Now, don't take all this as gospel--because I know very little about it myself.
But in Moby Dick, it worked like this: The expedition was funded by a few wealthy men who came on the ship while it was at dock and arranged things, for instance making sure the provisions and supplies were all there. They even went out of the harbor with the ship, then took a boat back. The men--sailors like Ishmael--went to these men looking for work. The investors decided to take them on. I'm not sure the relationship between investor and captain, but I think they would roughly be partners.
The sailors would have gotten a share, sometimes very small. I can't remember the actual amount, but Ishmael's take was something like 1/200 of the profit from the voyagel.
So, yeah. That's all I have. And I got it from Moby Dick, lol. Herman Melville DID go whaling, though, so he knew what he was talking about.