I would also suggest getting a SART and an EPIRB. A SART is a radar beacon, which shows up as a distinctive pattern on surrounding ships' radar displays, and requires no special receiving equipment. An EPIRB is a beacon that is locatable by satellite, so that's the fastest and most reliable way to get the attention of a rescue control centre. These three technologies are part of the GMDSS (Global Maritime Distress and Safety System), which means commercial ships and emergency services are by law required to carry and use equipment to receive their signals.