NavList:

Over the Spring break, I had the opportunity to tour "Ships of the Sea Maritime Museum" in Savannah, GA.  A lovely collection of ships from the Civil War era, to commercial freighters and liners to naval ships christened ‘Savannah’.

The navigation instruments collection was surprisingly good with back staffs, cross staff, several sextants, compasses, early charts and more.

Within the collection were two wood rulers, one engraved "Navigation Scale Improved by B Donn". One scale is labeled Secants. These are the first I have seen that specifically call out navigation.

The display title reads:

4. Gunther Rules
English, early 19th century
The forerunner of the slide rule, named after the 17th-century English mathematician Edumand Gunther, this device was used by sailors for two hundred years to make quick mathematical calculations at sea.


There are numerous internet sites with reference to Gunther Rules for general calculation but none mention designs specific for navigation as this pair claim. Attached is a set of images detailing all parts of the 'Navigaiton' rules. Perhaps NavList members have some insights into what these scales are and how they facilitate navigation differently than regular Gunther Rules would have.

 

Ed Popko

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