navigate at a safe speed to ensure effective action can be taken to avoid a collision.
  • MGN 369 – Navigation In Restricted Visibility contains further guidance.

Small vessels can also vastly improve their detectability by using AIS. An AIS transceiver can also assist small vessel crews in the early detection of ships, as well as showing names, call signs, speeds and headings of vessels in the locality to improve situational awareness.


At times the wash, or waveheight, on the Thames can get heavy. The steep river walls reflect, rather than dissipate, the wash so it can be particularly rough at high water during busy traffic periods. The Thames is classified as ‘Category C’ and ‘D’ with wave heights of up to 1.2m and 1.5m, so vessels should be suitable for the conditions.

PLA Guides

Navigating the Thames in Central London
Navigating the Lower Tidal Thames

Before navigating on the tidal Thames

Ensure you have planned your passage; taken into account the tide times; made bookings with any locks; and checked the weather and ‘Fluvial Flow’ guidance. Check the PLA Notices to Mariners page for anything that may affect your journey, such as river closures and bridge maintenance.

Everyone on board a recreational craft navigating on the tidal Thames should wear a life jacket. The river is cold and fast flowing and can be harsh and unforgiving.

Please also see the PLA Thames recreational users guide for the upper Thames and the lower Thames - Broadness to Medway

Pre-passage checklist for cruisers

  • check your engine is running satisfactorily
  • check your bilge pumps operate correctly
  • check the stern gland greaser is topped up and operates correctly
  • check the horn is working correctly
  • check the steering is working correctly
  • check your anchor is correctly attached and ready to deploy (See Equipment section below)

Rowing and paddling

The PLA has produced an excellent guide that should be read by any GYC member taking a canoe or rowing boat on the river.

Entering the tidal River Thames

Contact “London VTS” with:

  • Name of your boat
  • where you are entering the tidal Thames and your destination
  • The time you expect to be on your way
  • how many people are on board
  • VTS can pass any pertinent navigational information to you too, such as river closures or bridge arch closures.

Always be aware of traffic moving up and down the river and enter the tidal Thames only when safe to do so.

Marine VHF radio

GYC requires that all cruisers to carry VHF. GYC Sailing Dinghies do not need to carry VHF, but they must be accompanied by a safety boat that does carry a VHF.

You should monitor VHF Channel 14 between Teddington and Dagenham (Crayfordness). Below Crayfordness, monitor Channel 68 until Southend Pier where Channel 69 then takes over.

If there is no VHF radio on board (or is broken), the person in charge of navigation of the vessel should report to the London Vessel Traffic Service (VTS) by telephone (0208 855 0315 west of Dagenham, 01474 562215 east of here) prior to entering the tidal Thames.

It is recommended that fixed VHF radios in Cruisers support DSC. The club group MMSI is: XXXXXXXXXX

An RYA ‘Short Range Certificate’ (SRC) is the minimum requirement to use a VHF or VHF DSC radio (unless It is an emergency situation when anyone may use the radio to call for help) as well as appropriate licenses from OfCom. This training is provided at GYC.


An AIS transponder (Automatic Identification System) is of a great benefit. An AIS transceiver can assist small vessel crews in the early detection of ships, as well as showing names, call signs, speeds and headings of vessels in the locality to improve situational awareness.

Combined with a DSC equipped VHF radio, the AIS makes it easy to place a VHF call to a specific vessel rather than on the 'hailing' channel. This can greatly improve safety. For example, a ship is about to manouver and can see a sailboat approaching; Using AIS to find the vessels MMSI number, they can call the actual yacht to confirm intentions, rather than a very general and confusing call to the 'yacht approaching Erith'.

Vessel construction and equipment

The tidal Thames is categorised by the MCA (Maritime Coastguard Agency) as a ‘Category C’ waterway down as far as Gravesend. This means that you can expect wave heights of 1.2m, so it is important to ensure your vessel and the equipment it carries is up to the task. (This increases to ‘Category D’ downriver of Gravesend.)

We recommend the following equipment when navigating on the tidal Thames:

  • Life jackets: approved by MCA or under the Marine Equipment Directive (MED), or should comply with BS EN 396: Life jackets and personal buoyancy aid of 150N, or BS/EN 399: Life jackets and personal buoyancy aids of 275N
  • a VHF set (mandatory for some vessels)
  • mobile phone (in a waterproof pouch)
  • water resistant torch
  • suitable boat hook
  • appropriate first aid kit
  • navigation lights if navigating during darkness or reduced visibility
  • ropes for mooring the vessel and for towing
  • minimum of one 12kg anchor, attached to a designated strongpoint by 5 metres of 6mm short link chain and 25m of 12mm rope.

Additional information from the RYA:

Licensing and certification

Although there is not a legal requirement for the person in charge of a recreational craft or ‘pleasure vessel’ to have a formal qualification, the tidal Thames is not for novice or inexperienced people. A good degree of boating knowledge and experience is needed before venturing on to this complex and challenging river.


  • vessels that are hired or chartered are not considered to be pleasure vessels.
  • a vessel carrying more than 12 passengers is not classed as a pleasure vessel, but would come under the definition of a ‘passenger vessel’. The vessel and the skipper would then require appropriate licences from the Maritime Coastguard Agency (MCA). Contact your local MCA office for further details.