Carter Bag Boatlift Tubes are usually used in pairs to make it easy to remove Boatlifts from lakes in the Fall to prevent them from being damaged by ice and easy to replace them in the Spring when the ice melts. They can be filled with any air compressor and require only about 3 psi to pop off the overpressure valve. They can also be used in deep water for other types of underwater lifting. For very heavy Boatlifts  is may be easier to use (4) CBEP-500 lb Pillow Bags.