109. Working dives

Once the surveying phase is complete, I will have a clear indication of the general layout of a site and I may even have picked up a few bottles already. Hazards will have been identified and marked. A complex site will have been sketched out on a slate.Wherever possible, the next step will be to lay a guideline so that I can work through the silt in my search for bottles. The general idea is to repeat each leg of the survey using the guideline, this time starting with the deepest leg and then gradually working shorewards. This technique is best suited for sites that follow a reasonably straight shoreline and are not disturbed by significant ridges, gulleys, or objects that could interfere with line laying. Many lakeside sites fit this category, but there are other sites that certainly do not, and in these circumstances special techniques are required which are covered elsewhere.

I prefer 8mm or 10mm polypropylene line. Polypropylene has a tendency to float, which is the sort of property I want it to have - I'd rather that the line be kept clear of the silt than sink into it. 8mm to 10mm of thickness is about right in my view... easy to find and follow with thick gloves on, but without being too bulky.

The line is secured at one end with a screw picket and by a weighted zipped toolbag or duffle bag at the other (see section 206, "How to make a line bag"). The line is sewn into the bag at the opposite end from the slider when the zip is closed. The other end of the line is tied on to the picket. The bag has two purposes. Firstly, it allows me to transport the line and picket to the site, and secondly it is a place to store finds. When transporting the bag, I will coil the line inside it with the picket projecting from the opening; the zip will then be closed against the neck of the picket. Once on site I can then unzip the bag slightly to about a quarter open, remove the picket, screw it in place (pushing it down in the silt so it bites), and lay the line by pulling it out carefully from the bag as I follow the correct heading. With the line spooled out, the bag can then be weighted down with rocks, bricks, or similar. At no point will I allow the line to lead me into, or close to, any hazard that represents a possible means of entrapment.

The length of the line will correspond to the length of each leg in the survey - i.e. 10 or 20 metres. The idea is to repeat the deepest leg first, following the line with the deep-side hand, while searching through the silt on the shoreward side with the other. When I reach the end, I will move the end point shorewards by one metre, maintaining tension on the line. Then I repeat the search as I turn around and follow the line back again, and then the other end will be shifted shorewards. This means that I am always between the line and the shore, regardless of the direction in which I am going.