Pipe Pontoon How Wide (diameter) Do The Cylinders Need To Be?

How wide (diameter) do the cylinders need to be? - pipe pontoon

I am building a small pontoon boat to earn money, and I use PVC pipe as flotation devices for reporting. I do not know, should begin as wide (diameter) tubes to float and do not want to cut and then sank the boat, because too much weight. This information is necessary to solve (I think):

Although four cylinders 10 feet long is placed in water at a temperature of 0 degrees Celsius, and the four-connective bear weighing 800 pounds (1760 kg), the number of cylinders with a diameter of the final fleet because of weight?

Thank you in advance for anyone who can solve this problem!