Fathom

01 Gazetteer

01 How to play

Every day there is one island hidden in a square of fog, the same island for everyone. Tap or click anywhere on the sea and the ship sails there and drops the lead. The number written where it lands is the depth in fathoms (a fathom is six feet, about the span of a sailor’s arms). The closer you are to land, the shallower the water.

Far out, the line runs out before the lead touches bottom: that’s no bottom at forty, and it means the island is a long way off. Once you find bottom, follow the water as it shoals. Cast on the island itself to make landfall. You have ten casts before the fog closes in for the day. If three casts in a row find no bottom, keep an eye out for birds.

When you find it, the fog lifts and the island is charted, with a name and a line of history for every place on it. Share your casts if you like: the squares go from black (no bottom) through blue and green to yellow (shallows), and end on the island. A new island surfaces at midnight, your time.

02 The lead line

Before sonar, depth was found by hand. A leadsman stood in the bows and swung a lead weight on a long line, let it sink, and read off the depth when it hit bottom. The hand line was marked with scraps of leather, calico, bunting and serge at 2, 3, 5, 7, 10, 13, 15, 17 and 20 fathoms, different to the touch so they could be read in the dark. At a mark he called “by the mark seven”; between marks, “by the deep six.” On the Mississippi, two fathoms was “by the mark twain,” which is probably where Samuel Clemens, a river pilot before he was a writer, found his pen name.

The bottom of the lead was hollowed out and filled with tallow, which brought up a sample of the seabed. On old charts you see it written beside the soundings in abbreviations: s for sand, sh shells, g gravel, m mud, oz ooze. A good navigator in fog could find their way by depth and bottom alone. Here the bottom is mostly for flavour, though sand and shells do tend to lie nearer the shore.

03 How it’s made

Each day’s island is a coast from Landfall, the chart-drawing toy on this site, chosen by a random number that comes from the date, so everyone gets the same island without anything being sent anywhere. The depth at any point is its distance from the coast, about one fathom for every eleven units of sea, with a little noise so the seabed has banks and hollows. Beyond forty fathoms there’s no bottom.

When you find the island, the same code that draws Landfall’s charts draws this one. You can open it there, keep it, rename its places, or send it to the atlas.

Your casts and results are kept in this browser only, so you can come back to today’s game and keep a streak. Nothing is sent to me or anyone else. There are no accounts, cookies or trackers.