wood ships , iron men

[GrowleyMonster]

Originally Posted by CaptainGrey

Lunars. They knew how to get the time through lunar observation. That's probably how Slocum managed to navigate with a $2 tin clock.

Sort of. He checked his clock/longitude by lunar distance, and found it to not be so far off, and if I recall correctly, he didn't bother with Lunars again after that.



It was a tedious bit of math and not for the uneducated. So while it could be used, it was not generally used. Particularly before solution tables were available.

[GrowleyMonster]

Originally Posted by kleenbreeze

To calculate longitude with a clock you need an accurate clock set to grenich mean time and then you take a reading at noon each day to determine the difference, each hour = 15 degrees. And that noon is not the noon on your ipad, it is the sun directly overhead. Difficult to measure accurately, esp on a moving vessel, but I think they used the masts as sights to determine when the sun was directly overhead.

No. At some time before LAN, a sight was taken. And another and another, continually. The height of the Sun would be observed to increase, hang, and then begin to decrease. The highest observation was then used for finding Latitude. The sun could only be directly overhead when Latitude and Declination coincide, a rare coincidence. The Sun would normally pass to the North or to the South depending on the ship's Latitude and Declination of the Sun.

[Velella99]

Originally Posted by GrowleyMonster

No. At some time before LAN, a sight was taken. And another and another, continually. The height of the Sun would be observed to increase, hang, and then begin to decrease. The highest observation was then used for finding Latitude. The sun could only be directly overhead when Latitude and Declination coincide, a rare coincidence. The Sun would normally pass to the North or to the South depending on the ship's Latitude and Declination of the Sun.

There are many books about this era of maritime history but the one that fascinates me is the story of the Batavia (1629) which was the flagship of the Dutch East India company. Like all such merchant ships and voyages from Holland to the Dutch East Indies (now Indonesia), they came under the Cape of Good Hope and had to determine their position relative to Australia and turn left in time - or hit it. The coast of Western Australia is littered with Dutch ships that "didn't turn left in time". They had various methods to try to determine a boat speed including throwing a chip overboard and counting the heartbeats. Sure, they blew it a few times; but considering the level of seamanship these people attained, it's gob smacking where they could take their ships considering any wind abaft of abeam had to be waited for and further, any such wind had to be waited for in strength.