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Old 04-08-2020, 07:11   #61
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Re: Considering ditching electronics and navigating the "old" way

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Originally Posted by barnakiel View Post
You got me interested :



How do we skip the sextant thing?


I understand the chart can be skipped too when we know how to make a plotting sheet.



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Timing sunrise and sunset. Day length giving the latitude position line (+- Nm sailed W or E) and excact time giving the line to plot longitude. Of course it works with other celestial bodies as well but needs a bit more calculations. Equinox is best spend fishing if latitude plot is essential..
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Old 04-08-2020, 07:25   #62
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Re: Considering ditching electronics and navigating the "old" way

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They did run aground with what we would now consider shocking frequency though. Turns out celestial navigation does nothing to help you avoid collisions with other ships (unless I missed that part of nautical science class at the Academy?) and does a passable but not great job of telling you where you are.
But it does as with the presumed uncertainty of celestial navigation and dead reckoning keeps you more alert of the surroundings, anyway what comes to other vessels. Wonder what makes a Navy ship to do "crazy Ivan" over TSZ without lookout? Bad charts and no fix of course are hazard waiting to happen..
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Old 04-08-2020, 08:07   #63
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Re: Considering ditching electronics and navigating the "old" way

Another way to skip the sextant is to take the time when the upper limb of the sun just disappears at sunset. Reduce that as a zero altitude sight. I suppose it would also work at sunrise except Iím never awake enough to try it.
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Old 04-08-2020, 08:42   #64
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Re: Considering ditching electronics and navigating the "old" way

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Originally Posted by TeddyDiver View Post
Timing sunrise and sunset. Day length giving the latitude position line (+- Nm sailed W or E) and excact time giving the line to plot longitude. Of course it works with other celestial bodies as well but needs a bit more calculations. Equinox is best spend fishing if latitude plot is essential..

OK.


I have not tried the latitude from day's duration, but I will try it on our next crossing.


But the longitude for sunrise sunset I have tried and I must report HUGE errors encountered. I can't tell why I got such big differences, all I know they were there - within 2 degrees or so.


I must try harder.




Which of the two methods have you tried, and how close to your position did you get?



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Old 04-08-2020, 10:04   #65
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Re: Considering ditching electronics and navigating the "old" way

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Originally Posted by barnakiel View Post
OK.


I have not tried the latitude from day's duration, but I will try it on our next crossing.


But the longitude for sunrise sunset I have tried and I must report HUGE errors encountered. I can't tell why I got such big differences, all I know they were there - within 2 degrees or so.


I must try harder.




Which of the two methods have you tried, and how close to your position did you get?



barnakiel
Neither for navigation but tried a couple of times for curiosity.
The contingency lies in the weather as the sun is not allways the where it seems to be and closer to equinox the latitude accuracy suffers a lot. Most times you should be in five to ten Nm circle, enough for open seas and to get destination visible..
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Old 04-08-2020, 16:28   #66
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Re: Considering ditching electronics and navigating the "old" way

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But it does as with the presumed uncertainty of celestial navigation and dead reckoning keeps you more alert of the surroundings, anyway what comes to other vessels. Wonder what makes a Navy ship to do "crazy Ivan" over TSZ without lookout? Bad charts and no fix of course are hazard waiting to happen..
So we should use an inferior form of navigation to make us more alert to other vessels that could be a collision hazard?

Seems that spending more time focusing on radar skills, rules of the road, and proper watch keeping would be the best way to minimize the risk of collisions, but hey what do I know. I guess in some crazy alternate universe up is down and purposely handicapping your situational awareness and requiring you to be heads down doing nav calculations for significant time periods makes collisions less likely?

I had the unique experience of having to use celestial nav exclusively on the Eagle (295' Barque) and using modern nav tools as OOD on several Coast Guard cutters. Curious what your experience as an OOD on a large ship relying on celestial navigation in crowded seas has been to lead you to the opposite conclusion as me?
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Old 04-08-2020, 16:51   #67
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Re: Considering ditching electronics and navigating the "old" way

Paper charts and el cheapo handheld GPS will get you anywhere in the world, for the moment. If the world runs out of AA batteries or they turn off the GPS network, we'll all be toast anyway...
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Old 04-08-2020, 17:09   #68
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Re: Considering ditching electronics and navigating the "old" way

Itís been quite a while since I used the zero-altitude upper-limb sunset sight. But I remember that I had to do the corrections for Hs the long way. The short corrections donít work at low altitudes. But I remember it being close enough to my GPS position that it surprised me.
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Old 05-08-2020, 07:46   #69
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Re: Considering ditching electronics and navigating the "old" way

AA batteries can be substituted with AA nicads rechargables. Shelf life > 10 years.


As long as there is glonass / beidou / gps or Galileo up there, we are set. The bad news would be some sort of solar event that could destabilise or wipe out the satellites or their ground stations.



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Old 05-08-2020, 10:19   #70
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Re: Considering ditching electronics and navigating the "old" way

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Speaking as one who made ocean passages with celestial because it was all that there was, I can say that I'm glad that I know how to do it, but I'm even gladder that I don't have to any more.

Jim

Yes! When I did a cruise to French Polynesia in 1990, we didn't have any electronic nav aids and it was very rewarding to see the islands come up right on our course and time as my sights had predicted. But lately I tried out the sextant again, and I was reminded at how time consuming it is to reduce a sight by hand. And even after a few sights, it was evident I need to do some practice to catch up!

For the cruise in 1990 I programmed a calculator (this was before PC's were common on boats) to do my sight reduction. Still had to look up and enter the Almanac info. That time is time taken away from running the boat better in all other respects, such as maintaining a better lookout, getting more weather info, sleep as needed, etc.
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Old 05-08-2020, 12:25   #71
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Re: Considering ditching electronics and navigating the "old" way

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So we should use an inferior form of navigation to make us more alert to other vessels that could be a collision hazard?
Nope, we should take a look outside instead of a screen

Seems that spending more time focusing on radar skills, rules of the road, and proper watch keeping would be the best way to minimize the risk of collisions, but hey what do I know. I guess in some crazy alternate universe up is down and purposely handicapping your situational awareness and requiring you to be heads down doing nav calculations for significant time periods makes collisions less likely?

One could think that's what they teach in Annapolis Naval Academy but obviously not in every course, anyway being handicapped, even just for practice, is a valuable lesson

I had the unique experience of having to use celestial nav exclusively on the Eagle (295' Barque) and using modern nav tools as OOD on several Coast Guard cutters. Curious what your experience as an OOD on a large ship relying on celestial navigation in crowded seas has been to lead you to the opposite conclusion as me?
Good for you. I've never crewed large ships but been the eye balling OOD of my boats since -65, ie since I was 6yrs old. Don't get me wrong, as I like modern plotters and sh*t. What I don't like is the over confidence and CAI..
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Old 05-08-2020, 13:09   #72
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Re: Considering ditching electronics and navigating the "old" way

My recollection is that there was a considerable amount of administration required to maintain the old sextant based system in addition to the paperwork required to reduce sights. For example maintaining an accurate timepiece and keeping track of it's errors.There was also the cost of maintaining a chart portfolio and regularly replacing the almanac etc.

It is a contingency item with trade offs between cost and effort versus the probability of non availability of an electronic system which can be readily equipped with adequate redundancies of instrumentation and power sources to ensure a high probability of reliable availability?
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Old 05-08-2020, 14:18   #73
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Re: Considering ditching electronics and navigating the "old" way

The cost is negligible provided you have the timepiece ...


Today the clock is the most expensive part of a basic astro nav kit!



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Old 05-08-2020, 14:39   #74
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Re: Considering ditching electronics and navigating the "old" way

Playing "what if" games about what will, or might, or could maybe fail and then assuming you can "provide sufficient redundancy" to avoid the problems is whistling past the graveyard. If one has a lightning strike which takes out every piece of electronics, or there’s a solar flare that knocks out all the satellites, one KNOWS that the equipment doesn’t work. The real danger of electronic navigation is that it’s so "easy" that most people tend to uncritically believe what it tells them. That’s why people will follow GPS map directions into impassible snow-covered roads or off the ends of docks into the water.

If one doesn’t have a method of knowing when their information might be inadequate, you’ll trust it right onto the beach. "Trust, but verify."
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Old 05-08-2020, 14:57   #75
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Re: Considering ditching electronics and navigating the "old" way

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(...)



"Trust, but verify."

Exactly. A healthy attitude in navigation and in a marriage!


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