High and low water anywhere in the world, real water depths near a reference port — and the rule that tells you when you may add it to a charted sounding.
Published 27 September 2026 · 8 min read
Contents
Where to find the tide in Solano
Two sources, two titles: "Tide" or "Water depth"
What you may add to a sounding — and what you may not
Reading the chart: the two curves and the surge
Tides at anchor: how much chain
The warnings, and why they are there
What Solano's tide does not do
1. Where to find the tide
Drop a point at sea and run the Quick forecast (☀️). In the button row of the results panel, a 🌙 Tide button appears: it unfolds the curve below the Marine section.
Why isn't it on by default? Each display costs one request to the data provider. Tides matter in some situations, not all — so not everyone pays for them. On a land point the button does not appear at all.
The tide also shows up on its own inside the anchorage analysis, over the three days analysed, right above the sounding and the seabed type — that is where it is most useful (see §5).
2. Two sources, two titles
Look at the block's title first. It is not decoration: it states where the figures come from, and therefore what you are allowed to do with them.
🌊
"Tide" — model source. A global ocean model (~8 km grid) that works everywhere: offshore, on an island with no tide table, in a Greek anchorage at the head of a bay. It gives high and low water times and a tidal range.
⚓
"Water depth" — tide-table source. When a reference port can be attached to your point, Solano switches to its official tide table: times and heights are the hydrographic service's own, referred to chart datum. The banner names the station and its distance; in France the coefficient appears next to each tide.
Attachment is not merely a matter of distance. The station must be within 20 km and the point's tidal regime must resemble the station's (ranges within 15 % of each other over two weeks). A station 3 km away but on the far side of a sill, with half the range, is rejected — and rightly so: its times would be of no use to you.
The first visit often gives the model, the next one the tide table. The regime comparison runs in the background and is then remembered for months. If you see "Tide" on a point where you expected a port, reopen it a little later.
3. Adding it to a sounding: yes, no
This is the most important point on this page, and the reason the two titles differ.
Tide-table source ("Water depth"): yes. It is a real height of water above chart datum — the same datum as the soundings on your chart. Sounding + height of water = depth under the keel at that moment. That is the calculation every sailor makes.
Model source ("Tide"): no. That model is referenced to global mean sea level, not to your chart's datum. The value shown is a departure from a reference, written with an explicit sign (+1.20 m) precisely so it cannot be reread as a height. Adding it to a sounding would give a meaningless number — and the error would tend to announce too much water.
What stays correct on the model path are the differences: between two instants on the same curve, the unknown datum cancels out. Hence the only two things we display: the times of the stands (within about ten minutes on an open coast) and the range (within a few per cent).
This was not free to establish: estimating chart datum from the model's own archive was tried, then dropped after comparison with the Canadian tide tables — the estimate moved away from the true datum instead of towards it, while announcing too much water. The measurements are detailed in The Solano method.
4. Reading the chart
Two curves are superimposed. The solid line is what you will get: the tide plus the weather's effect. The dotted line is the tide alone — astronomical, the Moon and the Sun. The coloured band between them is the difference.
That difference is the surge (a negative surge when it goes the other way): weather moves water. A depression sucks the level up, a high crushes it down, and wind blowing onshore piles water up ahead of it.
A tide table contains no surge at all. It knows only astronomy. The correction Solano adds comes from a dedicated surge model (Météo-France HYCOM2D, ~4 km grid) that accounts for the wind as well as the pressure — and that changes the figures: on 21 September 2026 in the western Mediterranean, pressure alone gave −6 cm where the full model gave −14 cm.
Hovering the curve, the tooltip names the correction applied at that hour: surge where the dedicated model covers the lead time, barometric effect beyond its horizon (about four days). That is deliberate: a continuous ten-day curve that states plainly, hour by hour, what it contains is better than a step in the middle.
The band is not a detail everywhere. The gap between the two curves is around 2 % of the range in the English Channel, but up to 20 % off Newfoundland. Where the range is small and the weather lively, it is the weather that decides the water depth, not the Moon.
5. Tides at anchor: how much chain
In the anchorage analysis, the tide sits right beside the sounding and the seabed type, because those are read together when deciding on a length of chain.
Two figures appear. The next tide, large — the range to come. And, only if the spread justifies it, a second line: "up to X m within 3 days".
Why that second figure? In the Brest roads, over a three-day window, the range goes from 1.70 m to 4.28 m: neaps turning into springs. A single figure would have you undersize the chain for the night after next. In the Mediterranean the same spread is 9 cm — the line disappears, since it would teach you nothing.
Below one metre, the range is written with two decimals: "0.0 m" would read as missing data, when it is in fact an answer — in the Mediterranean the range is a few centimetres.
And here too, the note under the sounding switches with the source: with a tide table it invites you to add them, with the model it says plainly that the value does not add to the sounding. Two figures side by side on screen are not necessarily two figures to add.
6. The warnings
Four messages may appear below the curve. None of them is a bug: each states a known limit instead of hiding it.
⚠
"Range probably underestimated." On the model path, always. An 8 km grid cell does not make a funnel resonate: −6 % measured at Halifax, −9 % at Saint John, −20 % at the head of the Bay of Fundy. The more enclosed the site — bay, estuary, head of a ria — the more the true range exceeds the one shown. Solano flags it rather than quietly correcting with an invented factor.
📍
"Figures from the X tide table, N km away." The times and heights are exact for the station named. Behind a sill or at the head of an estuary, your regime may differ from its own.
🗺
"Tidal regimes not compared here." At the head of a bay the model is sometimes blind: a drying area falls on a land cell, so there is nothing to compare. Attachment then rests on proximity alone (under 8 km) — which is useful, and is stated.
ⓘ
"Predictions for this station are modelled". Alongside their instrumented ports, some tide-table services publish stations whose predictions are computed rather than adjusted against a local tide gauge — twelve of the thirty-eight Irish stations, for instance. The heights are still on chart datum, so they can be added to a charted sounding; what is at stake is their accuracy, to within a few centimetres. They are sometimes the only station on a whole stretch of coast: Solano keeps them and says so, rather than leaving a gap.
Finally, a reference level still being built is announced as provisional: on the first visit to an area, Solano does not yet have the year of archive that anchors the axis. Come back a little later and the note is gone.
7. What Solano's tide does not do
📕
It does not replace an official tide table. Where Solano attaches a port, the figures are the hydrographic service's — but the app is not an approved service, and elsewhere they come from a model.
🌀
It does not give tidal streams. Currents come from a separate model, shown as a map layer. Slack water for the stream does not coincide with the stand of the tide — do not infer one from the other.
🏞
It resolves nothing in a river. Tidal bores, tidal barrages, narrow estuaries: neither the model nor the interpolation of a harbour curve means anything there. Stations of that kind are in fact discarded when their service publishes no curve, for exactly that reason.
ⓘ
"Curve reconstructed between the stands". In the United Kingdom the official tide tables give the times and heights of high and low water for free, but not the line in between. Solano computes it the way a sailor would by hand, with the rule of twelfths. The figures that matter for a sounding — the time of low water and its height — are still the tide table's own, and exact; it is the slope between two stands that is approximated, to within a tenth of the range (measured: 3 to 16 cm RMS). Another consequence of the same subscription: British tides stop at six days, where the model gives ten.
🌍
Tide-table coverage is not worldwide. Canada, France, Ireland and the United Kingdom so far, with more countries as their services publish a usable interface. Everywhere else it is the model — so times and range, not water depth.
Going further
The detail of the computation — refining the stands, the conditions for attaching a port, where the surge is added and where that is forbidden — is in The Solano method. For chain length and shelter protection, see Analysing an anchorage, and for wind sea and swell, Reading the weather on the map.
Disclaimer: Solano is not an approved hydrographic service. The times and heights shown are indicative and do not replace official publications (SHOM, national hydrographic services). The decision remains the skipper's responsibility.