I did in fact forget changing outfits unequips the shell, but corrected that posthaste. Now after, hell, what feels like 60+ actions of aimless meandering I suddenly got 3 Jellyfish in rapid succession. Either they actually upped the jellyfish drop rate, or the RNG decided to have mercy on me.
The Abyss awaits.
Edit: CONFOUND IT, if only it were legal to drink Hesperidean Cider while zailing…
Edit 2: Bless the Pillared Sea offering you the opportunity to capsize your own ship. There is something fundamentally wrong with the idea of drowning to optimise your action efficiency, but I have taken full advantage of this mysterious Treachery.