How Iran Attempts to Cloak Its Oil Exports

Via JPost:

Oil tankers departing from Iran have been "cloaking" their movements by turning off their global transponders, says Samir Madani who co-founded TankerTrackers with Lisa Ward.
   
Many tankers connected to the National Iranian Tanker Company have been spotted going into port but not coming out, Madani says. "Then you look at the export terminal with a satellite and see the tanker's no longer there."

    "Today, nearly the entire fleet [trading with Iran] is working in this manner in order to throw off the trackers."