Ok thanks for the advice.
I'm using the BO with AA gunners and now i have 100 experts. I'll continue use AA and
try to get some vets and wait to a new event to boost my BO.

Like it's been said above, it's because your BOs don't have enough ability. You can fix
this by either adding experts, adding vets, or getting him boosted.

One thing: be careful not to overexpert your BO, try to get your ability out of the vets.
The reason why is that ideally you'd like your sightlines to exactly equal the range of
your shells. At higher levels, you'll need to pull recruits off to shorten the lines. If you
have too many experts that limits the amount of recruits you can pull. So you are
forced to burn experts (i.e. try to convert them to vets to kill them off). Can be
expensive. So keep space for at least 100 recruits always.

Ok thanks Raptor.

The Potential true ability of the BOs isn't quite high enough to mark the shells. Some
more vets on either (and some more experts for the BB BO) and they'll be able to spot them.

I'm doing something wrong with my calculations, so I can't give you exact numbers, but if
the BB (level 67) BO gets 40 more vets and 100 more experts, that *should* be enough. (He
has ~1000 displayed Potential, right?)

You can also check Adalbert's guide for details on how much ability is needed. Note that
one can spot shells at least 3 (maybe slightly more) ticks beyond the end of the guidelines.

Ask lordrevan or verfallen or facepalm, they should help you better than us.

14 (BO CV)
13 (BO BB)

I did a test now.
With Aiming FCS the shells disappear.
With Auto and Finder the shells dont disappear.

Hm. Vet count's a bit low on both, and the experts are rather short on the level 67 BO.
What base(s) are they?

My level 67 BO have:
429 Recruits/6 Experts/60 Veterans

My level 86 BO have:
269 Recruits/300 Experts/70 Veterans

Sounds like you have the right FCS.

Could you post screenshots of your BOs? They may be short on experts/vets. And yes, this
would most likely happen with the Yamato when you first get it -- while it does have a
better FCS, the guns are substantially longer ranged.