by 
The logbook is useful in two ways:;
1) It measures the kilometers already traveled. So you can permanently track how far your ship (with the logbook) has traveled.
2) After a certain amount of kilometers driven, you unlock additional levels. Up to 6 additional levels for your ship are possible.
You can loot the logbook by either capturing ships enters or Buccaneers sunk.
The logbook is then installed in the „middle console“ of your ship. (See the screenshot above. Similar to a module.).
If you want to remove your logbook again, you can do so by right-clicking on it. Depending on the level, this costs a certain amount of Mythos and the experience gained is lost (not the kilometers traveled, but the XP).
Of course, you can take a logbook from ship to ship. However, each upgrade costs Mythos.
Important! The levels you earn with the logbook are only unlocked freely. You still have to earn the XP for that as well. Just as you are used to from your ships. (See: Ship quality)
And what if the ship sinks? Well, then the story of this logbook unfortunately ends. Currently, we don't have the technical ability to save a logbook that sank with its ship. It's simply impossible.
Therefore, what the ancient sailors already knew still applies: if your ship sinks, quickly save the logbook. And the expensive cannons.
English 
German