The problem I ran into: apparently the user.js file is not being read as a JS script. The file-name extension .js is a misnomer, it does not permit all JS syntax.

Look at the contents of this user.js:

user_pref("_user.js.parrot", "Possible error parsing user.js");

user_pref("services.sync.engine.bookmarks", false)
user_pref("services.sync.engine.addons", false)
user_pref("services.sync.engine.history", false)
user_pref("services.sync.engine.prefs", false)
user_pref("services.sync.engine.prefs.modified", false)
user_pref("services.sync.engine.tabs", false)

user_pref("browser.startup.page", 3);

user_pref("_user.js.parrot", "No problems detected");

Observe that some of these lines are missing a semicolon on the end.

If that was considered a syntax error, you'd expect the parsing to never arrive to the last line.

Yet… it does. What's even more strange is that it seems to skip over the lines in between: you'll read "No problems detected" even though the setting "browser.startup.page" does NOT get set to 3.

That's some odd behavior.

Add semicolons, then everything works.

Edit a file: navigationconstants.json.

(Linux path: ~/.config/unity3d/Failbetter Games/Sunless Sea/constants/navigationconstants.json)

You see a bunch of values in this file, such as BaseShipTurningSpeed. Despite what you'd expect, that one only makes a small difference, but let's set it to an extreme value anyway:

"BaseShipTurningSpeed": 99999,

The rest is down to a complex formula that basically means the faster your ship, the slower it gonna turn. There is a trick: accept a very slow base speed, then increase TurboSpeedMultiplier to compensate:

"BaseShipSpeedLimit": 0.000005,
"TurboSpeedMultiplier": 10.00,

Consequences:

1. You'd have to always turbo to get anywhere
2. The Engine Power stat does nothing

With the above, you're so dependent on turbo you may want another hack to "keep it on" with less user involvement. Unfortunately or not, it's also an infinite-fuel cheat:

"FuelUpdatePeriod": 1000,

"DiveTime": 2,