The American Osprey is one of five tankers fired with an Offshore Petroleum Distribution System. The five tankers belong to the U.S. Maritime Administration (note the red, white and blue stripes on the stack). All five are maintained either in the reserve fleet, or deployed overseas as pre-postion ships. This article about the Petersburg, one of the other tankers equipped with an OPDS, explains how the equipment works:
https://maritime.dot.gov/multimedia/ss-petersburg-t-aot-9101

In this article ( https://www.navsource.org/archives/09/65/pdf/655075a.pdf ) it's explained what it was and how it works

Looks to me like an barge type floating device which can be released quickly from the deck of the tanker.

http://www.navsource.org/archives/09/65/655075.htm

https://cdn.dvidshub.net/media/thumbs/photos/1909/5761141/1000x667_q95.jpg

On deck is something she did not carry when trading as Gulfprince, but I have no idea what I am looking at.