Chnaged submersible hull to Syldra-class and can't send on voyage?

[Angelhearth]

On our first airship we changed components one at a time, and continued sending it on voyages, but when I try to exchange a Shark-class hull for a Syldra-class hull, all voyage destinations are greyed out. The ship is rank 49, so there shouldn't be a problem. All parts, including the Shark-class hull, has been repaired. I have 59 Ceruleum tanks in my inventory. I can't figure out what I'm doing wrong here.