Legs home
Zero from the coast, on purpose: a broke, bare Sloop must always be able to reach port. One from the Reef. Two from the Abyss, and three from the far end of it.
Slipping a gate adds a leg for each one slipped. Smuggler's Charts take one off. The chart's button tells you the number before you press it.
What a leg is
A leg can be quiet, it can turn up a chest about 20% of the time, or it can turn up something with teeth. That last runs from 28% in a Sloop out of the Reef to 45% in a Galleon out of the Abyss, because big ships are easy to find.
A fight on the way home is fought with whatever hull you have left. Win it and the leg is covered. Run from it and you are exactly as far from home as you were, a good deal less seaworthy, and the next leg rolls again.
Why it matters
A career that could reach port in one action could top off hull between every fight and win almost everything. Pricing the way home is what makes every other survival mechanic mean something.