Roy Hart doesn't so much like messing about on the river - more like messing about with the river.

He lives at Battlesbridge, just above the lock for which he has just designed and constructed a new set of £25,000 gates.

Roy, 62, the founder of ski supplies shop Skeetex, decidedly to throw a party to launch the latest addition to his watery home.

Battlesbridge may be one of the most historic sites in Essex, but it is set to become a role-model for 21st century living.

"I want to bring it into the post-nuclear age," says Roy.

First, though, came the party. "I just invited a few local people, old friends and people who love the river like I do," said Roy. The guests included six boats containing Roy's sailing friends and rivals.

They arrived by river rather than car, mooring alongside the Battlesbridge antiques centre.

When it comes to a sense of style, no stretch limo could possibly match such an entrance, and there were practical advantages as well.

As one guest pointed out: "You don't need to call a taxi when you want to go home."

At high tide, around 12.45pm, party-goers trooped to the lock gates. The national flag was raised. A can of beer was poured over the top of the beams, and then some more, to avoid any danger of the gates drying out.

Then the gates were declared open, even though, at this stage, they were distinctly closed. On the bank lay the withered remnants of the old, worn-out gates.

"They did a good job for 20 years," said Roy, "but we realised last year they were wearing out."

Lock gate-making isn't normally a job for enthusiastic amateurs, but then nor is diverting the course of rivers.

The new gates - weighing 19 tonnes - were constructed using pine beams and metal sluices. The basic work was completed by two Harts, Roy and his son Justin. Woodham Ferrers engineers the Keeble brothers, assisted with some of the more specialised milling.

But the design and draughtsmanship for the working drawings was entirely the work of Roy.

"Ten minutes on the back of a scrap of paper," he says.

The lock gates were moved into place on makeshift rollers, then craned into position to sit on the original pins.

While all this was taking place, the Crouch, a river hovering meekly in the background, proved a bit of a disappointment for those who like to be awed by the blind forces of nature.

The wuss of a waterway meekly did as it was told by Roy of the River, consenting to being diverted through an alternative channel while work was completed on the gates.

The new ones are a picturesque addition to the riverside scene at Battlesbridge, but they are not there just to be idyllic.

Their role is to harness the tide. The gates will build up a head of water that will power a generator.

"Once all that is built, I am going to buy myself a little electric car, a Gee Whiz," Roy said.

"It will be hooked up to the generator, a car powered by the river."

The river will also provide power for the new seafood restaurant planned for the old Battlesbridge sail-loft and modelled on the famous shed in Mersea.

First, though, he has another adventure in mind. Having put the tides of the Crouch in their place, Roy is seeking bigger game - nothing less than Europe's greatest tidal river.

"I want to sail all the way down the Severn from top to bottom," he said.

He adds: "The only problem is that to get all the things done I want to do, I need to live forever."

Roy Hart is working on that one, too.