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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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