Good question, Morgan. Actually, I know the
Cunard cruise line does regular transatlantic crossings on their Queen Mary 2 vessel, both westbound and eastbound.
Here's a schedule which includes to and from ports, it appears a typical trip lasts 6-8 days.
I also know a few cruise lines specialize in
world cruises. Since I'm on their page, the Cunard cruise line and their
Queen Elizabeth ship do world cruises, one of them being a monstrocity 90-day cruise that begins and ends in
New York. I'm sure other lines do these kind of excursions as well.
Are you thinking of taking a cruise around the world? If so then my hat's off to ya! Take lots of pics and let us know how it goes.