The waters
Coastal Waters, steps 1 to 3. Shallow and safe-ish. Small teeth, small coin. A chest here holds 12-28◆ and better further in. Roaming it: Reef Shark, Young Serpent.
The Broken Reef, steps 4 to 6. Wrecks and shoals. Things with tricks live here. A chest here holds 45-85◆ and better further in. Roaming it: Diving Serpent, Shellback, Siren Spitter.
The Abyss, steps 7 to 10. Black water. Great treasure. Greater appetites. A chest here holds 130-250◆ and better further in. Roaming it: Kraken, Leviathan.
Reading it
⚔ is something with teeth. ✦ is a chest. ≈ is calm water. ❖ is something that wants a decision from you. ⚖ is a merchant. ✝ is a wreck. ? is fog, and fog can be a monster, a chest or a decision, and you will find out by sailing into it.
From where you are, you can sail to the nearest waters in the next row, and the ones you can reach pulse. You see the row you are on, the water straight ahead of you, and the things that sit across the chart from port: the gates, the still water and the Maw. The waters either side of straight ahead are out of sight until you are level with them, so choosing your way is the first decision of every step. A Sloop sees the next row in full and the water straight ahead beyond it, a fog bank or a man with a chart shows you more, and a Sounding Lead shows you what is behind every ? in sight.
Water you run from
Running is not a way forward. Flee a fight on the chart and you lose the step, and that patch of sea stays shut for the voyage: it holds it now, and it is marked ✕. A Sloop's clean break is the exception, and that is most of what a Sloop is.
What else is out there
A ❖ is a bell under the water, a man on a raft, a hatch nailed shut from the inside. Each gives you a choice, each choice gives you a hint, and the hint is not the whole of it.
A merchant sells at sea what Saltmouth sells cheaper, paid out of the hold: a patch kit for 45◆, 20 hull for 40◆, a fitting for 220◆.
The bottom
Rows 4 and 7 are held by the gates. The last water before the end is flat calm and mends 60% of your hull. It wants you whole. Row 11 is the Maw. It has no gate behind it, because there is nothing behind it.