Your immigration research is not done simply because you found your ancestor's name on a passenger list. You also want to get some information about the ship on which he or she traveled. Actually seeing a picture of it and reading about its voyages can give you an idea of the experience your ancestor had.
You can find ship references at the Ship Index website. It tells you which books, magazines, and online resources mention the vessels you're researching. With 142,804 entries in the free database and 1,420,968 entries available with premium access, you're bound to find useful information there. Given that part of the site is closed unless you subscribe, you might run into a dead end occasionally, but it is worth the hunt. Remember, this site gives the primarily references to go look at, not the information itself.
Check it out at http://shipindex.org/