Portolan

Your chart begins as an empty sheet of paper.
Not fogged. Not greyed out. Empty. There is no wind arrow on it, no current, no
coastline, no sounding — because nobody has been there and written one down. Everything
that ever appears on that chart, you put there yourself, one measurement at a time.

Four instruments and a great deal of patience
You have what a ship in 1821 actually carried, and nothing else.
Compass and log — a course and a speed, hour after hour, which is a position

only for as long as the sea agrees with you.

Sextant — the sun at its highest gives you a latitude. It gives you nothing at

all about your longitude, and it gives you nothing on a cloudy day.

Thermometer — sea temperature, hourly. It is how you find the edge of a current

before you can see it.

Lead line — the bottom, if the bottom is within 150 metres. Where it answers,

You are closer to land than you thought.

Your mistakes are the data
This is the mechanic the whole game is built from. You reckon your position from course
and speed. Then you take a sight, and the sight disagrees with your reckoning. That
disagreement is not a failure state — it is the current, measured. The difference between
where you thought you were and where you are gets written back along the track you
sailed, cell by cell, and becomes an arrow on your chart.
Navigate carelessly and the arrows land in the wrong squares. The chart will go on lying
to you about that stretch of ocean for as long as you let it.
A plan is worth exactly what your chart is worth
Lay marks across the water and the game tells you the date you reach each one, the days
of water you will have left when you get there, and — in plain numbers — how much of that
forecast rests on cells you have actually measured. On a blank sheet the certainty reads
[b]0%[/b], and the panel says so outright: the rest is extrapolation, not prediction.
That number is the reason to survey. Not points. Not currency. The planner simply stops
lying to you.
Water is the second deadline
Twenty-four sailors, a hundred days of provisions, fifty days of water. Water runs out
first, and it is bought with time alone — days idle in harbour, or hours spent putting a
boat ashore in a bay that may or may not have a stream in it. Whether a stretch of coast
gives water is a fact about that coast, fixed from the moment the world was made, and
finding it out is the same loop as finding a wind: go, look, write it down.
Ice closes the north in its season. Cyclones close the south in theirs. You do not learn
this from a tooltip. You learn it by arriving.
The ship is expendable. The chart is not.
Run out of water at sea and the ship is lost. You may take a new one out of your home
port with [b]the same chart[/b] — every rose, every sounding, every watering place you
ever wrote down. That is the whole proposition of the game in one line: the voyage ends,
the knowledge stays.
What this is not
No combat. Nothing shoots at you.

No economy. No gold, no cargo prices, no shops, no upgrade tree. Provisions are

Counted in days, not coins, and buy nothing but time.

No quest log. Nobody hands you a checklist. Where you sail is your own idea.

No sail trim. You set a heading and stand the watch. The interesting decision

is where, not how tight the sheets are.

The world
The Atlantic as it is — real coastline, sixteen real harbours from Falmouth to Cape Town,
real wind belts, real calm latitudes — and a generated ocean that plays by the same rules
when you want water nobody has ever charted. Every world is a seed: the same seed gives
the same ocean, so a passage that beat you can be sailed again.