builder's blueprint book, how to use them ?

[Roumata]

although i have discover all the map of Belerion DLC and i'm advanced in quests, i have three books on my inventory "builder's bluprint book" and i don't understand how to use them. At dock, and shipyard i have no option to use them, i can't use them on ship customization screen etc....anyone can give me some advices, i should have missed something
:) thanks

[Spawnling]

They are required to learn upgrades for your ship in the knowledge tab.

e.g. Once you'be built a new Sail at a dock, you'll have the option to learn an upgraded version of that sail for a builder's blueprint. Then you can upgrade the Sail at a dock.