Personally, as a GM, I'll let any PC plan work. The caveat being, there has to be a plan.
If the players just walk into a conflict, they're gonna get slapped silly. If they they can come up with something reasonably intelligent, I'll let it work.
Heck, in a fantasy game, I had a player tie together a couple of boats and, using canvas and paint, build a sea monster to frighten the opposition. The fact that he was colour blind just meant that the enemy were facing a paisley patterned sea monster. I still let it work, to the extent they were distracted enough for the other players to successfully attack from the flank.
So, stealing a ship ought to be impossible. If the players can come up with some way around the impossibilities, let 'em have the ship.
OTOH, make the theft easy but give them some major consequences, like the crime boss someone mentioned above.