The Tank

The tank is an ex-water tank that is inverted and filled with air at a depth of 12m and is one of the only tanks in this country that is still operational. It was constructed over the winter of 1985/86 but in July 1986 had to be sunk in the reservoir before it was completely finished due to the lack of storage space. It sank on its side and was not righted until August 1987. It remained in an unused state for several years before being moved to its present position in 1990.

Inverted Tank being taken into position.

Blocks lowered from lorry. Dave Parham left.

Block being put onto the inflatable.

Block being sunk near the jetty.

The Problem... Keeping it on the bottom

As the tank was to contain air it had to be held down, its size was around 1.6m square by 400 mm deep giving a displacement of about a ton of water, this required some big weights to hold it in place.

The work begins... Off the back of a lorry

Eventually the club came across some 'L' shaped concrete blocks each weighing well over a ton out of water. The blocks were lowered onto an old inflatable from the wagon on the slip, then floated out and the inflatable let down until the blocks slipped off. During the following weeks four of the blocks were moved near to the tank using conventional lifting bags and barrels.

Working with the Blocks

The blocks were needed in an inverted 'V' fashion to hold the structure to the bottom but all were on the bottom on their back. The correct procedures were found with much trial an error to both turn them over and place them accurately. This was the project that changed our whole method of working with heavy objects underwater.

Oops!

We had tried lifting bags in many different ways but all proved dangerous, with the bags hitting the surface deflating and a ton, or so, of concrete hurtling back down to the bottom, one came so close to my buddy it displaced his mask and took a fin clean off!. The method we eventually used was with a chain winch hooked onto a '1-ton' sand bag filled with 3 x 200 litre barrels permanently floating on the surface. This was insufficient to lift the blocks but would give a very controllable addition to the other barrels/lifting bags tied to the blocks at depth.

Inflatable's after block being sunk near the Tank.

The project was finally completed and filled with air in 1991. The tank is used quite a lot so the air does change quite well, but every so often the it is emptied, given a good clean out and refilled.

It is still quite strange to 'surface' and hold a conversation with your buddy with your depth gauge reading 12M!.

Follow the Tour... The Far Platform

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Pictures courtesy of Dave Parham.