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Timid Virgins Make Dull Companions

February 18, 2016

Daystar's compass
by Nicole
At anchor, French Lagoon, St. Martin

 Have you ever heard the phrase Timid Virgins Make Dull Companions? It is a mnemonic that helps you steer and navigate your boat. If you want to sail somewhere, you don't just point your boat and go.  It is a lot more complicated. You have to take into account many variables such as wind and current. Tools like the compass help. The compass may seem simple, but even that is not as easy as people think.

Compasses were invented by the Chinese as early as 1000 BC, and were used all over the world. They used an iron needle suspended over lodestone, which is iron oxide. The iron needle always points north, because of the magnetic pull of the Earth. In Europe, however, one had to be careful. The strange device that always pointed in the same direction was thought to be witchcraft.

Compasses have 32 markings on them called points. In the olden days, sailors were expected to be able to, "box the compass,' and name off every point rapidly and in order.

An example of the difference between true and magnetic north

One's compass is vital to helping one steer the boat. It would be almost impossible without it. North on the compass, however, is usually not the direction to the north pole, or true north. The north on one's compass points to magnetic north, which is different than true north. The difference between these is called variation. In other words, you could be sailing magnetic north and actually be sailing NNE (north northeast). This would be an easy thing to overcome if variation didn't change, but variation changes from year to year and from place to place. Between 1580 and 1850, the variation in London changed over 34 degrees. Variation changes because the magnetic north pole moves. It averages a speed of 10 to 15 miles per year, but it moves daily as well. It moves in an elliptical shape around its average position. The elliptical path gets bigger when there are solar flares on the sun. There is a place off the coast of Australia where, in the length of two football fields, The variation changes more than
90 degrees. If you don't know the variation, then you don't actually know which way you are steering.

A variation map, showing the different levels of variation around the world

Binnacle with spheres to counteract deviation.

Another thing to take into account when steering is deviation. Your compass might not even point to magnetic north, either. It might be a few degrees off. This is called deviation, and it would make it even harder to steer the boat accurately. Every compass has its own idiosyncrasies, which causes its deviation. An even bigger source of deviation on steel ships is the metal of the hull. To fix this, they would put soft iron and other magnets around the compass to counteract the ship, and even today steel ships have them. To make things even more complicated, deviation also can change depending on the direction of the ship and how much the ship is heeled. Amazingly, if a steel ship is on one course for too long, the deviation may change.

The black line shows the movement of magnetic north in the past 400 years

Another extraordinary thing is that the poles eventually will change positions. The earth’s magnetic field has decreased by five percent in the past century. In a couple hundred to a few thousand years the magnetic field will cease to exist. Birds won’t be able to navigate, compasses won’t work, ships wouldn’t be able to navigate. Eventually, after a long stretch of a non-magnetic earth, the magnetic field will return. It will get stronger, but with one difference: this time, the compasses will point south.

Compasses and our magnetic earth are fascinating, and they are vital to being able to steer the boat. The mnemonic Timid Virgins Make Dull Companions helps with this:

Start with Timid, or True, the true direction from your boat to your destination.
Add to that Virgins, or Variation, the difference between true and magnetic.
That results in Make, or Magnetic, the direction that your compass shows.
Add to that Dull, or Deviation, how far off from magnetic north your compass actually is.
This give you Companions, or Compass, the reading you should actually point on your compass.

So to figure out which direction you should go according to your compass, you will use this:

Timid/True plus Virgins/Variation equals Make/Magnetic. Add that to Dull/Deviation, and you get what you should steer on the Companions/Compass.

Wil Davis said...

Conversely, going from Compass to True the mnemonic is Can Dead Men Vote Twice At Elections. Compass, Deviation, Magnetic, Variation, True, Add East.