The Captain Nemo of Bow: Gerald Harris spends his Sundays cruising the canals of east London in his home-made sub. Mark Handscomb climbs aboard

STRANGE things happen in canals, especially in east London. While staring idly at the water last weekend, I was surprised to see what looked like a miniature U-boat rise to the surface of a canal lock in Hackney. A group of anglers fishing from the towpath were terrified. I regretted drinking too much the night before.

The handles on the hatch turned and out popped Gerald Harris, like a rabbit from a magician's top hat. He gave a friendly wave and puttered over for a chat by the canal bank.

Bored with mending cars and obsessed by submarines, Mr Harris decided to make his own submersible out of old oil drums. 'When I first started welding the oil drums together, people thought I had gone barmy,' he says. 'But usually that's a great spur to me. After all, it's not like launching a space rocket, it's quite a simple thing.'

The oil drums make up the boat's hull and conning tower. A battered Ford Cortina provided parts for the steering mechanism and wiring. Mr Harris's friendship with an elderly gentleman at the local television repair shop led to a steady supply of electrical parts that had lain abandoned for years. Other people donated useful bits of scrap and a several local engineering firms forgot the recession and offered him ball bearings for free.

Known as 'The Captain Nemo of Bow' in his local pub, Mr Harris now enjoys celebrity status. He has given up his job as a car mechanic and spent the past six months hunched over a lathe in a friend's garage, paring away the parts for the submarine. 'The most difficult thing was getting her to sink,' he says.

'There are tiny leaks here and there,' he admits, 'but after a couple of hours, there'll only be a couple of pints of water inside. I've fitted a bilge pump now so you don't get a wet bum.'

Christened the Saucy Sue, his sub dives and sails in much the same way as a naval submarine, but there are several important differences. Instead of sophisticated satellite technology, the communications system on Mr Harris's submarine is dependent on a rubber duck. 'I carry a portable telephone on board, just in case of emergencies,' he says. 'To make it work underwater, I had to fit an extension aerial to the surface, which is kept afloat by a rubber duck, so it's quite easy to spot on the water.'

Car batteries provide the power and there is no periscope, although Mr Harris says he will continue to experiment with his wife's make-up mirrors until he develops something satisfactory.

The Saucy Sue owes her origins to Mr Harris's games with squeezy bottles in his bath. 'I would experiment with Plasticine and elastic bands to figure out where to put the weight,' he says. This developed into a wooden mock-up, built in his cellar. By the time it was finished, it looked so convincing that the gas man mistook it for a real submarine. 'He asked me how I was going to get it out. I said I was going to flood the cellar,' Mr Harris says. 'He just read the meter and cleared off.'

Fitting inside an oil drum submarine is not easy. You need hinges in your knees to manoeuvre past all the copper pipes. A Perspex window at the front enables you to see where you are going, and the controls to make her dive and, hopefully, rise are as complex as plumbing in your own washing machine.

As I bobbed about on the waves, I could not help thinking about Second World War films and all those sailors who met a watery grave as their submarines became steel coffins as a result of enemy action. When the manhole cover clunks shut, you realise why sailing in a one-man submarine is not for those who suffer from claustrophobia. Mr Harris insists his submarine is safe. However, he did have a problem with carbon dioxide gas leaking into the hull and poisoning his air supply. 'I became all panicky and said to myself: 'That's not like me.' But I just turned on my oxygen supply, put my nose clip on, surfaced and here I am to tell the tale.

'Scuba diving never really fulfilled me,' he adds. 'If you go diving in a wet suit, you're freezing cold, wet and miserable, whereas in this, you can relax, potter about and light a cigarette. The only trouble is that you end up smoking the same cigarette three or four times because I haven't got round to fitting any air circulation in there.'

Now that the Saucy Sue has successfully completed her trials, Mr Harris dreams of perfect Sunday afternoons spent sailing through the canal to meet friends for a quiet drink at a pub by the towpath. He is keen to build a craft to take a couple of friends along for a deep sea adventure. Exploring wrecks submerged in Scapa Flow and plans to sail the Irish Sea are next on his list.

'It's the ultimate in getting away from everything,' he says. 'Once you are a couple of feet under the surface, you can sit quietly on the bottom and no one will know you are there.

'Sometimes it's a bit dark and gloomy down there. The bottom of the canal is dirty, but the water itself is quite a nice green colour.'

Mr Harris plans to build a larger, passenger-carrying version and is looking for sponsorship to develop his ideas. He has formed the Society for Underwater Boats and can supply plans for those who would like to build their own miniature submarine on a budget.

'I've had a few sleepless nights and nightmares about drowning. Will it work? Should I be doing this? But you've got to have faith in what you make. Usually what I make works. If I fix something, it's fixed for good.'

(Photograph omitted)