"So let's say he came out of his boat in it...would he stay up or would it pull him down?"

Based on watching an unnamed fellow paddler take a nasty swim in a whirlpool in the Pembroke Reversing Falls in Cobskook Bay this summer his PFD did not keep him afloat. He let go of his boat for a second and spent several seconds (probably felt a lot longer to the swimmer) under water. He was able to grab his boat which provided enough flotation to keep him above water. The lesson learned was never let go of your boat!

A group of us actually ran into the Bryan Smith (the film maker) at the Canadian border in Lubec, ME in 2009 as he was heading up to meet Paul Kuthe to film paddling in the St. John Reversing Falls. Some of the clips in the video are from Bryan's "Eastern Horizons" DVD.