anything more than a 1-2 ft max swell would probably kill the floating... if the water temp is swimmable, and little swells, and the person is in decent shape, i believe more people than you think could make 9 miles... they might swim 9miles in a circle because they couldnt see land to know where to go, but i think the mind and body can do some incredible things when death is thrown at you... but you would need to be in decent shape to give it a chance... im in good enough shape and have enough swimming and floating experience to make it 9 miles in water warm enough to swim in and with small swells...
saulty and his 50k calorie guesstimation is off by probably 35k for a guy his size .. he is off by around 40k or more if the 9miles is done in a pool