Let’s finish our exploration of the “Treasures from the Girona” permanent exhibit, Ulster Museum, Belfast, Northern Ireland.
One hundred and eighty five (185) years after La Girona ran aground and broke up on the, later named, Spanish Rocks, the first reliable navigational chronometer was tested (1773). The navigators of the Spanish Armada remnants were sore pressed to follow the orders of their commander (see below) because (1) Spanish charts were incomplete and inaccurate (2) without accurate time keeping they were only able to reliably measure the location north/south (latitude), not east/west (longitude). Without this, navigators used Dead Reckoning, they measured current position from the last position, heading (direction of motion), and speed.
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The astrolab (below), used to measure the angle between a heavenly body (sun/moon/star) and the horizon at a given time of day, obtained the latitude. The dividers used on the (unreliable) charts. A weight on a measured cord determined the depth of the bottom. Not recovered was the instrument for estimating speed. It is a length of rope knotted at set intervals and attached to a “chip log” resistant to passage through water. Thrown into the water a sailor counted how many knots passed by in a given time, thus the designation, still used today, of speed in “knots”.
Sound (a whistle) was the method used for command and control by both Spanish and British.
Interesting odds and ends.
Evidence of trade between England and Spain.