Really once you've lost navy you've lost navy. Once you lose your options for getting back in the water are incredibly inneficient; if they weren't there'd be no point to early aggression. The key is to scout and know what your opponent is doing. If you are playing against aggressive players (that you think will push you hard at t2) you should avoid UEF.
Fatboy vs. Navy is one of the things I see new players do a lot that is just awful. It has battleship DPS, shit HP, and costs 4x more. If you have that much mass and you've lost navy you're better off putting mass into alternative eco sources like massfabs and RAS SACUs than into a useless fatboy.