Liftbags are indispensable equipment during technical diving activities, where moderately large recoveries are expected. Although they are usually easy to use, divers should always be safety-conscious when using liftbags.
Using liftbags is easy and fun. Whether the liftbag is assisting a heavy bag of lobsters toward the surface or raising a treasure, advanced sport divers will enjoy the technology and challenge of using it.
“Technical” diving is the hot lingo used to describe activities that require specialized equipment, advanced planning and include working/calculating/using tools underwater. When you use physics principles to plan a lift, employ tools and knot tying and work on a project, you are a technical diver.
This article is limited to lifting small objects. If you plan to recover large or heavy objects like boats, that task falls into salvage diving and takes more extensive classroom and in-water training.
It is helpful to carry a small inflatable float and line in your BC pocket or goodie bag. Then, when you unexpectedly find a prize, you can inflate the float and mark the spot. This makes it easy to return to the shore or boat, plan the recovery and collect the necessary liftbags or tools. You may also need a lengthy surface interval to maximize your available no decompression bottom time and get a full scuba tank to provide sufficient air for the dive and the liftbag. When guiding an inflated liftbag to the surface, there is no pausing for a safety or decompression stop.
Table of Contents
The certification agencies’ specialty diving courses recommend recovering items weighing more than ten pounds with a liftbag instead of hand carrying them to the surface. The basic recovery equipment includes: liftbag(s), lines or straps, clips or carabineers, a large surface float and a cradle or basket for fragile items. Basic equipment does not include your personal BC or drysuit. It is not recommended to turn yourself into a human liftbag.
Liftbags are rated by the number of pounds of lift. Typical sport diving sizes are 10, 25, 30, 50, 75 and 100 pounds. Commercial applications (beyond the scope of this article and sport diving) use 500, 1,000, 2,500, 5,000 and 10,000 pound soft-sided sizes, plus rigid 55 gallon drums, alone or in combination. Liftbags come in several shapes, with the most common being hot air balloon and rectangular. The hot air balloon shapes have a large volume top and a narrow opening at the bottom. Woven nylon straps or lines are securely attached to the bag in such a way as to preserve the airtight integrity of the seams. Liftbags are typically manufactured from multi-ply vinyl, sometimes with fabric or strings embedded for extra strength. They are pliable and can be rolled up and carried by a diver to the site. The bigger the lift capacity, the bigger the bag volume.
The simplest liftbags consist of the bag and some way to attach a line. Air expands as the bag rises and fills the bag or overflows out the bottom. The only control is the amount of air blown into the bag at depth. If you are at 66 feet and fill the bag more than one-third, as the air expands it will bubble out the bottom. If you radically overfill the bag at depth, it will pick up speed on ascent, perhaps clearing the surface like a rocket. Sounds funny, until the inevitable crash, when the air dumps out and the bag and cargo drop like an anchor back to the bottom – hopefully missing you on the way down. If you tried to keep up with the runaway bag, you’d likely ascend substantially faster than 60 feet per minute and risk medical problems.
Makeshift liftbags, such as an inverted mesh goody bag lined with a heavy duty trash bag, will work in an emergency but have no dump valve and are prone to this runaway problem. It is tough to know how much air you have put in at depth. To control runaway bags, you need a dump valve to bleed off expanding air during ascent. There are two common dump valves. One is “automatic” and similar to the overpressure valve on your buoyancy compensator. The other is a manually operated hose with a spring valve at the end, similar to the manual deflation hose on a BC. Some liftbags come with both types of valves.
A hose with a manual valve allows fine tuning of the bag’s rate of ascent. By moving the hose higher or lower than the bag’s top and operating with short bursts or long releases of air, it is like using a car’s accelerator. You can speed up or slow down quickly or slowly, depending upon your “touch.” Practicing running a liftbag, so it responds perfectly to your touch, is fun and rewarding. Other equipment needed may include a separate air source. It is a judgment call. Typical divers, in shallow, calm water, lifting a light object and having a full scuba tank, will use their extra regulator second stages to put air into a liftbag. In deep, cold or turbulent water it is safer to use a separate air source to inflate the liftbag. A Spare Air bottle is easy to carry and operate for lighter lifts. Heavier objects could require a 50 or 72 cubic foot tank. The size of the air source depends upon the weight of the object being recovered, the lift needed to break suction with the bottom, factored with the chances of making the lift on the first try and the difficulty/distance of swimming for more air.
The rigging – lines, cords, straps and clips – that will be needed to attach the liftbag to the object varies with each recovery. Select lines that: are big enough in diameter to tie with gloved hands, don’t tangle easily, slip or float, are long enough for the job without joining pieces and will support the weight required. Nylon webbing (like mountain climbing line) is strong, easy to work with and, with clips attached, is quick and easy to use. The clips hook onto the liftbag harness at three or four points and provide a balanced attachment. Attaching lines or straps to an object, so it does not roll over or flip, can be tricky. It may not be easy to determine the balance point. For example, think of a small outboard engine. The engine part is small and heavy and the shaft is long, thin and lighter. The tendency, when recovering a small outboard, is to tie onto one place on the shaft, close to the engine. But, this is not the balance point. When you begin the lift, the outboard flips around so the prop is at the top and the engine is at the bottom. If you used short lengths of line to connect the liftbag, the prop slams into the bag, cutting it or dumping the air out. The bag and outboard drop to the bottom. A better procedure is to have multiple points of attachment and strive for balance. This often takes some creative rigging, since lost items don’t often have built-in attachment loops! When retrieving fragile items or several small ones, consider using a basket-like system. Having flipped a bucket of jade rocks that rained down on my buddy, this author likes baskets with lids. You can buy inexpensive plastic “milk crates” at hardware or office supply stores and make a wire mesh lid. One-half inch, heavy wire mesh, with silver tape folded on the edges (finishes the sharp edges) can be permanently zip-tied to one side of the crate. When you finish loading the crate at depth, use brass snaps on the remaining three sides to hook the lid to the crate. Everything stays trapped inside. The brass clips or carabineers can be snapped anyplace on the crate so they are easily accessible.
The four corners of the crate have easy places to attach liftbag lines. With three or four fixed points of attachment, the load is very balanced. Because the only solid part of the crate is the bottom, the water drains out when the crate is removed from the water.
In a pinch you could use a bucket, but be forewarned that plastic buckets with wire handles tend to pull apart and tip over. If you use a trash can, the weight of the water at the surface makes it very difficult to get the trash can into a small boat.
If you are swimming to shore, you’ll want to streamline the basket and use short lines in order to float the object as close to shore as possible. Pushing an inflated liftbag with a hanging basket or object at the surface can be very demanding. Don’t plan to swim far with a big liftbag and object.
Techniques And Procedures
Once you have attached a liftbag to an item, there is a tendency to want to rush to the surface. A little patience at this point goes a long way. First, be sure the water column above the liftbag is clear of divers. Second, use your air source sparingly to shoot short bursts of air into the liftbag. You are not filling the bag. If you are using your own air supply to inflate the liftbag, use your spare second stage. Leave your primary first stage in your mouth. Add only very small amounts of air at a time and then wait a few seconds to see what happens.
Your goal is to lift the object a few inches off the bottom and establish neutral buoyancy. Sometimes bottom muck has a suction effect on an object. It takes a little extra pull from the air bag or a push from a diver to break the suction. But, once free, all that extra lift will start moving toward the surface sooner than you want.
It is best to stabilize your buoyancy and the liftbag’s, just off the bottom. Check the rigging to see if the load is balanced, that knots have not come untied or lines have not slipped out of place. Pick up your tools and extra supplies so the buddy team can depart together.
To start an ascent, push the object up (not the liftbag). With a slight upward push, the liftbag will begin expanding and ascending. Add a short burst of air to the liftbag.
One diver should have control of the liftbag’s dump valve. The buddy swims on the opposite side of the lift, maintaining eye contact with the diver controlling the dump valve. Under no circumstances should anyone swim underneath a lift in progress! As the ascent continues, some air will probably need to be dumped to control the speed. Remember, you do not want to exceed the standard rate of ascent of 60 feet per minute, which is very slow – watch your smallest bubbles rise.
If the liftbag takes off too fast for you to make a safe swimming ascent, let it go. When you let a liftbag rocket to the surface unattended, swim at an angle, sideways, away from the bag’s path. Liftbags can breach the surface, flop over, dump their air and come crashing back to the bottom. You’ll want to be out of disaster’s path.
If, while controlling the slow ascent, you dump too much air, the contraption will reverse direction and begin to sink. Your choices are to use your octopus or alternate air tank and add a little more air, or let the liftbag settle, until it achieves neutral buoyancy or hits the bottom.
It is really tempting to take your regulator out of your mouth and quickly give the bag a burst of air. Don’t do it. That is an accident in the making. The bag is dropping, you are swimming up, the speed is out of control, you’ll have your regulator in between the lines – a recipe for entanglement! Let the liftbag fall. Follow it at a comfortable rate of descent. Once you catch up with the bag, check the lines and, when ready, begin the lift procedure again. Using tools and equipment underwater takes a measure of common sense and reading the environment. What is safe one day is not safe the next when the surge has picked up. The experience level of the divers, their tool handling and knot tying skills and mechanical ability will also affect the chances of success and safety of a planned recovery procedure. What works in 30 feet of clear water might be a terrible blunder in 60 feet of murky water. For example, in clear, shallow water. For example, in clear, shallow water, one diver may carry the spare scuba cylinder to the surface, while the other diver controls the lift. In arduous conditions, it may be prudent to leave the extra scuba cylinder on the bottom, marked with a float, while two divers guide the lift to the surface. During any recovery dive there is the possibility of bouncing up and down through the water column. Monitoring your depth, bottom time and surface intervals can be critical to avoiding decompression sickness. A dive computer is a valuable aid on this type of multi-level dive. After calculating bottom times for a repetitive dive or checking computers, the buddies may need to return to the bottom and retrieve tools and extra scuba cylinders.
Hopefully, you have planned how to get the recovered object into the boat with a winch or diver power, without giving anyone a hernia or dumping the object. As soon as practical, attach a safety line to the object and the boat for insurance.
Think through the relative weight/lift/volume of all components of a recovery operation. On another rock recovery project, several very experienced divers lifted a huge slab of slate, only to sink the rowboat once the slab was in it. Then the group put liftbags on the rowboat and raised it so the gunwales were barely below the surface. Diver kick-power pushed the boat back to the harbor. ‘Twas a long day but a grand entrance!
The simplest recoveries slip into the searcher’s pocket but, beyond these lightweight finds, using a liftbag is prudent diving practice. The diver’s safety must always be the primary concern.
Safety Rules For Sport Diving Recovery
* Always dive with a buddy.
* Always use a separate air source to fill the liftbag.
* Do not become a “human liftbag” by using BC or drysuit.
* Stay clear of the water column above and below a lift.
* If the lift goes out of control, let it go.
* Plan the recovery within the no decompression limits and allow for a multi-level dive.
* Prepare your equipment in advance with sizes and quantities appropriate for the job.
* If the lift is complicated, do an on-land walk-through so each diver knows his/her responsibilities before attempting them underwater.
* Murphy’s Law applies to all liftbag operations – if anything can go wrong, it will.