" I've been looking for similar information in the waters of the tropical islands. But have had no luck."

There is an interesting map in one of the classic survival texts, "The Survival Book", by Paul Nesbitt, Alonzo Pond, and William Allen, 1959. On page 11 is a diagram titled "Expected Time of Survival of Men Immersed in the Sea -February. They depict Area F - Indefinite (depends upon fatigue)- basically area F is everything between the Tropics of Cancer and Capricorn. Alaska falls into Area A-less than 3/4of an hour. Off coastal California (area D) survival is less than 6 hours. These times are for men in "ordinary clothing and a life preserver". They say nothing about those in the population with properly distributed fat....