The great shadow or the greatest frustration?

Tonight, i did 10 runs with randoms.
9 fails and 1 win with 1 minute left.

The causes are pretty simple: lack of knowledge and lack of gear.
How i play? Garuda6 with full piqure3, teuling, plague ward, front kegs, high velo kegs, potence, long gun works. Using a blightkeeper to manage debuffs. i think my gear is ok. I almost never die so i think i'm doing ok. Maybe like the others i miss knowledge to damage him more?

i tried looking for guides and info but all seem to say contradictory things.
Examples:
- don't kill the towers because they feed the shield
- kill the towers so they can't feed the shield
- just sit still and hit him. if he bubbles, rush him and do dmg inside is what i've been doing.

can anyone explain the full mechanics of that boss? is it bugged? i don't seem to expereince the same fight any time. Each time something feels off.

Here is my understanding:
He has a first phase that is a quick dps check. if that first bar is not downed very fast, it already shows that the party will struggle a lot. Hit weakpoints. Very easy.

Then he goes under and rises with things i don't understand:
- when inside one of his bubbles, he will pop the debuff at the end. Most of the time, i try to enter to dmg him and use rest kit if needed. He teleports around, signals a bit before sending his wave.
- when and why does he sail around again?
- we sometimes have a yellow light above us, what is that?
- what is the role of towers? (i know they send him a shield from time to time. Sometimes not a full shield. What triggers this? can it be avoided?) i had a run under 10 minutes where a player seemed to be killing towers all the time.
- why do sometimes the towers crush boats?
- why sometimes with a shield he gets his weakpoints exposed and damageable?
even when shielded he takes the piercing dmg. but sometimes, it takes crit dmg while shielded.

i'll take any info you can give :)
i suppose others players have no real clue too otherwise we wouldn't be failing so much.
Some players join with crazy low ships tho. Level11, under 300k infamy, snows, barques (can be great if one only and used properly), juggernauts... even saw a garuda with sea fire!