One of the inherent problems with the throw bag is that the weight necessary for effectively throwing the bag comes from the rope in the bag itself. If you throw it and miss, you must quickly retrieve the rope, but because time is critical, you will probably not be able to take the time to stuff the rope back in the bag for another throw. A good technique is to retrieve the rope with both hands, piling it between your legs. If you have a bucket, pail, or basket, you can pile the rope in there. This way, it is in a compact form and ready to throw again. Some rescue instructors recommend looping the rope around your hand to keep it from getting tangled. As you practice and prepare to perform rescues, you will learn the technique that works best for you. Your technique choice may also vary with the circumstances of the rescue (time, distance, wind, equipment, and so on).
Because the bag has no inherent weight and you won’t have time to stuff the rope back in, a good idea is to quickly fill the empty bag with water to replace the weight of the rope for another throw. You’ll have to do this quickly because the water is likely to drain out if you delay. I know it sounds obvious, but make sure you or someone else has a secure hold on the end of the rescue rope so that you don’t lose control of it while concentrating on getting one end to the diver in distress. During training people often watch the throw bag or life ring sail perfectly beyond their intended mark only to watch in horror as the end of the rope also sails into the water because they forgot to hold on to the end.
Although a throw bag is easier to throw than a life ring, a life ring provides buoyancy for the diver(s) in the water. In a pinch, you can use any float tied to a rope. Throw the float or life ring sideways with a forehand motion, or toss it underhand as if pitching a softball. You should aim for it to land just beyond the diver so that you can pull it back to the diver.
Your decision of which device to use will depend on what you have available and how far the injured diver is from the boat, dock, or shore. Typically, throw bags allow you to reach a greater distance, but they do not give the diver any additional buoyancy. The float or the life ring is harder to throw for any distance, but it gives the diver additional support.
Regardless of which device you use, pull the line slowly and continuously. Rescuers in the water should encourage the conscious diver to grab and hold on to the line firmly. If the diver is unconscious, the rescuer should grab the line with one hand and the diver with the other, and allow surface personnel to tow them both in. Throwing a life ring or throw bag may seem simple, but proper training and frequent practice is essential.
This is an excerpt from Scuba Diving Safety.