46 CFR 4.04-1: -1 Reports of potential casualty.

(a) An owner, charterer, managing operator, or agent of a vessel, floating OCS facility, or MODU to which this part applies must immediately notify either of the following Coast Guard officers if there is reason to believe the vessel, floating OCS facility, or MODU is lost or imperiled:

(1) The Coast Guard district rescue coordination center (RCC) cognizant over the area the vessel, floating OCS facility, or MODU was last operating; or

(2) The Coast Guard search and rescue authority nearest to where the vessel, floating OCS facility, or MODU was last operating.

(b) Reasons for belief that a vessel, floating OCS facility, or MODU is in distress include, but are not limited to, lack of communication with or nonappearance of the vessel, floating OCS facility, or MODU.