Well, the player above actually only burned experts to get his vets from 303 to 313. This seaman is a "special sailor" that you get from the medal shop. He comes at level 90 and if you level him up like that until 120 and only then class him Chief Seaman, he will automatically get 30% vets of his total crew size (303 vets of 1010 crew).

To your other question on engies as BO: mine is a late-classed one (level 116, classed 2nd engi at lvl 103) - he has still quite a bit of potential left. A normally classed engi would have a potential of 0 or thereabouts at that level, meaning, not useful as a BO.

You don't recall correctly.

ANY sailor of appropriate nation and level can be BO of an event ship. That was even established above in this thread.