Hi Russ,
The Fenix P1D-CE is IPX-8 rated according to the manufacturers website.
http://www.fenixlight.com/viewproduct.asp?id=35IPX-8 -'Protected against water submersion - The equipment is suitable for continual submersion in water under conditions which are identified by the manufacturer.'
IPX-8 has to be greater than IPX-7, which means that it has to be at least 1m depth for at least 30 minutes or greater.
Its certainly not a SCUBA flashlight but would be perfectly useable at the surface to be used for improvised signalling.
If I was going to sea, I'd go with dedicated gear designed to get real wet, dunkable is fine for non-survival gear, not for gear your life hangs on.
PPPPPP, definitely!!