NavList:

Brad,

The 10th century Indian Ocean navigators set the terminal point of their Kamal when at port. This enabled them to get back to that point by first sailing north or south until at the designated Kamal reading then east or west until landfall. The Kamal was just a rectangular piece of wood with a string through the middle. The navigator would knot the string so that when held by the teeth the wood rectangle would have the horizon along the bottom and Polaris tangent to the top. Every port of call had a designated knot on the string.

You say:
" wait for the altitude of a body, say the sun, to be a specific angle at a specific time. Correct? Similar to the Time Sight determination of longitude. When the sun is above 5 degrees, I measure its altitude and compute longitude because I know my latitude."

No time sights done here. Azimuth and intercepts are used exclusively. When the island is the assumed position the navigator knows instantly how far to fly to get to the LOP where a 90* course change will be made to run down the LOP ( no plotting just an ETA to the 90* course change ). Then when on the line observations are continued so there is instant feed back as to whether left or right of the LOP track line which passes through the island. Time of arrival to the island then becomes an unknown. The offset is needed so that the navigator will be sure of which way to change course 90*.

Greg Rudzinski

Re: Sun lines was Moonrise video
From: Brad Morris
Date: 2013 May 3, 19:15 -0400
I've got a few basic questions about this too.

1) I get how you could stay on a latitude line by measuring the altitude of Polaris. Polaris too low? Turn northward. Polaris too high? Turn southward. That keeps me on a specific latitude.

Now the terminal point is interesting. How do I know it?

I wait for the altitude of a body, say the sun, to be a specific angle at a specific time. Correct? Similar to the Time Sight determination of longitude. When the sun is above 5 degrees, I measure its altitude and compute longitude because I know my latitude.

Assume I'm heading due east. If the time arrives and the body is too low, I think I've had a headwind and therefore, continue to head eastward. Conversely, if the time arrives and the sun's angle is too high, then I've had a tailwind and have gone too far.

I think, therefore, that I monitor the angle while checking the time. Since there are a large number of combinations of angle and time that equal the desired destination, it may be difficult to precompute all of these apriori. How then is this determined? Graphical? Tabular? Just keep solving for longitude based on altitude? I recognize that with enough computing power, this isn't an issue, but that hardly represents the solution until the electronic calculator.

2) Howland Island is fairly close to the equator, so its unlikely they used Polaris. I assume that other stars were used to stay on the course and way points by time. Further, if the trip is not truly east/west, then the altitude/time combination for each selected waypoint/star is just the celestial solution. Works the same way, just not on a line of latitude.

I think I understand how it it works when the air is still and the course made good matches the expected. Its when there are large head or tail winds that cause the combinatorial explosion of pairs. A combinatorial explosion that precludes pre-computation. How is this adjustment accounted for?

Brad

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