Underwater lift bags are an essential tool in commercial diving, salvage operations, and subsea construction. They harness the power of buoyancy to raise, move, or stabilise objects that would otherwise be impossible to handle at depth. While the basic principle is simple, using air displacement to create lift. The types of lift bags available are varied, each designed for specific operational requirements.
In this guide, we explain the main types of underwater lift bags, how they differ, and where they are typically used.
Open-Bottom (Parachute-Style) Lift Bags
Open-bottom lift bags, often referred to as parachute bags, are among the most widely used designs. They have a cone or parachute-like shape and remain open at the base, allowing air to vent freely if the bag tilts or breaches the surface.
Typical features and uses:
- Suited for controlled lifting of heavy or awkward objects
- Equipped with dump valves for safe venting during ascent
- Common in salvage, offshore construction, and recovery operations
- Easy to handle, rig, and deflate after use
Examples in this category include Professional Underwater Lift Bags and Quad Underwater Lift Bags, which offer varying capacities and configurations for different project scales.
Enclosed Flotation Bags
Unlike parachute-style designs, enclosed flotation bags are sealed, meaning that once inflated, the air remains inside until actively vented. This makes them more stable and reliable when an object needs to remain buoyant on or near the surface.
Typical features and uses:
- Prevents accidental air loss during long-duration lifts
- Ideal for surface towing or stabilising equipment and structures
- Available in horizontal and vertical formats depending on lifting requirements
Specific examples include:
- Enclosed Flotation Bag – Horizontal: Designed to support loads evenly across a wider base.
- Enclosed Flotation Bag – Vertical (Salvage Pontoon – Vertical Cylinder): Better for narrow lifting spaces or when vertical orientation is needed.
- Professional Enclosed Underwater Lift Bags: Heavy-duty options for large-scale operations.
Salvage Pontoons
Salvage pontoons are a specialised form of enclosed flotation bag, designed for larger, more complex recovery tasks such as shipwreck salvage or large equipment recovery. They are engineered for maximum lift capacity and stability.
Key points:
- Available in both horizontal and vertical enclosed cylinder configurations
- Designed for use in shallow and deepwater salvage projects
- Built with reinforced materials for heavy-duty lifting
- Often deployed in multiples for lifting large vessels or subsea structures
Buoyancy Control Systems and Pipeline Floats
Not all lift bags are designed purely for recovery. Buoyancy control systems and pipeline floats are used to provide precise control over subsea installations. These tools help divers and engineers position, stabilise, or support subsea assets during construction or maintenance.
Uses include:
- Pipeline Floats: Used to support or float subsea cables and pipelines during installation.
- Buoyancy Control Systems: Provide fine-tuned buoyancy management for complex underwater projects.
These products are less about single heavy lifts and more about balance, positioning, and long-term stability.
Specialist Lift Bags
Several niche designs exist for unique subsea challenges:
- Propeller Underwater Lift Bag: Shaped for recovery or stabilisation of propellers, ensuring secure positioning without damage.
- Vehicle Recovery System: Designed specifically for lifting and recovering vehicles from underwater environments, providing tailored rigging points and stability.
- Rapid Recovery System (without cylinder): A streamlined solution for fast deployment when speed is essential, such as emergency recovery situations.
Choosing the Right Lift Bag
When selecting an underwater lift bag, the decision depends on several factors:
- Type of object being lifted (flat, cylindrical, delicate, irregular)
- Weight and size of the load
- Depth of operation and whether controlled ascent is required
- Duration of buoyancy needed (short lift vs long-term support)
- Safety considerations, including redundancy and venting control
For example, an open-bottom parachute bag might be perfect for recovering a heavy anchor, while an enclosed flotation bag would be better suited for keeping a pipeline afloat during installation.
Final Thoughts
Underwater lift bags come in many shapes and sizes, each tailored to specific subsea operations. From open-bottom parachute-style bags for general lifting to enclosed flotation pontoons for salvage, and specialist systems for vehicle recovery or pipeline work, the right choice depends on the project’s demands.
At iSubC, we supply a wide range of commercial-grade lift bags, designed to meet the highest safety standards and operational requirements. Whether you are planning a complex salvage, a construction project, or a precision lift, the right lift bag system can make the difference between a smooth operation and a challenging recovery.
