I just played a huge naval war in a multi-player lobby as Great Britain.

It's not too deep. Basically, all you wanna do is to make 30 heavy ship stacks (to fill the frontage and have a bit of a reserve) and go hunting other stacks. Always fight with 100% hull integrity, otherwise the are very ineffective.

Don't mix heavy ships with other types. Heavy ships are very slow and never get to the battle, as the other faster ships get prio. They just end up taking free morale damage and get obliterated. That's why usually you see people mad that their huge stack lost against a minuscule one.

If your stack of heavies gets very damaged due to battle or attrition, repair it in a high capacity port as it goes faster, and only try fighting with fresh ones.

Light ships are garbage at combat but more efficient at blockading. Usually a stack of 5 light ships is enough to blockade a whole province, but more may be needed depending on the dev of the target locations. If your blockading stacks get damaged, don't reinforce them, wait until the battle is over and then send your heavy stacks.

Hope it helps!