Lift Bag and SMB

Lift Bag or Dedicated Surface Marker Buoy?

Posted on Posted in scuba equipment

A surface marker and line is an essential part of a tech diver’s kit. Most people use either a lift bag or an SMB (surface marker buoy) as the marker. A reel or finger spool are two options for carrying and deploying line.

The reasons for carrying these items are many. If diving in a current, divers often deploy the marker, attached to the line, from depth and conduct their ascent while drifting. The marker on the surface lets the boat crew know where the divers are. It also gives divers a stable reference for the ascent. Divers can launch the marker if they get blown off the dive site unintentionally. Even if no current is present, divers can use the marker as a makeshift up line if they cannot find the proper ascent line. Besides using the lift bag or SMB to rig an ascent line, it can be used as an alternate buoyancy device in an emergency.

Lift Bag

A lift bag is usually a bag with an opening at the bottom. They come in various sizes, determined by how much lift they provide. The primary use of a lift bag is to lift heavy objects from the bottom to the surface. In the early days of technical diving, they were pressed into service as marker buoys for divers. The technique for deploying a lift bag as a surface marker is:

  • remove bag from storage space
  • remove reel from storage space
  • attach line from reel to lift bag
  • add air to lift bag
  • bag goes up to surface

There are several disadvantages to using a lift bag as your surface marker. First, lift bags are big and bulky. They take up space and can be hard to store. Next, if it is a model with an open bottom, it is susceptible to broaching. That is, the bag pops out of the water when it surfaces, air escapes through the open bottom, and it sinks back to the bottom. Lift bags also don’t ride very high out of the water, making them difficult for boat crews to spot.

Surface Marker Buoy (SMB)

Some SMBs are quite small, have no overpressure relief valve and are designed to be used only for signaling on the surface. These “safety sausages” are not suitable for our purposes as tech divers. I’m not referring to these “surface use only” models in this article. We are interested in SMBs that are specifically built for inflating at depth. They have overexpansion valves to vent expanding air during ascent. They are long and thin so that they stick up out of the water. SMBs are usually small enough to roll up and store in a dry suit pocket (even with a finger spool attached). SMBs usually have some sort of air trapping design so that once air goes in, it does come out until you let it out. This eliminates the broaching problem common with lift bags. The technique for deploying an SMB is:

  • remove SMB (with spool attached) from drysuit pocket
  • unroll SMB
  • add air to SMB
  • SMB goes to surface

Conclusion

Technical divers should carry either a lift bag or SMB to use as an impromptu ascent line, emergency marker, or back up flotation device. My choice is an SMB. I like using a piece of equipment designed to fulfill these purposes and not trying to make a piece of salvage equipment do jobs for which it wasn’t designed. I like that I can keep a spool attached to it¬†all the time. Also, the whole package fits in my dry suit pocket. It is out of the way, yet easy to deploy when I need it. Once removed from my pocket, I unroll it and inflate it. Simple. I don’t have to take time to attach the line to it and mess around. And once on the surface, I like that it sticks up out of the water three or four feet so the boat crew can find me.

I’m sure some divers disagree and prefer carrying a lift bag. That’s fine. Carry what you will. Whatever your preference, be sure to practice with it so that when you need it, you’ll be able to deploy it smoothly and quickly.

 

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