Hi Gang, PDFs are mandatory, as are tethers when things start to get dicey; but other safety bits are needed as well. PDF's alone are good but need further safety equipment. In addition to your PDF, once you are in the water; how loudly can you yell...?  ...and for how long?  What is needed for each of your on-board PDFs is an attached whistle, that is a lot louder than your voice, and requires less energy to keep blowing it. Another item - if you are out at night - should be a water-activated flashing light attached to your PDF.  They don't cost much; but make locating someone; or you, in the water a lot easier. Connie