Welcome to Log Lines, the blog of the USS Constitution Museum’s archives and collections!
Why did we call this blog “Log Lines?” In the early nineteenth century, mariners determined the speed of ships using an instrument called a “chip log” or “log line.” The chip was a triangular slip of wood weighted along its bottom edge with a bit of lead. A long, thin rope called a “log line” connected the chip to a hand-held reel. This rope was marked with knots every 47 feet 3 inches. When sailor wished to determine the speed of the vessel (on Constitution this was performed every hour when at sea), he heaved the chip over the stern, held the reel clear of the rail, and let the log line run out as the ship moved through the water. After 28 seconds, the man with the reel stopped the line. As he pulled the chip back in, he noted how many knots (and fractions after the last knot) had run out and made a notation on a slate. The ship’s speed, recorded as “knots per hour,” was in turn entered in the ship’s log book and used by the sailing master to determine the ship’s course run and ultimately her location on the wide expanse of sea.
This blog will be a navigation tool of sorts. We hope our readers will gain a deeper insight into the long and fascinating history of America’s favorite ship. She hasn’t sailed along at 13 knots (her fastest recorded speed) in very long time, but our knowledge of the ship and those who sailed her has moved ahead at a surprising clip over the past few decades. Stay tuned as we capture new stories and bring them back to port!
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| Chip log, line, and reel A New Universal Dictionary of the Marine William Burney, 1815 |
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| 28-second glass from A New Universal Dictionary of the Marine William Burney, 1815 |
Dear Jack .. is this really true? Was the entry in the ships log book really "knots per hour"?? .. per hour?? Why would they reffer to an hour, if the measurment was done within 28 seconds? .. todays definition is 1 kn equals 1 seamile PER HOUR. I believe they just wrote xy knots – and every seaman knew.. besides this note: thanks for showing and for the explanation
Perhaps it would be better to say "knots each hour." Most logbooks of the period included four columns on the left size, lettered H, K, F, and Course. The first recorded the hours of the day (24, of course). The second and third recorded the knots and fathoms run out when the log was cast during a particular hour. The fourth recorded the course steered. A typical entry might simply read 5|7|4|E (that is, at 5 o'clock the ship was making 7 knots 4 fathoms and was steering to the eastward) Thanks for your comments!