I'm not a master negotiator, but....

.....it strikes me that John Kerry could get the Maersk Tigris and its crew freed in about an hour if he simply noted that if the crew and ship are not freed quickly, there will be no lifting of sanctions and no agreement regarding its nuclear program, and that the U.S. will insist on full implementation of the nonproliferation treaty that Iran has signed.   If they balk, you blockade their ports and (a) don't allow them to export petroleum and (b) don't allow them to import gasoline. 

Kerry and Obama's inability to negotiate from a position of strength is a pathetic sight, to put it mildly.  God help them when they're in a position of weakness.