I like the idea of not having just one "standard" of crew.Back in the day when a ship was short of crew they were garnered in several ways.
1."Removing" Crew from Merchant Vessels(Most of these would be accomplished Seamen)
2.The Infamous Press Gang(Mainly low grade Seamen if at all,most likely Landsmen.
3."Volounteers",either from Shoreside or from other ships,even Enemy ships(Most of these were seasoned seamen but of dubious quality especially if they came from another ship.)
So how would we "impliment this"?
Looking at Number one is simple,when you take a Merchantman or Warship there would be a certain Number of Seasoned Crew available to use.Their Quality would be fairly standard.
Number 2,When you dock in a port there is a Perecentage Chance of getting hold of Extra Crew of Varying Quality.Obviously Free Ports would also have the same % chance of obtaining Crew.This would be a small number,we arent talking Hundreds here but a dozen or score of Bodies.
Number 3.This mechanic could be one done on a Clan Level.You apply to the Clan for more Crew(these being trained Seamen)Also a random chance off the odd Volounteer would happen when Visiting ports.
There would need to be a system of "distribution" of Expert/Seasoned Crew between Gunnery,Sailing and Survival mechanics(Similar in the way we have crew management in a Battle Instance)The more Seasoned/Expert Crew you have the more of an impact on that ships ability to sail,fight and survive.Nations could have a randomly generated "arrival" of a Fleet which would enable Clans to receive replacements for Captains in their Clans.There also could be a mechanic for "training" up these Crew.
As a ship fights on,then the Crew would get more experienced(similar to the Officer you can recruit)Possibly you can accrue "Crew XP" which post Battle you can apply to crew to improve their Quality.
Just a few thoughts.