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Old 24-12-2012, 03:40   #1
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Sextant games / practice

So who is too lazy / busy to do an LOP in the morning, but still likes to get their long and lat at noon doing an all-in-one?

ie. getting your longitude by doing 3 sights 5 or 10 minutes before local noon where you note down the altitude and time. As the sun drops, you watch it in the sextant and note the time when it hits those same 3 altitudes, average the rising time and dropping time for each altitude, apply the equation of time and then calculate your long?

Only 1 person can get the lat each day, but we compete against each other onboard to see who can get the closest long. by each having a couple of minutes with the sextant before and after local noon.

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Old 24-12-2012, 19:26   #2
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Re: Sextant games / practice

I like this idea. Bravo.
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Old 07-01-2013, 12:52   #3
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Re: Sextant games / practice

Me too, sounds like an enjoyable and painless way to keep a basic level of familiarity.

If it's a bit lumpy it can be hard to get a good shot, or even to see the true horizon, at an exact time.

In these circumstances I wonder if you've tried taking a bunch of shots whenever you can snatch a good horizon, before and after LAN, and graphing the resulting altitudes, with time along the x axis?

It makes it relatively easy to discard outliers and to get a high quality interpolated curve, whose summit point represents Local Apparent Noon. This could still be done in a competition format, passing the sextant to the next person each time a shot has been snatched.

Each person would need a longer chunk of time, so it might not be practicable for more than two or three, unless you have a few cheap plastic sextants. (Also a good idea for use in rough weather, when you don't want to risk damage for non-essential use)

Obviously, using a sextant is pretty straightforward when it's calm, but the real challenge is to get reasonable fixes when it's not. And the only way to do that is to practice regularly, and I think your suggestion is a really good one.

- - - - -

I just farewelled a friend sailing off across the Southern Ocean and through Drake's passage. It will probably take him about 40 days to get home.

His Dad has spent all his life at sea and was one of the iconic navigators of his generation. He pioneered new techniques for things like LAM (Local Apparent Midnight) sunshots for polar navigation (where the graphed curve is upside down), and (IIRC) semi-horizontal sextant angles (solar/planetary/stellar distances) between the sun and Venus or Sirius...

It was sad to hear the son speak of the main challenge he expects to face on this leg (which more than completes a solo circumnavigation).

That challenge? Boredom. On a leg which includes Cape Horn...

I doubt that his dad was ever bored at sea ... at least, not until the advent of affordable black-box navigation.
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