Livyatan: What am I doing wrong?

Can't seem to beat the damn thing on my Aran with 85% Boss, 100% crit, 120% pdr and 240k-300k range buffed (with the MPE Red Pot, Echo and such, 300k range is with heroic memories + Terms and Conditions on). I always get him to like 10% hp left but then run out of time. DB in my alliance with half my Boss% and half my range can beat Livyatan. I've tried using the ship skills but those turned out to be useless for everything (at least the current level I have them).

What I've noticed is that he seems to have quite a lot of invi frames. I'm not even sure what Aran skill I should use for optimal DPS...