Underwater Lift Bags

Underwater lift bags are used to raise, move, or stabilize submerged objects during marine salvage, construction, and recovery operations.

Underwater lift bags are secured to a load and inflated with compressed air. As the bag fills, it displaces water and generates upward force. The total lift produced depends on the bag’s volume and the surrounding water conditions. This controlled buoyancy allows divers to safely raise, position, or stabilize objects underwater.

The main types are marine salvage pillows, enclosed lift bags, open bottom lift bags, pontoon lift bags, and convertible salvage bags.

Each type is designed for specific underwater applications. Enclosed lift bags are often used for controlled lifting and stabilization. Open bottom lift bags are commonly used for deeper water lifting where air expansion must be managed. Pontoon lift bags are used for shallow water flotation and towing support. Convertible salvage bags offer flexibility by functioning in more than one lifting configuration depending on project needs. If you want to explore these options in more detail, see our guide to underwater lift bag types and applications.

Open bottom lift bags are designed for deeper water applications where air expansion must be safely released as the load rises. Enclosed lift bags are sealed and provide more precise buoyancy control, making them ideal for stabilization and controlled lifting in marine construction and recovery.

The lifting capacity of an underwater lift bag is based on the amount of water it displaces. Larger bags generate more buoyant force and can lift heavier loads. Multiple lift bags can also be used together to increase total lifting capacity and improve stability. Proper load calculations are essential for safe operation.

Underwater lift bags are rigged using slings, shackles, or lifting points attached securely to the load.

Proper rigging ensures even load distribution and stable lifting. Connection points should be strong, balanced, and appropriate for the load shape. In many cases, multiple attachment points are used to prevent shifting during ascent and improve overall control.

Capacity ratings reflect maximum buoyant lift, while actual performance depends on conditions such as depth, rigging, and load balance.

An underwater lift bag’s rated capacity is based on ideal conditions. In real-world applications, factors like depth, load distribution, and environmental conditions can affect performance. Proper planning and setup help ensure the lift meets operational requirements.

Select lift bags by required lift capacity, water depth or operating pressure, available clearance, attachment points, inflation method, and whether the load must be lifted vertically, stabilized, or moved horizontally.

Use an appropriate design and rigging safety factor, inspect the bag and hardware before use, control inflation, keep personnel clear of the load path, and follow the manufacturer's instructions for inflation pressure, attachment, and capacity.