# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

### Compose Your Message

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Silicon Sea : Leg 69
From: Yves Arrouye
Date: 2001 Apr 09, 18:55 EDT

```Hi,
Here's my navigation. I have to thank Ed Falk for his sample leg
(http://www.best.com/~falconer/Navigation/) which was a great help (the
plotting sheets were nice, especially since my local West Marine didn't
carry the real ones). I used as much of the online government calculators I
could find, and included links to them. They're really nice. I'll do other
legs using paper after I get the books :)
> Chart(s): Plotting Sheet
>
> Dead-Reckoning problem     Leg 69  040401   Test your knowledge!
> ----------------------     ------  ------   --------------------
>
> The last DR position was(10d 27.9'N  52d 26.4'W) on 18/05/2000 @
> 12:30:01UT.
> Our Speed has been 10.7 Kts, TC 288.9d Var 19dW. Dev 1.5dE.
> Current Set
> 285d
> Drift 0.5Kts.
Using a transverse table (http://pollux.nss.nima.mil/calc/traverse.html), we
use:
Course angle: 288d 54'
Distance: 107 (10.7 * 10 hours, which includes an approximation for the
current)
and we find:
Difference of latitude: 0d 34.66'
Departure:                 101.23
which gives us:
Difference of longitude: 1d 43.1' (102.23 * cos 11)
Our DR position is:
1  11               1
10d 27.9'N          52d 26.4'W
+     34.7'         +  1d 43.1'
----------          ----------
11d 02.6'N          54d 09.5'W
We'll use an AP of 11d 00.0'N and 54d 00.0'W.
> On that evening we take the following sights:
>
>         Body            UT                                      Hs
>
>         Sirius      22:15:30                    28d 16.3'
>         Spica           22:17:02            42d 20.6'
>         Avior           22:19:00            15d 55.3'
>         Bellatrix       22:19:45            13d 26.5
>         Dubhe           22:20:12            37d 56.1'
>
>
> 1)  What is our FIX position?
> --  -------------------------
Instead of a paper Almanac, I used the celestial navigation data from the
U.S. Naval Observatory at http://aa.usno.navy.mil/ (then click on Data
Service and then click on Celestial Navigation Data). This page gave me Hc
and Zn directly, which I feel is cheating. Is there a page there that would
give me just the almanac data?
Star:        Sirius          Spica          Avior      Bellatrix
Dubhe
UT:        22:15:30       22:17:02       22:19:00       22:19:45
22:20:12
---------      ---------      ---------      ---------
---------
Hs:         28 16.3        42 20.6        15 55.3        13 26.5        37
56.1
+/- ie: -       2.5    -       2.5    -       2.5    -       2.5    -
2.5
-dip:   -       2.9    -       2.9    -       2.9    -       2.9    -
2.9
---------      ---------      ---------      ---------
---------
Ha:         28 10.9        42 15.2        15 49.9        13 21.1        37
50.7
+/- ro: -       1.8    -       1.1    -       3.6    -       3.5    -
1.2
---------      ---------      ---------      ---------
---------
Ho:         28 09.1        42 14.1        15 46.3        13 17.6        37
49.5
GHA:         109 29.3         9 51.2        86 01.4       130 33.5        46
01.0
Decl:   -   16 43.2    -   11  9.8    -   59 30.9         6 20.8        61
45.3
---------      ---------      ---------      ---------
---------
Hc:         28 32.3        40 51.1        14 56.3        14 21.1        38
54.8
Zn:           243.9          115.4          196.2          273.8
4.8
Int:         23.2 A
Big intercepts! Wow. If I plot these, I end up near 10d 53'. Using this as a
new AP, I get:
Star:        Sirius          Spica          Avior      Bellatrix
Dubhe
---------      ---------      ---------      ---------
---------
Hc:         28 05.1        42 10.1        15 37.1        13 18.0        37
59.6
Zn:           244.8          115.1          196.7          274.2
4.2
Int:          4.0 T          4.0 T          9.2 T          0.6 A
10.1 A
Much better intercepts. The fix reads 9d 50'N 53d 00'W.
> |2)  What is the TC and distance to Barbados(13d 10.0'N  59d 20.0'W)?
> --  ----------------------------------------------------------------
From 4mulas.txt (an attachment to
sailing:
Fix L1:           9 50.0'N          53 00.0'W
Destination L2:  13 10.0'N            59 20.0'W
--------           ---------
Diff.:            3 20.0'N           6 20.0'W
l = 200.0'N      DLo = 380.0'W
1/2 l:    1 40.0'
+ L1:     9 50.0'
---------
Lm:      11 30.0'
1) p = DLo * cos Lm
= 380 * cos 11 30.0'
= 372.37 nm
3) tan C = p / l
tan C = 372.37 / 200 = 1.86
C = 61.75 = 61 45.5'
Thus the course is (360 - 61 45.5') = 298 degrees.
2) DLo = p / cos Lm
= 372.37 / cos 11 30.0'
= 379 nm
> |We continue sailing maintaining the same speed and True
> Course with an
> overcast
> sky. Then, with the navigator on deck waiting for an opening for a Sun
> shot, we
> see a spot of land on the horizon ahead. It is 20/05/2000 @
> 12:13:00ZT.
>
> 3)  What is the DR position?
> --  ------------------------
What is a good resource to convert from ZT to UT given one's lat/lon?
> 4)  What day of the week is this?
> --  -----------------------------
According to my calendar, it's a Saturday..
```
Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)