55 gallons of water weighs about 459 pounds. From an armchair engineering point of view, the maximum buoyancy provided will be the difference of that and the weight of the barrel.
Should you try to support that weight, the barrel will be completely submerged, and that the resulting forces may alter its size--reducing the buoyancy.
If you are planning any construction using plastic barrels as flotation devices, be certain you are in compliance with applicable laws and regulations--especially those regarding margins of safety.
Should you try to support that weight, the barrel will be completely submerged, and that the resulting forces may alter its size--reducing the buoyancy.
If you are planning any construction using plastic barrels as flotation devices, be certain you are in compliance with applicable laws and regulations--especially those regarding margins of safety.