Good fine

Your sailors only get 100% XP if you are driving a ship close to their level. If they are
ahead of the ship they get better XP than if they are behind. Your BO can't drive anything
above his level anyways, so for him that wont be a problem.

If you use lvl80 gunners in a CA they'll get rather poor XP. But don't worry. Their skills
make it a lot of fun to drive the CA. The most annoying thing will be, that the CA you can
drive has less slots than a BB3. So you need to kind of shuffle them sailors. And
depending on which ship you're talking about it could be an all lvl80 crew is too heavy
for it. If so I would try to save weight doing the shuffle in a way that includes the
radioman, so that you can eventually make more use of it. Just a thought though.

is the entire crew losing exp or just that pilot?

Hmmm... that's exactly what I used to think before getting that lvl 100 pilot into my CV xD

But thx for the info ^^

Ok, to my knowledge the other crew on your ship do not change exp amount. what
matters is the ship you are in, and that crew will be getting next to nothing in that
lvl 42 ship.

Exp will be 100% for the BO, more like 10% for the rest...