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From: Dan Hogan (no email)
Date: Tue Jul 01 2003 - 10:15:41 EDT
On 30 Jun 2003 at 23:48, Joe Schultz wrote:
> Well, a dozen years and the rust has removed all of the paint. Here
> are my answers to the first part, followed by questions for the
> experts. I used a calculator with trig functions for the
> calculations and home-made sheets for the graphical solution (after
> locating my Speedbow, C-Thru ruler, and a metric scale).
>
> 1) L2 = 39d 39.0'N Lo2 = 154d 43.0'W via Mid Latitude Sailings
> L2 = 39d 39.0'N Lo2 = 154d 42.1'W via Mercator Sailings
> L2 = 39d 38.5'N Lo2 = 154d 43.9'W via three plotting sheets
OK
> 2) 0830:20 ZT 10SEP2002 (1830:20 UT 10SEP2002 +10). Intermediate DRs
> were plotted every four hours starting 0400 UT 09SEP2002, since we
> are in the open sea.
OK. Find a technique that works for you and stick with it so that it becomes
routine for you.
> Questions:
> 1. Are there rules-of-thumb in terms of distance limits for which I
> decide to use Plane, Mid Latitude, or Mercator Sailings?
Yes. Plane sailing use for about 50 miles and under. Mid-Latitude is accurate
for 500-600 Nmi. Mercator Sailing is accurate N & S and picks up an error E &
W when you cross the celestial quadrant of Lo 1.
> 2. Plotting sheet dL = 0.5 Nm to calculated L2, which shows my
> current ineptitude in plotting (used 10 sheets of paper to get three
> "good" plots). How close to calculated Lo2 can I reasonably expect
> to arrive with a correct plot? Note that I cheated and used dL = 2d
> 20' for the middle plotting sheet.
There will be an argument on this, but if you can plot it to within +/- one
minute of arc you are accurate. In actual practice it will vary within a 4'
circle of error. The calculated number will vary depending on the formula
used.
Also consider the width of the pencil line in relation to the size of the
plotting sheet.
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