RE: pop bottles as floats?
And puts the main point of contact with the water at take-off speeds slightly in front of the CG so that the airplane can rotate for take-off. Notice that the main bottles on John Bruckner's Kerswap are located so that the rear of the bottles is either in front of, or under the CG. The back of the bottles acts as the step, but with no floatation behind the CG, the third bottle is necessary to keep the tail out of the water.
Jim