Always when off the hook
The boat rule is: Lifejackets are mandatory when off the hook anytime you are in the cockpit or on deck. Doesn't matter if it total glass and no wind or 100 deg F. We have automatic inflatables for all our guests and none of them has ever complained about wearing them. When I go out alone, I wear a auto-PFD and tether.
The water here is cold; never really getting above 70, and most of the time it is the low 60's and less. In the event a person goes over, I am more concerned with them getting cold and not being able to move, hence the PFD to keep them afloat. Also, if they are hurt or unconscious and can't keep a float, the PFD will.
Since I am in charge of their safety aboard, a PFD is a inexpensive piece of equipment that reduces the potential of for a fatal incident.
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