That would have been a different USS Gridley. Kerry's Gridley was DLG-21 (later redesignated CG-21). It was a Leahy-class guided missile frigate built in the early 1960's. There's no way could it have been the same ship your grandfather served on.
Kerry's boat, USS GRIDLEY, was on float with us in 1980, it is on this page.
http://rescueattempt.tripod.com/id5.html
Thanks, Bob. I appreciate the clarification. The Internet supplies very little information about USN ships, and I wasn't aware that the Navy recycled ship names (especially after only 15-20 years).
Cheers!
APf