The tide decides when you leave

A short table of times and heights on the left. On the right, a chart extract: soundings scattered across it, a buoy, a lighthouse with its character beside it, a compass rose.

Between them they answer the only two questions that matter before a passage. Where is it shallow, and when can I go.

Why a chart rather than a yacht at sunset?

Because the chart is what sailing is made of and the sunset is what it's photographed as.

Sailing merchandise is silhouettes on orange water, rope knots and anchors. None of that is consulted by anyone. A chart is consulted before every single trip, and reading one is the actual skill — depths, hazards, the mark you have to leave to starboard.

It also happens to be one of the most beautiful technical drawings anybody makes.

What does the tide table add?

Time, which is the constraint the whole sport runs on.

Nobody who sails chooses their departure. The tide does — a drying harbour, a gate over a sill, a stream that runs four knots the wrong way for six hours. Four rows of times and heights is a picture of a life organised around water.

Two documents side by side also gives the design its structure: a dense table against an open drawing, which is the same contrast a data print needs to avoid reading as a spreadsheet.

Can it reproduce a real chart?

The seabed is a fact. The published chart is a hydrographic office's work.

National hydrographic offices produce and license charts, and they hold rights in that cartography — the styling, the symbol set, the typography and the sheet as a whole. Some are firm about it. Depths and coastlines are facts about the world; the drawn sheet is a document.

Which is exactly where a land map sits too: draw the soundings, invent the styling, and keep the sheet numbers generic. The symbol conventions themselves are international standards rather than anybody's artwork.

What makes it personal?

A specific stretch of water and a specific tide.

The entrance somebody has come into in the dark forty times. The passage they've been meaning to do for five years. The tide table for the morning a boat was launched, or the day of a crossing.

A light's character — the pattern of flashes written beside a lighthouse symbol — is one of the best small details available. It's a real code, it means something exact, and it's utterly opaque to anyone who hasn't learned it.

Does it work for a boat or a club?

Both, and for a boat it's a proper record.

A yacht's name, her draught and her sail number set as a title block turns the design into her paperwork. For a crew who did a passage together, the chart of that passage with a date is the equivalent of a crew list — the boat is the unit here too.

Club burgees, class insignia and regatta marks belong to those organisations, so a club's own comes with the club's agreement.

Does it suit other water?

Any water with a chart or a table.

Sea kayaking has tidal streams and overfalls. Inland waterways have lock and mileage charts, which are a wonderful vertical format. Diving has site plans with depths and slack water times. Rowing on tidal rivers has both.

The lock chart is the underused one — a strip of numbers descending down the chest, which is an unusual and very readable shape.

Does it print well?

Yes, with the soundings edited down hard.

A real chart's depth figures are tiny and numerous, and reproduced faithfully they become speckle. The printed version wants perhaps a fifth of them, set much larger — enough to read as soundings without pretending to be navigable. The symbols, rose and coastline are all clean line work.

Navy is the obvious ground and it earns it. Two inks — cream for the chart, with a warm accent on the buoy or the light — keeps the whole thing calm.

How do I get one made?

Describe the water at JustOG — which entrance, which tide, and what the light's character is. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.

Designs other people have published are in the shop.

You don't get to pick the hour. That's the appeal.