Effin mensuration

Statue of Dr Johnson near his birthplace in Lichfield

The learned readers of this site will not need to be reminded of the sapient advice of the late Dr Samuel Johnson:

[…] no man should travel unprovided with instruments for taking heights and distances.

There is yet another cause of errour not always easily surmounted, though more dangerous to the veracity of itinerary narratives, than imperfect mensuration. An observer deeply impressed by any remarkable spectacle, does not suppose, that the traces will soon vanish from his mind, and having commonly no great convenience for writing, defers the description to a time of more leisure, and better accommodation. […]

To this dilatory notation must be imputed the false relations of travellers, where there is no imaginable motive to deceive.

Samuel Johnson A Journey to the Western Islands of Scotland W Strahan and T Cadell 1775

The good doctor would, I think, have welcomed the invention of the digital camera with inbuild chronometer. Equipped with just such a device I arrived yesterday at the first lock on the Royal Canal to witness the lifting of the railway bridge and the passage thereunder of fleets of boats. I thought it would be interesting to record how long each stage took.

I have written before about this bridge: reporting a question by Maureen O’Sullivan TD in October 2013 and another in November 2013 and providing statistics on usage a few days later:

• only 58 boats went through in 2013
• the bridge was lifted on seven dates
• two other scheduled lifts were cancelled as no boats wanted to travel
• Irish Rail charged Waterways Ireland €1200 per weekday lift and €2000 per weekend lift.

The first 45 minutes

A lift scheduled for early July 2014 was cancelled; yesterday’s lift catered for just two boats, whose passage was assisted or monitored by eight Irish Rail staff and four from Waterways Ireland. Four of the Irish Rail people may have been in training as others seemed to be demonstrating things to them, but that’s only a guess. Three of the WI staff travelled together in WI’s stealth van and operated the first lock; the other, who travelled separately in a 4WD vehicle, visited from time to time. As far as I could see there was no contact between the Irish Rail and WI teams.

The bridge was scheduled to be lifted by 1100.

Before the lift: 0945. The lifting bridge is on the right of the photo

One minute later: 0946. A separate group of workers, perhaps contractors, is going down the west side of Spencer Dock with equipment

Four men still on the bridge 0949

Two minutes later

On the bridge 0956

Still there 0958

One minute later

The bridge 1006

The bridge 1012

The bridge 1015: another person approaches

Six men at the bridge at 1020

A seventh man approaches at 1028

Preparing to lift

The preparation stage, presumably involving the unlocking of some mechanism, took about five minutes altogether.

One man worked on the far end while another walked to do the same at the near end

An eighth man, behind the fence on the right, seemed to summon two of the men on the bridge

They went to this building, which I guess houses the controls for the bridge

Meanwhile work continued on the bridge itself

Almost done

A final check

Everybody was off the bridge by 1033

Lifting

The lift itself took just over nine minutes; the bridge was up before 1044, in good time for the arrival of the boats.

After about one minute

Another minute later

Another minute (or so)

About four minutes have elapsed

After five minutes. The sides are clear of the water in which they usually rest; they are dripping on to the canal below

Six minutes in

Seven minutes

The men behind the fence may be controlling the lift

Not much further to go

Eight minutes

It’s up

One of the jacks

Side view (taken after the boats had gone through)

Water under the bridge

Boats go through

It took just over three minutes for the two boats to go under the bridge.

Cruiser approaches; steel boat visible through the bridge

Cruiser about to enter

Heads down

Half way through

Leaving

Out

Steel boat entering

Almost through

Looking ahead to the lock

Done

I did not record the lowering of the bridge, which I presume took much the same time as the raising.

Preparation 5 minutes, lifting 9 minutes, passage 3 minutes, lowering and locking say another 14 minutes: say 45 minutes altogether, allowing some margin. But a large number of boats would take much longer as the rate at which they could move on from the bridge would be limited by the time taken to work through the lock.