Little Buc: Ahoy, Followers! Ahoy, Giles!
Giles Hopkins: Good Morrow, Followers! Good Morrow, Little Buc!
Little Buc: I saw you on the Bridge Deck last night. You seemed captivated by the cadets measuring the angular distance between two visible objects.
Giles Hopkins: I certainly was! As I watched the cadets use their sextants to take readings, I was thinking that Master Jones and his crew missed out on using this navigational tool.
Little Buc: That’s right! The sextant was invented almost simultaneously by John Hadley in England and by Thomas Godfrey in Philadelphia, Pennsylvania in 1731. It wasn’t exactly like the modern sextant that the cadets use today, but it was quite similar.
Giles Hopkins: 1731? Master Jones missed that invention by 111 years!
Little Buc: How did Master Jones determine latitude without a sextant?
Giles Hopkins: Although the astrolabe had been in use for over a century, it was considered expensive and complicated to use. Historians aren’t sure whether Master Jones used an astrolabe or not. They do believe, however, that Master Jones used a cross-staff to shoot the sun and determine latitude.
Little Buc: When we visited Plimoth Plantation last summer, you showed me a reproduction of the cross-staff that was used when the Mayflower II made her voyage from England to Plymouth in 1957. It certainly was an interesting instrument! That cross-staff was larger than the sextants that the cadets use – and much bigger than me. The graduated staff was about three feet long. The sliding bar which was attached to the graduated staff at right angles was about twenty-six inches in length.
Here’s the photo that I snapped at Plimoth Plantation.
Giles Hopkins: To use the cross-staff, the navigator would align the horizon at the bottom of the vertical bar and the Sun at the top. If it was nighttime, he would use the North Star. This would allow him to measure the altitude of the Sun. As you can imagine, stormy weather and rough seas made using the cross-staff challenging, if not impossible.
Little Buc: I am a little confused. I wonder if there’s a video that will show our followers and me how a cross-staff worked.
Giles Hopkins: Here’s a video for you to watch, Giles. Later, I will post this video to show our followers how a cross-staff works.
Little Buc: Thanks, Giles! As I watched the video, I was imagining Master Jones on the Mayflower as he used his cross-staff.
Giles Hopkins: I have a question, Little Buc? Why do the cadets learn to use sextants? Surely they can determine location using the tools on the Bridge. Why go to all that trouble to find out where the TS Kennedy is located, when the Bridge already knows?
Little Buc: Many a cadet has asked that very question! The reason is simple. Even the best technology can fail. Although it is very unlikely, it could happen. If that ever happens, cadets trained at Massachusetts Maritime Academy could identify where they were just using their sextant and heavenly bodies.
Giles Hopkins: These cadets will always be well-prepared, wherever they are in the world.
Little Buc: I’m curious, how did Captain Jones identify the depth of the ocean around him? I am pretty sure that Mayflower was not equipped with the Echo Sounder that the TS Kennedy relies on. Captain Campbell and his crew use the Echo Sounder to measure the depth of the water below the ship’s bottom using sound waves. The Echo Sounder transmits sound waves and an audio pulse. This bounces off the ocean floor, returning as an echo to the source.
Giles Hopkins: Master Jones had two different type of lead lines. One was called the “dipsie line” or the deep sea line. This was used to determine if land was nearby by checking if the seafloor was changing. The dipsie line was a lead weight attached to a nine-hundred foot piece of line. Sticky fat was added to the bottom of the weight before it was dropped. The fat would pick up sand that it came in contact with. When the ocean floor changed from mud or rock to sand, that meant land was near. When Mayflower was in shallow water, Master Jones and his crew would use a sounding line to calculate specific depth readings. The lead line was quite simple – just a rope with heavy piece of lead tied to one end.
Little Buc: That’s it? Just a weight attached to a rope? What did that help Master Jones know how deep the water was around Mayflower?
Giles Hopkins: The line was marked in fathoms.
Little Buc: I’ve heard Marine Transportation majors talking about fathoms. One fathom is equal to six feet. How did the lead line work?
Giles Hopkins: The lead line was marked off to show two, three, five, seven, and fifteen fathoms. One of the crew members would throw the lead line overboard. He would watch the markings on the line as it sank down into the water and hit the bottom.
Later, I will share a video that demonstrates how the lead line works.
Little Buc: I am sure that Captain Campbell and the crew are happy to be using an Echo Sounder instead of a lead line.
Giles Hopkins: Master Jones would be amazed at all of this progress! Let’s head up to the Bridge and tell the cadets on watch about lead lines and cross-staffs!
Little Buc: Good idea! Wishing you a great day, Followers!