Never Mind the Bullocks, Here's the Science (26 page)

So it was not just the changing climate that booted the Norse out of Greenland.

There’s a lot to be said for local knowledge—and the joy of fishing.

Dragon Ships

A medieval prayer from the Middle Ages says: ‘From the fury of the Norsemen, good Lord deliver us.’

The Norsemen, or Vikings, had a terrible reputation. They got their money from exorbitant taxes, tributes, trade, outright extortion, daylight robbery and plain old piracy. At their peak, their power extended across all of Scotland, Ireland and England, through Europe, and deep into the Mediterranean Sea. And they did it all thanks to the Viking longship – the dreaded dragon ship.

These magnificent dragon ships could cross oceans, land on beaches and sail up rivers. They didn’t suddenly spring into existence – they were the peak of the evolution of 6,000 years of shipbuilding.

The evolution began with Scandinavian Stone Age dugout canoes, around 5,000 BC. The Stone Age boatwrights used flint tools to scrape out the inside of
soft, long-lasting linden trees. They were so skilful, even 7,000 years ago, that they could make a canoe with a wall only 2 cm thick. These canoes, which measured up to 10 m in length, were used for catching whales – and winning wars.

About 5,000 years ago, the boatwrights along the banks of the Åmose River in Denmark came up with a new trick. They made a row of holes along the upper edges of the sideboards of their canoes. Then they carved planks with matching holes, and tied them onto the side walls of their dugout. This increased the distance between the water and the top of the hull. These boats travelled safely to Norway and Sweden.

During the Bronze Age (from 2,000 BC to 500 BC), some of the features of the classic Viking ship appeared – such as the posts at each end, crowned with the heads of animals, snakes or dragons. This high post was actually the extension of protective timbers on the pointy end of the boat.

By the time of the Iron Age (500 BC-400 AD), the prow was a major feature of the boat. It took a lot of energy to make – but it was too tall and too weak to be used as a battering ram. However, it must have had some sort of protective or stabilising effect, because Iron Age shipbuilders put one at each end of the boat.

This was the world’s first real double-ended boat with wonderful engineering features.

The advantage of a double-ended warship was that it could reverse without having to turn. This could save the Norsemen’s lives when they had to suddenly retreat from a superior force.

It was also higher at the ends than in the middle. This stopped water from entering the boat.

The advantage of the deeper midsection was that it gave the boat a better grip on the water during a turn. In fact, by the end of the Viking era, the keel of the dragon ship was about 30 cm deeper in the centre section of the boat than at either end. A measurement of 30 cm is almost invisible in a boat 35 m long, but the Viking shipwrights incorporated this subtle curve, because it was needed.

There were a few different styles of longships.

The small levy ships had fewer than 20 rowing benches. The local communities had to keep some in good repair, to provide warriors for the king, whenever he sent around the symbolic war arrow.

The standard longships had up to 30 rowing benches.

Later in the Viking era the so-called great ships had more than 30 rowing benches. These great ships were 35 m long, about 3 m wide, and about 1 m high from the top plank to the keel. They weren’t called longships for nothing.

These dragon ships could cross an ocean, ride out a gale, cruise a river and land on any beach. They were both a troop carrier and a landing ship. They could discharge their crew of 60 armed warriors within a minute. They were definitely beautiful ships.

A song about the ship of King Harald Hardruler goes, ‘As Norsemen row the serpent, the riveted [ship] down the icy stream, it is like a sight of eagle’s wings’.

The dragon ships were constructed from the best materials. One recently excavated Viking longship had been made from 300-year-old trees. The planks were over 10 m long, without a single imperfection.

The Viking shipwrights would split the tree trunks in a radial pattern – like the spokes of a bicycle wheel radiating out from the centre. Splitting the timber gave
greater strength than sawing it. Using planks made from radially cut timbers from the same tree meant that they were all the same strength.

The ships were made from many overlapping planks. The advantage of having planks was that it was easy to make the curves that were needed. The disadvantage was that they could leak.

But the Vikings were hardy people. According to Norse law a ship was regarded as seaworthy if the crew didn’t have to bail it out more than three times in two days. Of course, the crew could decide to sail in the boat even if it was unseaworthy, but they weren’t forced to.

The Viking era ran only three centuries, from 800 to 1100 AD. During this time they travelled all around Scandinavia, deep into Russia, throughout the British Isles and into Europe as far south as Spain, and then on to the Mediterranean Sea as far east as the Black Sea.

Still, they could not effectively control the larger and richer states that they had overrun. They didn’t have the political experience, or the stable home society, or the wealth that was needed to build an empire. And the world itself had changed after 1100. Impregnable walls were built around city ports and navies were organised.

Soon the graceful dragon ships went the way of the beasts that they were named after. And so the magnificent fighting ships of the Vikings were replaced by prosaic cargo ships.

References

Arneborg, J., et al., ‘C-14 dating and the disappearance of Norsemen from Greenland’,
Europhysics News
, March 2003.

Diamond, Jared,
Collapse: How Societies Choose to Fail or Survive
, Camberwell, Victoria: Penguin, 2005, pp 179-276.

Four-wheel Drive Safety

A while ago, I was talking to a bunch of school kids after giving a fun/motivational science talk. At the time, my elder daughter was learning to drive, and so I asked them who was learning to drive, and in what type of vehicle. A few of them said they were learning in four-wheel drives (4WDs)—and they had been told that 4WDs were safer than standard passenger cars.

They were soooooo wrong. Four-wheel drive vehicles are not always safer, and in some cases are less safe.

The students and I ended up having a very long discussion, especially in light of the fact that 4WDs are popular family cars.

But first, what is a 4WD?

4WD, SUV, or What?

Back in the Old Days (before the arrival of the Range Rover in 1970), a 4WD was a fairly crude vehicle that fed power to both the front and rear axles. Assuming that there was a good road surface and no wheel spin, this gave you all four wheels driving the vehicle forward—hence the name four-wheel drive. It also sat higher than an average sedan. In the USA, the equivalent was a sports utility vehicle or SUV. Early 4WDs were utilitarian and were mainly used for agricultural purposes and in the military.

Why Get One?

One in five passenger vehicles sold in Australia is a 4WD. They are popular family cars, because they can carry lots of kids, have lots of boot space, and because many parents wrongly believe that these larger vehicles are inherently safer than smaller vehicles.

However, they do have another use. Australia has about one million kilometres of road, and about half of this is unsealed. If you venture out of the coastal areas that hold 80% of the population, you need a vehicle with a rugged suspension and body, and good ground clearance.

Then the luxury Range Rover arrived on the scene. It had a unique suspension, with long travel and high compliance on each wheel. In the earlier 4WDs the suspension was quite stiff, and each wheel moved up and down only a short distance when you went over rough ground. But in the Range Rover the suspension was quite floppy, and each wheel moved a larger distance up and down. This made it very comfortable to travel in. Surprisingly for the adherents of the old suspension, the Range Rover was also extremely capable in Outback conditions. (However, it had only a short range, thanks to its rather thirsty petrol engine.)

Even though the term 4WD (or SUV) included comfortable and luxury vehicles, they were all higher than the standard passenger car. They had, thanks to their greater ground clearance, the capability to travel in the Australian Outback.

But then the definition of a 4WD became complicated by the insertion of a four-wheel drive system into otherwise standard passenger cars. These vehicles rode at the same height as other
sedans, but the drive train now operated all four wheels. This was to give superior traction in slippery conditions.

But for this story, when I say 4WD, I mean the vehicles that definitely ride higher than the average sedan.

There are many arguments to consider in this complicated issue of car safety, so let’s run through them one at a time.

Increased Height

Thanks to improved technology, most 4WDs no longer feel like a truck to drive. In many cases, they drive almost like a regular car. This car-like feel lulls the inexperienced driver into a false sense of security.

Regardless of feeling a lot like a car, one problem with practically all 4WDs is that they have a higher centre of gravity.

This increased height comes from two factors. First, the wheels are usually bigger than those on a sedan, so the drive train sits a little higher. Second, the body is usually mounted higher above the drive train than in a sedan, to give extra ground clearance for rough territory.

In 2004, the US National Highway Traffic Safety Administration began putting vehicles through rollover tests. They found that 4WDs were far more likely to tip over than regular cars. And away from the laboratory, and in the specific example of rollovers associated with a road crash, SUVs are four times more likely to roll over than a conventional passenger car.

There’s not a lot the manufacturers can do to compensate for this higher centre of gravity, which makes it all too easy for a 4WD to tip over when a driver inadvertently takes the vehicle out of its stable equilibrium zone, e.g. swerving to avoid an animal.

Extra Weight

Another problem with 4WDs is that they are significantly heavier than regular cars.

The extra weight increases their braking distance. It also makes them far less nimble and less manoeuvrable in tricky situations. For a good example, think of a random pair of animals (of roughly the same size, but different weights) running fast then trying to change direction rapidly—say, a hippo and a horse. I’d have my money on the horse, for pulling the quick sidestep.

4WD Higher and Side Impacts

In a front collision, there is a lot of metal between you and the outside world. But in a side collision, there is only a door, some 10 cm thick, most of which is empty space. In 2002, 9,600 passengers in the USA died in side impact collisions.

Car doors are made from a few sheets of thin metal welded together. This means they are not very good at stopping a side impact from another car. So over the last few decades, car doors have been made stronger by having an anti-intrusion bar – a thick tube of very strong steel – welded in place just below the bottom of the window.

If you (in a sedan) get hit by another sedan from the side, the anti-intrusion bar will protect you. But if you are in a sedan, and get hit by a high-riding 4WD, its bumper bar will ride over the top of the anti-intrusion bar, come through the glass window and hit you in the upper body.

The problem is inherent in the 4WD being higher than a conventional sedan.

The Bigger the Better?

There are benefits to 4WD passengers associated with being in a heavier and higher vehicle.

But they are offset by the increased risk of rollovers, and the decreased manoeuvrability.

Big Fat Tyres

The big fat tyres on a 4WD are another safety problem.

When you turn the steering wheel, various metal gears, cogs and rods rotate and/or move in various directions, and after a bit of mucking around, force the metal front wheels to turn. But the metal wheel doesn’t touch the road. No, there’s a rubber tyre between the metal wheel and the road.