@el-glaude
Hi, late to the party here !
i will give all kind of advice i can think of.
1- crew organisation
the crew goes by, Hellmsman, Bilge, Cannoneer and Boarder.
each role should have a canon assigned, i will go from back to front.
Canon 1: Should go to the helmsman since it's closer to the wheel, so he does not have to run to the front of the ship shoot 1 ball and then ruch back to the wheel because it does not have more time to shoot.
Canon 2: Should go to bilge, so he can easely backtrack below deck and repair.
Canon 3: Should go to the canoner sinc it's role is versatile, it's best for him to be around the midle.
Canon 4: should go to the boarder, since it's the most forward and so, the best place to launch yourself in front of ships.
Also, having a set canon prevent any "floating time", where your crew after realoading their cannonball would jump on a canon, only to realise their took the same canon and one has to change.
Supply accesybility:
it's important to grant easy access to supply at key point on the ship. Near the canon line usealy behind the anchor (not on it ! you pitiful sweaty f*k), below deck for easier repairs, near the wheels so the helmsman can stay glue to it, and more specific point like in the middle deck, or ammo box near the ladder and at the back and front of the ship.
the idea being, to kill any downtime of your crew reloading, the more time putting pressure the better !
Hellmsman:
it's my main role so i have a lot to say; first off, all your crew should have experience at helm, wether it's to be able to replace you while you go back from the ferry or the merm, or simply to better understand the way a gally navigate to better help you at sail management.
It's important to realise that anything on a gally takes a ton of time, so you really need to be sure of your actions, i highly recomend to stay at all time around the wheel to be able to react as soon as possible, if your not turning the wheel, keep watch on ladders to catch sneaky boarder ( personaly i use snipe pistol so i d'ont have to run after the guy with the sword) or watch how acurate your volley of canonball is, tell your crew if it's too high or too low, finally snipe the enemy crew/ helmsman, especially if you have an ammo box, whith that you will be able to put pressure, and when you hit some nasty shot, it feels really good ! and then, you can work on back and middle sail if need be.
Sail management ! understand that the galion as the most variable when it comes to speed, wind is your enemy if you catch it on a broadside you will have to reposition, especially if, you catch the wind on all 3 sails !
to prevent that i usally make sure, only 1 sail can catch wind, middle sail is facing the front, the front sail is facing away from the wind (either left or right not full left or full right, so it does not take ages to move them, with this the crew can stay focus on cannon fire), and the back sail is near the wind or against, since i can quickly access it.
Most of the time you will raise the middle sail, for better mobilyty and visibility, but their will be times when it's necessary to have all 3 sail down to match speed etc.
Always be mindfull when you have to raise them.
The N*1 rule: SAILS management is above firing a canon, your priority is to get as fast as possible set up, so then ! you can shred the enemy.
Patience is key, if you need more mobility you can raise the front sail to half, it's also very comon to raise front and middle all the way to get a boost movement before droping the front sail.
another tip: if you want to turn faster, but whitout slowing down by raising sail, angle the sail against wind (it's obvious but still), and keep them against wind as you turn, take notes of wave too, they can help you get a broad or hinder your actions.
Last crucial tip: Ingage in broad as far away as possible.
the more far away you engage, the more big the angle is, and the easier it is to keep said angle. galion really struggle at close range, sure they can destroy you if you get caught in broad, but as a gally crew wining because the other crew made a mistake, is no fun, the fun comes when you are a well oiled crew, and all your actions where clean and perfectly executed, leaving the other ship utterly destroyed.
to be simple at close range the gally become a dog chasing it's tail.
so yeah, as you probably guessed, you need to train your crew at long range, sail around target a fort tower or a rock and do a broad on it.
also comunication, if one of your crew hit the ship have him help the others.
things like "aime for the crows nest" "aim the fat cloud" etc.
that way, even if your crew sucks at canon aim, if one is able to lock, all will follow.
resulting in other crew sh*tting themselves, because once your an artillery galion, your crew trulu becomes op.
there is more stuff but i'm lazy ^^ figure out the rest, have fun with your crew, see it grow in skill, that's the best experience in sea of thieves.