No one is required to render aid, including the Coast Guard, BUT it's very nice if you do.
Check out AMVER.
SOLAS 1974
Regulation 33
Distress Messages: Obligations and Procedures
1 The master of a ship at sea which is in a position to be able to provide assistance on receiving a signal from any source that persons are in distress at sea, is bound to proceed with all speed to their assistance, if possible informing them or the search and rescue service that the ship is doing so. If the ship receiving the distress alert is unable or, in the special circumstances of the case, considers it unreasonable or unnecessary to proceed to their
assistance, the master must enter in the log-book the reason for failing to proceed to the
assistance of the person in distress, taking into account the recommendation of the
Organization, to inform the appropriate search and rescue service accordingly.
2 The master of the ship in distress or the search and rescue service concerned, after
consultation, so far as may be possible, with the masters of ships which answer the distress
alert, has the right to requisition one or more of those ships as the master of the ship in
distress or the search and rescue service considers best able to render assistance, and it shall
be the duty of the master or masters of the ship or ships requisitioned to comply with the
requisition by continuing to proceed with al speed to the assistance of persons in distress.
3 Masters of ships shall be released from the obligation imposed by paragraph 1 on
learning that their ships have not been requisitioned and that one or more other ships have
been requisitioned and are complying with the requisition. This decision shall, if possible be
communicated to the other requisitioned ships and to the search and rescue service.
4 The master of a ship shall be released from the obligation imposed by paragraph 1
and, if his ship has been requisitioned, from the obligation imposed by paragraph 2 no being
informed by the persons in distress or by the search and rescue service or by the master of
another ship which has reached such persons that assistance is no longer necessary.
5 The provisions of this regulation do not prejudice the International Convention for the
Unification of Certain Rules with regard to Assistance and Salvage at Sea, signed at Brussels
on 23 September 1910, particularly the obligation to render assistance imposed by article 11
of that Convention