You are a craftsman who has been working with ships long enough to be considered an expert. What drove you to start working on waterborne vessels? Were you born in to the trade, or perhaps you meet a shipwright who inspired you and took you on as an apprentice? Do you own your own shipyard, in which you service others at your own pace, or are you simply a skilled laborer under someone else's employ? What drives you to continue to put your best foot forward on your work, do you seek the approval of a master, do you seek to prove your skill to the world, or do you just simply enjoy seeing ships the way they are supposed to be on the water? Regardless of how you got your start and your current working conditions, you still strive to see that the best quality vessels make it out to sea with your assistance.
Whenever you attempt to conceptualize a repair or an upgrade to a water vehicle that requires special materials, you know of said materials and where to find them, but dependent on the materials or what they will be used for, the DM may rule their rarity/difficulty when it comes to obtaining them. Additionally whenever you attempt to fix a water vehicle, make an upgrade or an addition, you have advantage on the ability check being made.