Have plane, might travel

A bout of severe weather exposes the vulnerability of fast-paced modern lifestyles

It is surprising how quickly you stop taking certain things for granted. Travelling, for instance.

At this moment I really shouldn’t be here. I am supposed to be 100 miles north of Fair Isle, in Unst, staying with my brother. But I’m not. I’m still at home.

After the gilded promises of last weekend, when the sun threatened to become a familiar visitor, we were brought firmly back to reality this week with some fairly horrific wind and rain, and, of course, transport has suffered. My flight on Friday afternoon was cancelled because of the weather, and a replacement flight on Saturday morning didn’t go either. It is now Sunday, but I will have to wait until tomorrow to travel. Well, hopefully tomorrow.

Travel delays here are common. Very common. The plane, which links Fair Isle and mainland Shetland, can’t fly if it is too windy, or the wind is in the wrong direction, or if it’s foggy, or if there’s low cloud, or snow, or ice, or if there are technical problems, which there are frustratingly often. (In fact, a brand new plane, just purchased by the council to provide the inter-island service, was recently stuck in Fair Isle for a week after suffering a cracked exhaust. The pilot and passengers had to be rescued by a second plane, and engineers were flown up from England to make the aircraft safe to remove.)

The ferry too is severely affected by the weather. During the winter months it sails only once a week: every Tuesday, in theory. But strong winds or heavy swell can make the crossing to Shetland impossible, and days, weeks even, can pass without a sailing.

The boat provides a vital link for the island, bringing essential food supplies, milk, bread and newspapers, so a delay can be a serious inconvenience. As of today, we have not had a boat for 11 days. However, relief has come from a special “freight plane”, which reached the island on Wednesday, carrying vegetables, milk, bread and other necessaries, so starvation is not on the cards just yet.

Shetland is a very windy place, with an average of 42 days of gales each year (a number that seems to be growing as the climate changes). Some of the strongest winds ever recorded in Britain have been recorded here, including an unofficial record gust of more than 150 knots, on New Year’s Day, 1992. Later that night, the anemometer which took the recording, at Muckle Flugga Lighthouse in Unst, blew away.

Last month, when mainland Britain was struck by strong winds, the Northern Isles were one of the few places to escape the gales. It was rather odd to see the chaos that erupted across the country. Here, winds of those speeds are not nearly so unusual, but the damage they cause tends to be minimal. Houses are built to withstand the weather, and significantly, there are no trees to blow over.

But with weather like that delays are something we get used to. When planning a journey off the island, it is prudent to allow several days extra travelling time just to be safe. And sometimes even that is not enough.

People spend so much time rushing around these days that even the slightest interruption to their schedule can throw them into fits of utter distress and helplessness. We rely on cars, trains, planes, buses and boats every day to get us where we want to be. Fast. But living in a place where our reliance is so easily undermined is a good reminder of how vulnerable that lifestyle really is.

Photographs: David Wheeler

Malachy Tallack is 26 and lives in Fair Isle. He is a singer-songwriter, journalist, and editor of the magazine Shetland Life.
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Inside Big Ben: why the world’s most famous clock will soon lose its bong

Every now and then, even the most famous of clocks need a bit of care.

London is soon going to lose one of its most familiar sounds when the world-famous Big Ben falls silent for repairs. The “bonging” chimes that have marked the passing of time for Londoners since 1859 will fall silent for months beginning in 2017 as part of a three-year £29m conservation project.

Of course, “Big Ben” is the nickname of the Great Bell and the bell itself is not in bad shape – even though it does have a huge crack in it.

The bell weighs nearly 14 tonnes and it cracked in 1859 when it was first bonged with a hammer that was way too heavy.

The crack was never repaired. Instead the bell was rotated one eighth of a turn and a lighter (200kg) hammer was installed. The cracked bell has a characteristic sound which we have all grown to love.

Big Ben strikes. UK Parliament.

Instead, it is the Elizabeth Tower (1859) and the clock mechanism (1854), designed by Denison and Airy, that need attention.

Any building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster.

Repairs to the tower are long overdue. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. There is water damage to the masonry and condensation problems will be addressed, too. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting.

Marvel of engineering

The clock mechanism itself is remarkable. In its 162-year history it has only had one major breakdown. In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. The resulting damage took months to repair.

The weights that drive the clock are, like the bells and hammers, unimaginably huge. The “drive train” that keeps the pendulum swinging and that turns the hands is driven by a weight of about 100kg. Two other weights that ring the bells are each over a tonne. If any of these weights falls out of control (as in the 1976 incident), they could do a lot of damage.

The pendulum suspension spring is especially critical because it holds up the huge pendulum bob which weighs 321kg. The swinging pendulum releases the “escapement” every two seconds which then turns the hands on the clock’s four faces. If you look very closely, you will see that the minute hand doesn’t move smoothly but it sits still most of the time, only moving on each tick by 1.5cm.

The pendulum swings back and forth 21,600 times a day. That’s nearly 8m times a year, bending the pendulum spring. Like any metal, it has the potential to suffer from fatigue. The pendulum needs to be lifted out of the clock so that the spring can be closely inspected.

The clock derives its remarkable accuracy in part from the temperature compensation which is built into the construction of the pendulum. This was yet another of John Harrison’s genius ideas (you probably know him from longitude fame). He came up with the solution of using metals of differing temperature expansion coefficient so that the pendulum doesn’t change in length as the temperature changes with the seasons.

In the Westminster clock, the pendulum shaft is made of concentric tubes of steel and zinc. A similar construction is described for the clock in Trinity College Cambridge and near perfect temperature compensation can be achieved. But zinc is a ductile metal and the tube deforms with time under the heavy load of the 321kg pendulum bob. This “creeping” will cause the temperature compensation to jam up and become less effective.

So stopping the clock will also be a good opportunity to dismantle the pendulum completely and to check that the zinc tube is sliding freely. This in itself is a few days' work.

What makes it tick

But the truly clever bit of this clock is the escapement. All clocks have one - it’s what makes the clock tick, quite literally. Denison developed his new gravity escapement especially for the Westminster clock. It decouples the driving force of the falling weight from the periodic force that maintains the motion of the pendulum. To this day, the best tower clocks in England use the gravity escapement leading to remarkable accuracy – better even than that of your quartz crystal wrist watch.

In Denison’s gravity escapement, the “tick” is the impact of the “legs” of the escapement colliding with hardened steel seats. Each collision causes microscopic damage which, accumulated over millions of collisions per year, causes wear and tear affecting the accuracy of the clock. It is impossible to inspect the escapement without stopping the clock. Part of the maintenance proposed during this stoppage is a thorough overhaul of the escapement and the other workings of the clock.

The Westminster clock is a remarkable icon for London and for England. For more than 150 years it has reminded us of each hour, tirelessly. That’s what I love about clocks – they seem to carry on without a fuss. But every now and then even the most famous of clocks need a bit of care. After this period of pampering, “Big Ben” ought to be set for another 100 or so years of trouble-free running.

The Conversation

Hugh Hunt is a Reader in Engineering Dynamics and Vibration at the University of Cambridge.

This article was originally published on The Conversation. Read the original article.