CROSSING the Derwent at the moment provides a first-class view of a key piece of the machinery being brought to bear on the new Bridgewater Bridge.

Make that machineries, because there are a lot of them right there beside the old bridge.

At the centre is a blue and yellow cylinder, in reality a giant hydraulic hammer, designed to whack – as good a technical term as any – a series of steel piles into the river bottom.

But while it’s being whacked, that pile needs to be held still, in one position. That’s not easy when that blue sleeve that’s holding it is attached to a boat, that itself needs to be held still, in one position.

And all this is sitting on a river which is pushing about 90 cubic metres of water per second right underneath your keel.

So here’s how it’s done.

The boat is anchored in position by a series of ‘spuds’, the unglamorous steel posts surrounding the main action that’s mostly painted blue.

And the hammer itself, while locked on to the pile, is held upright so it always whacks the pile in the same way.

The job of holding the hammer aloft falls to a blue/black crawler crane with a 280 tonne lifting capacity. You can see the supporting chain at the top of the photo. The crane, at least, is sitting on massive steel structure that is the first section of the temporary bridge. Neither crane nor bridge section are going anywhere.

Driving the hammer, by the way, is a power pack, also blue, that’s attached to the hammer’s business end via a set of hefty black hoses.

What makes the process interesting (well, it’s difficult for those doing the work!) is the multiple elements involved – some fixed, some mobile and some moving rapidly.

Making it work, bringing all the pieces together, demands remarkable coordination.

The notion of ‘one position’ actually refers to a series of to-the-millimetre GPS coordinates the bridge surveyors determined early in the building process.

And it’s that precision over the position of the multiple elements and machineries is how the job gets done, no matter what the weather.

Or what the water is doing.