NavList:

I am glad to see that Kermit and Peter agree with the latitude calculated.  This, being real-world data, is prone to errors of sight taking.  The LAN observation was a single sight of a 10 part sight for position around noon.  Sadly, while this was my highest Hs, it was also in error, being 1.1 minutes above what it should have been and "fooled" me into thinking it was LAN, when it fact it was 2 minutes early.  So while the calculations may be perfect, the result will not be.  The actual position at 13:20 local was 6 degrees 56.0' South and 71 degrees 39.2' East as the ship traveled on a course of 120 degrees true at 13.4 knots.  My calculated position from the full 10 LOP's was 6 deg 56.0' South and longitude 71 deg 42.3' East.  So while the 10 lines gave me a perfect latitude, the longitude was 3.1' off.

 

Given that the captain insisted we stay within television range, we were following a short 3 legged track line, so the real position did not change but a few miles in those 4 hours.

 

At the Lunar time, which was 1616-43 LT, I was having a bit of trouble with clouds.  The first set of sun/moon altitudes were at 1612 and 1613 respectively, and the second set were 1617 and 1618.  The GPS position was 7 deg 03.6' S and 72 deg 7.0' East.  This was certainly better than most of my sun-moon lunars which seem to be far less accurate for me than other lunars.

 

Jeremy

 

1)  Lat ~ S 6 deg 55.6'

2)  UTC ~ 10:18:07

Peter Hakel

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From: "Anabasis75@aol.com" <Anabasis75@aol.com>
To: NavList@fer3.com
Sent: Fri, March 26, 2010 5:46:13 PM
Subject: [NavList] A navigation exercise

Time again for another navigation exercise from places far afield from land.  For this one, we'll pretend I don't have much of a clue where i am or what time it is.

 

For the following problems assume the following.  IC -0.8' arc, height of eye 106 feet, T/P is 94 deg F, 1007 MB, ZD-6

 

 

While sailing  near the Chagos Archipelago a LAN observation was made on board a ship on 24 March 2010.  The star starts to hang when the watch says its 13h 18m and an Hs of the lower limb is recorded at 81 degrees 34.7' as the navigator faced north.  What is your best guess for Latitude at that time?

 

It was near calm so not much headway was made.  A bit after 1600 local time, a lunar distance observation was made between the sun and the moon.  The following observations were made in the order listed.

 

Sun LL Hs 45-29.8'

Moon UL Hs 23-33.4'

 

Ds 102-44.6'

 

Sun LL Hs 44-10.8'

Moon UL Hs 24-23.9'

 

What is the approximate UTC?

 

Have fun

 

Jeremy