Daily Archives: May 9, 2020

Maybe that’s why 18

A reader—who goes by the nomme de keyboard ‘Good Luck’—was intrigued by my question: Why did Magellan take 18 sandglasses on his voyage of circumnavigation? The result was Good Luck found these fascinating articles about Magellan’s voyage and the instruments of navigation/timekeeping available to him. What follows below are his comments and links:

Check out the site below. It indicates there were sandglasses of different time periods and multiple sandglasses might be used to improve accuracy. It also seems possible there were extras in case of breakage.


The article at the link below discusses the use of 14-second and 28-second sandglasses to determine speed. It also describes the use of a 30 minute sandglass used in conjunction with a transverse board to record course and speed. Combined with the 30 minute and 4 hour sandglasses used to measure shifts and watches, as discussed in my previous post, it appears a ship could have had sandglasses of various timespans running at the same time.


The link below provides some information on the inventory Magellan had, part of which is quoted below.

“The fleet that set out employed the best ships and navigation devices of the time: 23 navigation charts, 35 compasses, six pairs of compasses, 21 quadrants, seven astrolabes and 18 sandglasses, among other instruments.”


I can not tell if the inventory listed above was per ship or if it was spread across the five ships that started the voyage. In either case, there appears to be significant redundancy in the compasses, quadrants, and astrolabes, so it seems possible a portion of the 18 sandglasses may have been redundant as well.

So, considering multiple uses, multiple timeframes, likely redundancy, and possibly supporting five ships, having multiple sandglasses makes sense. As to why exactly 18 . . . ?

Thank you, Good Luck! If you change your mind about a drawing just give me a shout.

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