Actually, at equatorial water temperatures, say, 25deg. C and above, in saltwater, a body , if it sinks at all, can surface in less than 24 hours. Depends on exact temp, body fat, clothing, completeness of the remains, salinity. Water temp is the most important factor for 2 reasons. As water warms, at least above 0C, it expands, reducing its density. Also, warmth accelerates decomp and the attendant release of gasses.