RARE SAILING SHIP LOG GLASSES FOR CALCULATING THE SHIPS SPEED

RARE SAILING SHIP LOG GLASSES FOR CALCULATING THE SHIPS SPEED

£650 GBP

VERY GOOD 28 & 14 SECOND LOG GLASSES, ONE STAMED 28 SECONDS THE OTHER NUMBER 14 ( 14 SECONDS )

Dimensions

28"sec. 3.1/4"h.1.1/8"dia. 14"sec 3.1/2"h. 1"h.

Circa

1860

Country of manufacture

UK and Ireland

Categories: Navigational instruments, Sandglasses

Description

THE EARLY LOGS WERE USUALLY FOR 30 SECONDS ( CAPT. COOK ERA ) LATER IN THE 19TH C. UNIVERSAL USE OF THE 28 SECOND LOG GLASS CAME INTO BEING. THE LOG LINE WAS DIVIDED INTO EQUAL SEGMENTS OF 47ft 3″inches. THE SEGMENT WAS PROPORTIONATE TO A NAUTICAL MILE, SAME RATIO AS 28 SECOND IS TO AN HOUR ( 3600 SECONDS ) A NAUTICAL MILE BEING 6,070 FEET. THE SEGMENT OF 47.1/4 FEET MARKED BY KNOTS ON THE LOG LINE, THIS MEANS IF DURING A 28 SECOND RUN 142 FEET OF LINE ( 3 SEGS. ) WERE RUN OUT RELATING TO A SPEED OF 3 NAUTICAL MILES PER HOUR. A KNOT IS A NAUTICAL MILE. AS SAILING SHIPS BECAME FASTER ( TEA CLIPPERS AT 2O KNOTS OR MORE ) THE LOG LINES HAD BECOME MUCH LONGER E.G. 1000 feet TO MAKE THE SPEED CALCULATION SIMPLE THE TIME WAS CUT IN HALF ON THE SANDGLASS, SO THE FASTER SHIPS THEN USED A 14 SECOND LOG GLASS, THE SEGMENTS STAYED THE SAME LENGTH , USING THE SAME LOG LINE WITH A 14 SECOND GLASS, 8 KNOTS THEN BECAME 16 KNOTS PER HOUR OF SPEED THROUGH THE WATER.

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GB MikeRead

Mike Read Antique Sciences

Based in Lelant, near St Ives, Cornwall, I have been trading since 1979, buying and selling scientific instruments and nautical antiques. Over the years I have acquired many rare and wonderful items for the trade and collectors alike. I hope this continues. Mike Read. Email: michaelread060@gmail.com

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