A French chart is not really a foreign object. That is the first thing to understand, and it is reassuring. The symbols on a SHOM chart and the symbols on a British Admiralty chart come from the same international rulebook, so most of what you already know carries straight across. The differences are in the labels, a handful of conventions, and the language of the few words that are spelled out in full.
I learned French charts the hard way, by squinting at a paper sheet off the Glenan in failing light and realising I did not know whether a particular abbreviation meant sand or shingle. So here is the visitor's version, the things that actually matter when you are reading a SHOM chart under pressure.
The good news: it is all INT 1
Chart symbology is standardised worldwide under a system the hydrographic offices call INT 1. SHOM, the French hydrographic and oceanographic service, aligns its charts to that standard, exactly as the UK Hydrographic Office does. A wreck symbol is a wreck symbol. A lateral mark is drawn the same way. An isobath, the line joining points of equal depth, looks identical. The colour logic is the same too: deep water is white or pale blue, and the shallows step through blue, green and the drying tints.
So you are not learning a new visual language. You are learning a new set of captions for a language you already read.
The reference you actually want
The single most useful thing you can buy is the SHOM publication known as Book 1D, the French equivalent of the UK Chart 5011. It is a reference of chart symbols, abbreviations and terms, runs to around 122 pages, and crucially it lists every term in both French and English side by side. That bilingual layout means you can sit with a SHOM chart and decode anything you do not recognise without a dictionary. For the price of a few marina nights it removes nearly all the friction. I keep a copy at the chart table and reach for it more than I expected.
If you carry SHOM charts to satisfy the French carriage rules, and you should read up on charts for French waters to understand why, then Book 1D is the natural companion that makes those charts legible at speed.
Depths and heights: read the small print
Soundings are printed as numbers across the chart, the depth in metres at the lowest astronomical tide. A tilted or sloping figure is the convention for a depth, and SHOM uses metres, so a 9 means nine metres at the lowest the tide is predicted to fall. Drying heights, the patches that uncover, are printed underlined, giving the height the patch dries above datum.
The thing to internalise is the datum. SHOM references soundings to the lowest astronomical tide, the same datum the French tide tables use. That means the printed depth and the tidal height from the almanac add cleanly, which is the entire reason the system works. To turn a charted depth into the water you will actually float in, you add the height of tide, and the height of tide on this coast is governed by the coefficient. If that link is hazy, the French tidal coefficient is the piece that ties the chart number to the real depth under your keel.
Seabed abbreviations: the ones to memorise
The nature of the seabed is printed in small abbreviations, and these are French rather than English, so they are worth learning before you anchor anywhere serious. The common ones:
- S for sable, sand.
- V for vase, mud.
- G for gravier, gravel.
- R for roche, rock.
- Co for corail or coquilles depending on context, coral or shell.
- A for argile, clay.
So a chart marked S.V tells you sand over mud, which is good holding. An R warns you that your anchor may not bite and your chain may chafe. On the Mediterranean side you also need to watch for the protected seagrass, which is a separate concern entirely; the posidonia anchoring ban in France explains why a green meadow on the seabed is now a legal as well as a holding issue.
Lights, marks and the buoyage convention
Light characteristics are written in the international shorthand and read the same as at home: the abbreviation for the rhythm, the colour, the period in seconds, the elevation, and the range in nautical miles. A light shown as Fl(2)WR.10s is a group-flashing white and red light, two flashes, ten-second period. SHOM uses the identical notation, so nothing new to learn here.
Buoyage is where a visitor must keep their wits. France uses IALA Region A, the lateral system where, entering harbour, red marks are kept to port and green to starboard. That is the same as the rest of Europe and the opposite of the Americas. The chart draws the marks to the Region A convention, so if you have crossed from the US side, fix the IALA Region A buoyage in France in your head before you read a French chart, because the colours are doing the opposite of what they would back home.
A few words spelled out
Some things on a French chart are not symbols but words, and a small vocabulary saves confusion:
- Roche, rock; rochers, rocks.
- Epave, wreck.
- Balise, beacon; bouee, buoy.
- Phare, lighthouse; feu, light.
- Mouillage, anchorage; interdit, prohibited.
- Zone reglementee, regulated zone.
Seeing mouillage interdit on a chart means anchoring is forbidden there, which on parts of the Riviera now applies to the seagrass beds. None of this is hard, but reading interdit and understanding it is a forbidden zone, rather than guessing, is the difference between a relaxed afternoon and a fine.
A few conventions that catch British eyes
Beyond the captions there are small habits worth flagging. Magnetic variation on a SHOM chart is given in the compass rose exactly as on an Admiralty chart, with the annual change noted, so update it for the year you are sailing. Scale is shown as a ratio, and SHOM produces a sensible spread of harbour-scale plans inside the coastal charts, so do not assume the small-scale passage chart carries enough detail for a tight entrance; reach for the larger-scale plan. Heights of lights and of bridges are given in metres above the high-water reference, not above the sounding datum, which is the same split you are used to but worth remembering when you compute clearance for a mast under a bridge.
Tidal information is sometimes printed on the chart itself, as a small box of tidal stream data keyed to a reference port, with rates for springs and neaps. On the Brittany charts this is genuinely useful, because it gives you the stream where you are without opening a separate atlas. It scales with the coefficient just as the almanac tables do.
Reading the chart and the tide together
The last skill is not really about symbols at all. It is reading the chart and the tide as one picture. A SHOM chart of North Brittany is a maze of drying rocks and isobaths, and it only makes sense when you overlay the height of tide and the direction of the streams. The same drying rock that is a clear hazard at low water springs is six metres under your keel at high water, and the channel between two ledges only carries a fair stream for part of the cycle. That is why experienced cruisers read the chart with the almanac open beside it, and why the symbols, once you know them, are the start of pilotage rather than the end of it.
Get Book 1D, learn the seabed letters, keep the buoyage convention straight, and a SHOM chart stops being foreign within a day. The detail on it is excellent, the survey behind it is meticulous, and once the captions make sense it is one of the most trustworthy chart products you can carry on this coast.
