206. Making a line bag

The use of line is fundamental to most branches of technical diving, and bottle diving is no different. Once underwater it is easy to become disoriented and the presence of a line provides reassurance and a sense of direction. Most usefully, it allows the diver to make progress entirely by feel...an important consideration in silt-out conditions.

Without some sort of line a bottle diver would be restricted to high-level surveys and the occasional rummage. With a well-laid line across a previously surveyed and risk assessed area, a bottle diver can grope bottom to his heart's content, secure in the knowledge that the line provides a safe point of reference even in zero visibility.

In my experience the best way to manage line is with a line bag. This is a small nylon duffle bag. The line is sewn into it at one end and tied to a screw picket at the other. When deployed the line marks the leg of a dive, and the diver can progress along it searching for bottles.

Here's how to make one:

Step 1) Assemble the pieces (see illustration, top left). You'll need a screw picket, about 10 metres of 8mm or 10mm polypropylene line, and a small nylon holdall or duffle bag. You'll also require a needle and some nylon thread. Identify the "near" end of the bag - this is the end next to the slide of the zipper when the bag is closed. The "far" end of the bag is of course the other end - i.e. the end closest to the slider when the zip is open.

Step 2) Sew one end of the line into the bag at the "far" end (see illustration, right). Use nylon thread rather than cotton, since it will last longer underwater.

Step 3) Tie the other end of the line to the picket (see illustration, below left). It is essential that the picket should be allowed to rotate freely. If the picket has a suitable link for tethering then use that; tie it with a fisherman's bend or a round turn and two half hitches. Otherwise tie a bowline around the shaft of the picket, not so tight that the picket can't rotate inside, and not so loose that the bowline slips down the screw.

Step 4) With the line coiled inside the bag, the zipper can be closed against the picket with the picket handle sticking out (see illustration, below centre). This is the easiest way to transport a line bag.

In use, the bag should be unzipped slightly to allow the picket to be removed, then the zipper should be refastened against the line (see illustration, below right). By screwing the picket into the silt and finning away parallel to shore, the line will pay out of the bag until the end is reached. The bag can then be weighted down with stones. The line, which should be kept as taut as possible, then marks the first leg of a working dive.