Hollis Tide
  • Stations
  • Pricing
  • The data
  • Notes
See your water
Stations

Know what the water is doing before you need to

Hollis Tide puts a gauge on your wall and a reading on your screen every six minutes. Predictions tell you what the tide should do. A gauge tells you what it is doing, which on a shallow east-coast harbour is a different number often enough to matter.

See your water
One station free for a season, to see whether it tells you anything.
Reading for
Harbour boards  ·  Pilotage services  ·  Sailing clubs  ·  Oyster fisheries  ·  Wildfowling trusts

How a reading reaches you

01

A gauge goes on your wall

Bolted to a quay wall or a pile, below the lowest water you get. One visit, half a day.
02

It reads every six minutes

Observed height, predicted height, and the residual between them, logged at the gauge whether or not anyone is watching.
03

You see it before you need it

On a screen in the harbour office, on a phone, or as a message when the residual passes a figure you set.

Prediction is not observation

Published tide tables are harmonic predictions for a standard port, corrected by a constant. On an afternoon with pressure down and a northerly behind it, the water in your harbour can sit half a metre off the table for six hours. The table is not wrong; it is answering a different question.

The gauge is a pressure sensor and a length of cable

No moving parts, nothing above the waterline to be hit. It reads the head of water above it, temperature-corrects, and sends a figure up the cable. We have gauges in their eleventh season that have had one battery and no other attention.

Six minutes, because an hour is too slow

Six minutes is the standard sampling interval for tidal work, and it exists because surge does not arrive smoothly. An hourly reading can miss the whole of a short surge event, and a short surge event is precisely what puts water over a quay.

The residual is the number worth watching

Subtract the prediction from the observation and what is left is the residual — everything the harmonics do not explain. Flat residual means an ordinary day. A residual climbing steadily for three hours means something is coming, and you have those three hours.

It works when the internet does not

Readings are logged at the gauge whether or not anything is listening. If the connection drops, the record fills itself in when it comes back. A harbour that loses its data during the weather that mattered has bought the wrong instrument.

Your readings are yours

Exportable in full, in formats the tidal community already uses, with no interval beyond which the history is deleted. Long records are how a harbour argues for a scheme, and a long record that lives only inside somebody’s subscription is not a record.

Readings taken each day
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Network uptime, last season
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Gauge to screen
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We had two floods in four years that the tables said were ordinary tides. We can see them coming now, and we can prove afterwards what happened.
Gwen Tasker
Harbour Master, Porthgain

What people ask first

The gauge is bought once; the reading is charged yearly, per station, and not per person looking at it.

Nobody, unless you publish them. Some harbours make theirs open, which we will host for nothing, but it is your decision and reversible.

Yes. There is an ordinary feed in the formats tidal work already uses, and a copy can be pushed to a machine you control.

You are told the same day, from the gap in the record rather than from a visitor mentioning it. Replacement gauges go out by post and fit the same bracket.

What it is for

Most of our stations were installed after an afternoon somebody could not explain. The point of the gauge is that the next one gets explained, and the one after that gets seen coming.