If I needed a lawyer to interpret a contract before I joined a crew, I wouldn't want to join that crew.
I have only crewed on 2 boats, but each was after a discussion with the captains where we each discussed our experience, lifestyles, plans, and expectations. I turned down a third opportunity, when I didn't like the captain's boat, experience, plan, or ideas about expenses.
I kept my own passport, which I would be unwilling to surrender. I would lend it the captain to clear in and out of a country if I was not accompanying him to the office. I also provided several photocopies when they were requested bu marinas and authorities.
I paid my own travel to and from the vessels and split expenses for provisions, taxis, and paid for anything personal I bought. I didn't pay marina, cruising permit, or fuel fees or pay anything for transport. I did supply a lot of free labor on maintenance tasks beyond just sailing the boats. I am flexible and will provide return transport from any location, but that should be discussed. So if anything changes the final destination, the captain and the crew member don't get an unpleasant surprise.
I think, but can't prove, that if a captain were to demand that a crew member leave his vessel in a foreign port, that the crew member could claim that he was being stranded in that country and demand lodging and transportation to their home. So it is in the best interest of the captain to know that his crew has some financial resources and to keep a good relationship.
Spending time in a confined space with other people for any period of time can lead to conflicts. Throw in fatigue and discomfort and everybody better have the right kind of personality to get along. You can never be 100% certain about how you will get along with another person, but a legal document probably won't fix anything.
I am returning to one of the boats soon. I met the captain on this forum. We had several email and phone conversations before our first cruise. We never had anything in writing, but had a clear understanding of our roles.