It's called naval positioning, your ships stacks must not be bigger than 50 and don't ever put them in the same battle.
Not realy, actualy you need to have less than 100 cannons for 1% of positioning, meaning, you need to have 5000 cannons for 50% positioning... but is more complicated, as best would be 6666 cannons for 50% as they bring same fire rate with more hull. But, on the other hand, not in every battle you get 50% positioning, so, i think it is best to have around 6000 cannons to be more optimal in case you have less positioning. Also for big fleets it is good to have good maneuver admiral. In most situations i had, i got around 30-40% positioning. Anyway, allways try to get fleet NOT bigger than 6666 cannons, as it will never be effective. Just try to keep it around 4k-6k cannons. And try to calculate cannons... allways. Also try to get as much hull as you can if you want to destroy enemy fleet, and as much ship speed as you can IF you want to capture enemy ships - as when enemy fleet flee - at least i think so - you catch as much ships as your fast ship allow you to.
EDIT: For example Carracks, have same hull as cog but cog got 10 cannons, and carrack got 40.
So technically, you get more powerfull fleet from building cogs, BUT it MAY cost you more actualy(unless you got realy big support limit). You will need 500-600 cogs to build a superior fleet, and 125-150 carracks to make same firepower fleet. Same galley fleet (500-600 galleys) will also be superior, but will have less hull (but higher speed).
It is like - transport ships have allways twice hull it got cannons, and big ships will got double the cannons they got hull. So if you plan to have big hull but not too much ships, add quite much but not too much transports. It will give you two things - good hull, and less fleet maintnance.
EDIT2: Could some mod move it to new thread, as it goes offtopic?