Thames Estuary

The busy channels between the Kent and Essex shores can be treacherous and daunting. But don't be put off ­ Peter Cumberlidge maps out some clear paths.

The busy channels between the Kent and Essex shores can be treacherous and daunting. But don’t be put off ­ Peter Cumberlidge maps out some clear paths

Crossing the Thames Estuary can be intimidating for strangers unfamiliar with shallow swatchways, acres of drying sand and the curious idea that, even out of sight of land, there may be only a few metres of murky water under your keel.

Although the long, fanning banks may look bewildering on the chart, the Thames Estuary is well marked and the legs between buoys and beacons are short. GPS and radar take the worry out of poor visibility and you can have great fun picking your way through the numerous channels between the Kent and Essex shores.

The main shipping route into the Thames, the Princes Channel, can be taken at any tide. However, this deep fairway lies six miles off the Kent coast, and for most boats cruising west towards London it is quicker and more interesting to hug the Margate shore and keep south of Margate Sand via the Gore Channel.

There are various routes through the Thames Estuary. Yachts cruising between the Channel and the Thames turn the corner at North Foreland, usually having just left Ramsgate. With this in mind, I’ll focus on three useful estuary routes: North Foreland across to Harwich; North Foreland across to the Blackwater or the Crouch, and North Foreland up to the Swale or the Medway.

Tidal notes

All things being equal, fast motor boats should cross the Thames Estuary above half-tide, preferably during the last two hours of flood. This gives a margin of error near the edges of banks and over shallow cuts. Towards high water the slackening tide helps iron out any sea. On a crossing towards Harwich, the Medusa Channel is best taken near high water. When crossing towards the Blackwater or the Crouch, a good rise of tide is helpful near the SW Sunk beacon, round the edge of East Barrow sand, over the North Middle bank and, for the Blackwater, through the Swin Spitway. The same applies for the inshore passage through the Gore Channel.

Fast boats should round North Foreland two to three hours before HW Ramsgate, to carry a fair stream through the Gore, and have plenty of rise over the shallow coastal waters off Herne Bay, Whitstable and the approaches to the East Swale, or through the Four Fathom Channel and the approaches to the River Medway.

Tide times

Difference on

HW Dover Difference on

HW Harwich

HW Ramsgate +0030 -0015

HW Harwich +0045

HW Burnham-on-Crouch +0110 +0025

HW West Mersea +0040 -0005

HW Harty Ferry +0125 +0040

HW Sheerness +0135 +0050

Tide heights


Ramsgate 4.9 0.4 3.8 1.2

Harwich 4.0 0.4 3.4 1.1

Burnham-on-Crouch 5.2 0.2 4.2 1.0

West Mersea 5.3 0.5 4.2 1.3

Harty Ferry 5.7 0.6 4.8 1.5

Sheerness 5.7 0.6 4.8 1.5

Conditions to Avoid

A rising tide is usually preferable in the Thames Estuary, and strangers should avoid making passages below half-tide, unless keeping to the main deep-water channels.

It is best not to cross when visibility is very poor, even if you are using GPS, Decca or radar: you run the risk of mistaking buoys or beacons on radar only, and the difference between passing just the right side and the wrong side can be crucial. However, there is no problem with summer haze or patchy mist in quiet weather when navigating on instruments.

Avoid rough weather unless you know the Thames Estuary well. There is danger all around, and the seas can be steep and malevolent over shoals. If you touch bottom, the situation will be serious in a swell but perhaps only inconvenient in calm conditions.

Strong easterlies or north-easterlies bring the nastiest seas into the Thames Estuary. Fresh north-westerlies are unpleasant for a crossing from North Foreland towards the Crouch, the Blackwater or Harwich.


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