Originally Posted by GoSailing
Thanks Snowpetrel, got it, Lat and Dec the same then you add; Lat and Dec different then Dec is treated as a negative number.
the concise tables is my next goal. They look confusing but it's just like everything else, once you do it a few times, the mystery soon disappears.
What part of the Southern world are you in?
I'm in Tasmania, Australia
. Not a bad part of the world to live, though not quite enough snow for my liking, But some great sailing, walking and kayaking, look up Port Davey or Wineglass Bay.
Snow Petrel I in Port Davey
The way you deal with north/south works fine but is slightly different to how it's more commonly done. your results will be the same but if you are comparing notes you will have slightly different workings. I don't look at if dec or lat are the same or contrary, I just call Lat and dec negative if they are south, and positive if they are north, and let the maths do it's work.
EG your system: dec N, lat S you would call dec- and Lat+ whereas I would call Dec+ and Lat-. End result the same, but it's easier to spot a mistake if you are more consistent with rules across all calculations. This was more important in the "good"
old days when we did everything by hand/calc. Nowadays with gps
and chartplotters it's not so critical, so you find older professional navigators are very systematic and use rules and follow them religiously, not because they can't take the shortcuts, but because it helps prevent mistakes
, and makes it easier to spot them when
they occur (and they still do! the difference between a novice
navigator and a experienced one is not about not making mistakes
but in the ability to spot them). The N/S convention is one of these Rules and is how I spotted your initial mistake.
If you get stuck on the concise tables send me a PM, the examples in the amanac aren't the best to work off. The tricky part is splitting degrees and minutes. You Round the whole degrees up or down, but leave the minutes the same. It seems weird to do, but it works. Also the DRLong needs to massaged to give a whole LHA, so you can get some pretty large intercepts. A useful Proforma is here
Though I prefer not to use proformas for my workings, they are handy for learning.