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EST. 2013   /   OLD HARWICH, ESSEXTHAMES ESTUARY   ·   SUFFOLK   ·   NORTH NORFOLK
East Coast Tidal
Pilotage AssociationTHE SWATCHWAY ALMANAC

A working almanac for the East Coast

Where the
water makes way.

Practical pilotage notes for the shifting sandbanks, tidal rivers and shoal waters between the Thames Estuary and North Norfolk.

Calculate a crossing window   ↗
51° 56′ N   /   001° 17′ EOLD HARWICH   ·   EST. 2013

A note from the chart table

“On this coast, a little water can open a great many possibilities. Know what lies beneath the keel, and leave yourself room to be wrong.”

Commodore Alistair Finch
RYA YACHTMASTER OCEAN EXAMINER
FIG. 01   /   THE SHAPE OF A SWATCHWAYSCHEMATIC ONLY   ·   NOT TO SCALE
Illustrative cross-section of a tidal sandbank and vesselWATER OVER BANKCHART DATUMTIDE HEIGHT ↑DRYING SAND & MUD

01 / At the chart table

The twelfths calculator

Estimate how much water lies over a bank through a simplified flood and ebb, and find the modelled window for your keel.

Set your passage figures

Use heights referred to the same chart datum. Example figures are illustrative, not a tide prediction.

Positive for drying height; negative for charted depth. E.g. a charted depth of 0.5 m is −0.5.
Under-keel clearance after allowing for draft.
Planning estimate only. This is not a navigational prediction or a guarantee of safe passage. Check current official tide tables, corrections, charts, local notices, actual soundings, weather and an appropriate safety margin. Do not use this calculator alone to make a crossing.

Enable JavaScript to calculate the modelled window.

The model assumes equal six-hour flood and ebb periods around the chosen local HW and the same LW on both sides. It applies 1, 2, 3, 3, 2, 1 twelfths each hour with linear interpolation. Use a corrected local HW and heights; Harwich or Walton reference times need appropriate local corrections. Stream turn is not necessarily HW.

02 / Passage notebook

Read the coast

From the outer estuary to the river mouths: a little preparation goes a long way.

01   /   THAMES ESTUARY

Across the swatchways

Spitway, Whitaker, Ray Sand and the approach to Havengore.

Open pilotage note →

02   /   SUFFOLK RIVERS

Over the river bars

Reading the entrances to the Deben, Ore and Blyth after winter weather.

Open river note →

03   /   ON BOARD

The shoal-draft advantage

Mud berths, kedge warps and the quiet discipline of night pilotage.

Open seamanship note →

03 / Before you cast off

Seasonal
notice board

Shingle, sand and marks do not stand still for an almanac.

SPRINGRecheck buoyage and bar surveys after winter gales. Seasonal marks may be moved, withdrawn or still awaiting attention.
SUMMERDo not assume a track from last season remains clear. Verify current positions and local harbour guidance before departure.
ALL YEARConsult Trinity House Notices to Mariners, local harbour notices and current charts. This board is a reminder, not a live notice service.