Frequently asked questions

A tide clock with a hand, like the ones found in seaside homes, except that the hand is driven by a computation rather than by a mechanism running at a fixed rate. It shows, at all times, where the tide stands at your port: high water, low water, rising, falling, and how long until the next turn.

HMC (for Horloge des Marées Connectée) is the name of the instrument and of the clock module that drives it.

A traditional tide clock runs at a fixed rate, on an average lunar period of 12 h 25 min. The real tide does not keep that rhythm: it runs early or late every day under the pull of the Moon, the Sun and the shape of the coast. An unconnected tide clock can drift by more than an hour a month.

The HMC computes the real tide of your port with the CNES mathematical models and positions the hand accordingly. It does not drift and never needs resetting. Details on the Accuracy page.

No, and the difference matters. A tide gauge is a sensor: it measures the water level of the moment, where it is installed. It tells you what the sea is doing, not what it will do. A tide clock answers the other question, the one people ask on the coast: what time is the next tide, and where are we now.

The HMC predicts; it does not measure. We do, however, check our predictions against the reference tide gauges, port by port: on the Tide times page, a blue pin marks the ports where that check exists.

No. It is a dial and a hand, nothing else. You read it at a glance, like a wall clock, without switching anything on. The app is only used for setting it up and choosing the port.

Not on the dial, and that is deliberate. The HMC is a clockmaker’s instrument: a hand on a dial, nothing else. A digital readout or indicator lights sit badly on such a dial and spoil what makes it worth having. We are studying a solution for future versions, one that will give up nothing of the instrument’s look.

The HMC does know the coefficient and the water heights, though: it computes them for your port along with the high and low water times, and keeps them available in its settings interface. Above all, it can warn you: as a spring tide approaches, the clock emails its owner as soon as the coefficient exceeds a threshold you set yourself. You choose the threshold; it writes to you.

For French ports, from the mathematical models of CNES, the French national space agency and the reference in coastal oceanography: the so-called “harmonic” computation, explained in the next question. For ports abroad, from the relevant national hydrographic services. The source is named under each table on the Tide times page.

The tide is the sum of several regular motions: the pull of the Moon, the pull of the Sun, the effect of their changing distance, the shape of the coast that amplifies or delays the wave. Each motion has its own rhythm, known exactly, like a musical note that always comes back at the same interval. They are called harmonics, by analogy with sound.

The harmonic computation measures, once and for all, the weight of each “note” in a given port, then adds them up for any moment in the future. That is how hydrographic services the world over produce their tide tables, and that is what the HMC does for your port, continuously.

As accurate as the official hydrographic models: predictions within a few minutes for the times of high and low water, over horizons of several years. We check them continuously against the water level actually measured in ports fitted with a tide gauge. The method and its limits are set out on the Accuracy page.

Today, 1,031 ports across 7 countries (France 182 · Spain 36 · Portugal 25 · United Kingdom 56 · Ireland 37 · Canada 106 · United States 589). The full list, with the map, is on the Tide times page: pick the country, the region, then the port. Your port is missing? Tell us: coverage grows with requests.

No. The HMC is an instrument for the home and for planning, not a nautical document. For navigation and safety, only the official tide tables and notices of your national hydrographic service apply.

Not permanently. The instrument runs on a rechargeable battery designed to last several months depending on use, and recharges over USB. So it goes where you want it: a wall, a shelf, a boat.

Yes, through your home Wi-Fi (2.4 GHz), but not continuously: it connects briefly to synchronise and receive its updates, then the hand moves on its own. A network outage of several days does not disturb it.

Two ways, your choice. With the HMC Pilote app on an Android phone, over Bluetooth: the app finds the instrument, you give it your Wi-Fi network and your port, and that is it (the iPhone version is in development). Or from the browser of your phone or computer, Windows or Mac: the instrument opens its own Wi-Fi network for the duration of the set-up, and a page walks you through it, nothing to install.

At first start-up the hand makes a full turn to find its reference mark, then moves to the tide position.

From the app, in a few seconds, without restarting or resetting the instrument. The hand repositions itself on the tide of the new port.

On their own, over Wi-Fi. Every update is signed and verified by the instrument before it is installed: an update that does not come from us is refused.

For the service that keeps the instrument alive: computing the tide of your port, updating it as hydrographic campaigns are published, adding new ports, and updating the instrument itself. Terms will be announced at launch; write to us to be kept informed.

The HMC is designed and developed in France. For its launch it is fitted into the dials of Maison NAUDET, a French maker of measuring instruments since 1860. The computation service is hosted in France.

Distribution at launch is handled by Maison NAUDET, the project’s industrial partner. To be told when it is available, leave us your details. Project news is on the News page.

Yes, that is what it was designed for. The HMC clock module fits inside your case and under your brand: a module, a dial, a hand, and the computation service behind them. Everything is on the OEM page.