What is a Derbyshire Tube please?
Pete's reply is quite correct but a bit more detail might be helpful. It's a line laying device based on a scaffold tube which was invented originally for difficult underwater terrain. The idea is you pull out loops of line from under the inner tube loops as you progress. But if things get nasty and you want to run away you just drop the Derbyshire tube and retreat. There's no faffing around trying to find a belay, attach the line, cut the reel off and secure the remaining line on the reel, all in fast deteriorating vis. The scaff tube is negatively buoyant so it just sits of the floor and when you go back you return to a safe situation (no loose line floating around). Once all line is laid the empty scaff tube can be rammed into a sediment bank to further secure it (in the manner of the cave diver's plastic pipe "silt screw") or simply placed on the floor of the sump instead of using up a lead drop weight. It can also be used as a "squeeze gauge" in a wide, low bedding to identify the highest part of the passage and follow the best traectory.
The photo below shows how I make them. Points to note are:
1 The line is marked every metre, which makes surveying awkward passages easier / more accurate.
2. The overall length of line on it is labelled at the starting loop. This allows you to pick up the correct one from a box of several previously made Derbyshire tubes before diving and also helps identiify the correct loop to pull out first before looping the device onto the end of the previously laid line.
3. The extra loop of white string to the right in the picture below is so that the device can be secured to the existing line partway along if you want to leave it in the sump and fastened with a loose cable tie (which is then cut on a subsequent dive when the Derbyshire tube is collected).
4. The extra inner tube stretched over each end for double scurity; the last thing you want to happen is a failure of a single snoopy allowing line to be spilled. This also helps keep the loops of line stacked more tidily.
5. What isn't clear from the photo is the advisability of transporting the Derbyshire tube into the sump in an SRT bag, to avoid the possibility of accidentally pulling coils out before intended deployment (i.e. if it gets snagged en route in).
They're not
just for low visibillity situations. The one in this picture was laid in 20 m vis (not a misprint!) in Austwick Beck Head on Wednesday just gone. The reason for choosing this, rather than a reel, was because the area of the cave in question was right at the limit of the available cylinders. The Derbyshire tube could be emptied fast, surveyed back quickly and then head straight for home.
There you go braveduck; I bet you're really glad you asked!
By the way, the "silt screw" referred to above was a Scoff invention. The Derbyshire tube was invented by yours truly.
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