Originally Posted by UserName
As I recall, a test from underwritters lab... 95% public weigh between 14 & 15.5 lbs in the water (under water?). So past the weight of skin & Bones alot of what a person is made up of is either neutral or negative boyancy (75%ish water essentially)
So these figures are from trying to remember many many years ago, and are probably not exactly accurate, but this is the concept / theory / resoning...
A Pfd only has to float more than 15 lbs to make you possitively boyant. Certain situations any more boyancy can be a problem (recirced in a hole, etc.) A lot of people feel high float pfd's are most suited to High Volume Rivers (Grand Canyon etc.) while lower float is just fine if not better for rivers such as in colorado; lower volume... Lower profile of pfd is also a valid consideration beside just comfort.
So there you go. How much do you weigh in the water? Can your friend pick you up in the water? On land?....
I am no expert on flotation and PFD's, but I think what the previous poster is saying makes sense. A stocky, muscular 125lb person will have a harder time floating in water than a 275lb, shall we say less muscular person. That being said, I assume the testing each PFD undergoes to get certified would factor in different body weights, shapes, etc. and the floatation is safe for all variables. That maybe a wrong assumption though.
I would also like to hear peoples opinion on high float (over 20lbs) and standard 16lbs or so PFD's. Do you think the floatation should change if you are kayaking vs. rafting?