I have just completed a course and been awarded a Marine Radio Operators Certificate of Proficiency (a requirement for using both VHF and HF here). The extensive 130 page handbook issued by the Australian Maritime College which is based on the International Radio Regulations contains the following:
"56.2 The [Mayday] signal indicates that the vessel or person using it is threatened by grave and imminent danger and requests immediate assistance."
Note the reference to "vessel or person using it".
"56.3 The distress signal must not be used under any other circumstances"
"56.4 It should be noted that the use of the distress signal is only justified if the vessel or person using it is threatened by grave and imminent danger. It does not extend to situations where immediate assistance is sought on behalf of a person, for example, a medical emergency. The urgency signal should be used in these situations"
Therefore, if a person falls overboard, and it is not the person using the vessel, then it is clear that the Mayday call is NOT appropriate.
The handbook describes the use of the urgency signal (Pan Pan) as follows:
"67.2 Use of the urgency signal indicates that the station sending it has a very urgent message to transmit concerning the safety of a vessel, aircraft, or person."
Section 66 describes the situation "Transmission of a Distress Message by a Station not itself in Distress", including where the vessel in distress cannot transmit, or where further help is necessary (eg where you arrive on scene and need more help), or where you hear a Mayday that has not been acknowledged. In all these cases the signal "MAYDAY RELAY" is used.
Marine Radio protocols are of an International standard and apply everywhere.
Hope this helps
(No worries mate!)
Western Port Marina
Hastings, Vic, Australia