Posted by: Rob Viens | April 30, 2013

Gales, Foul Winds and Fair Breezes

For the next several days, as the Beagle sailed north, Darwin found himself obsessed with the wind.  To be fair, on a sailing ship, life was all about the wind – you would be doomed if the breeze turned foul. But it is interesting how it seems to dominate the next few days of his journal:

“It blew half a gale of wind; but it was fair & we scudded before it. — Our decks fully deserved their nickname of a “half tide rock”; so constantly did the water flow over them.” (April 20)

“At noon 300 miles from Maldonado, with a foul wind.” (April 21)

“Our usual alternation of a gale of wind & a fine day.” (April 22/23)

And Wednesday brought more than just wind:

“We are off the mouth of the Plata. At night there was a great deal of lightning; if a hurricane had been coming, the sky could not have looked much more angry. — Probably we shall hear there has been at M. Video a tremendous Pampero. Our Royal mast head shone with St Elmos fire & therefore according to all good sailors no ill luck followed. — It is curious how the R. Plata seems to form a nucleus for thunder storms; phenomena which both to the South & North of it are comparatively rare.” (April 24) (See A Mighty Pampero and Watching a 19th Century “Plasma Screen” for more on these meteorological phenomenon.)

“At daybreak we found a current had set us several miles to leeward of Maldonado; as the breeze was both strong & fair the Captain determined to run on to M: Video.” (April 25/26)

ALl this talk of breezes led me to thinking I’d write a few words about the wind today. So here goes…

As you may recall, Captain FitzRoy was somewhat obsessed with the weather himself – trying to learn how to use air pressure to predict storms at sea and save lives. FitzRoy’s teacher and supporter, Francis Beaufort, was even more interested in the wind and, in fact, is probably best know for the Wind Force Scale that now bears his name. Furthermore, although the scale goes back to the early 1800’s, it was FitzRoy who was actually one of the first sea captains to really test out the scale during his Beagle voyage. (It was adopted and used by all ships in the Royal Navy in 1838, shortly after FitzRoy’s “trial run”).

Sir Francis Beaufort was born in Ireland in the late 1700’s and one story suggests that his life was shaped by a shipwreck he experienced as a young man – a wreck that was supposedly caused by a bad nautical chart.  For the rest of his life, Beaufort was involved in coastal surveying, creating accurate nautical charts, and better understanding the weather – all in the name of making the sea a safer place for sailors and their ships.

Sir Francis Beaufort by Stephen Pearce

Sir Francis Beaufort

In the 1790’s Beaufort joined the Royal Navy and quickly rose through the ranks, achieving the rank of commander in 1800 and captain in 1811. During this time he served in for the navy in the Napoleonic Wars (where we received several injuries) and was tasked with survey work – even surveying the mouth of the Rio de la Plata (where Darwin had arrived on April 24, 1833).

A couple of years before the Beagle started its second voyage (in 1829), Francis Beaufort became the British Admiralty Hydrographer of the Navy – a post he would hold for 25 years. During that time he promoted science as a member of the Royal Society and helped to found the Royal Geographic Society. He achieved the rank of Rear Admiral in 1846 and was knighted 2 years later.

But Beaufort’s most memorable accomplishment was probably the creation of a standardized wind force scale – a scale that bears his name today.  Up until this point, there was no quantifiable meaning of a gale or breeze – so their usage was inconsistent.  Beaufort, building on the work of earlier attempts, standardized the terms by creating a scale that ranged from 0 to 12 – thereby allowing those who observed the weather to “speak the same language”. Initially the scale was based on the way the wind impacted a ship and its sails, though over the years it became more directly related to wind sped and oceanic conditions.  Here is what the version that Beaufort gave to Robert FitzRoy in 1831 looked like  (from the Weather Doctor):

Beaufort Wind Force Scale

Since it was adopted by the Royal Navy in 1838, the scale has been modified and standardized to specific wind speeds, ocean conditions and wave heights.  But the basic principle (and the ranking from 0-12) still remains the same. Here is a modern version of the scale (fancy version – such as the one shown here – also include pictures of the oceanic conditions):

Beaufort Wind Force Scale

If you want to get a sense of what these wind speeds translate to in the real world, check out this short video showing a man in a wind tunnel exposed to winds ranging up to about a 7 on the Beaufort Scale. Now picture what this must feel like on a small sailing vessel. Keep in mind that winds would have get to be about 2x faster than the highest speeds in the video to reach the minimum of a 12 on the scale.

 

By the way – it appears that Darwin was not using Beaufort’s scale in his diary entries, as the names he uses (e.g., foul gale, gale of wind, etc.) do not match the names on the official scales shown above.  I find this interesting because (1) FitzRoy seemed to share a lot of his meteorological ideas with Darwin and (2) Darwin loved to describe things accurately – in many cases uses calibrated scales such as Werner’s color scales mentioned in earlier posts (see A Thousand Shades of Blue). It seems like he should have known about the scale by now. (RJV)

 

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Responses

  1. Now I finally understand better Beaufort scale 😉


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