GPS Jamming

Re: GPS Jamming - alternatives?

You do know that this magazine told a writer with an article about the history and use of the sextant that they were unable to publish as it would contravene Health and Safety Regs. as it meant looking at the sun!!!


Phil
 
Re: GPS Jamming - alternatives?

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Assuming you have a sextant and a watch on board but don't know how to use the sextant, what is the best book for learning from scratch when the GPS packs in?

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Harrumph! ....Quite unintentional misinterpretation of what you asked above, and the rarified heights from which you asked it. After all, there was nothing else in your post to indicate your breadth of knowledge and deep understanding, so one 'understood' the poster to have relatively little background. So sorry your esteemed feathers were ruffled ....One of the limitations of this medium, no?

BTW, wouldn't you agree with the *content* of the reply, if not with the *context*? That'll be interesting....

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Re: Modern Station Pointer thingy....

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I agree, it's a vastly underrated aid to coastal nav. Even better if you have one of those 3 legged plotter thingies for fixing with 2 horizontal angles.

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Getting and plotting Lines of Position ( LOPs ) remains a valuable nav technique for many of us. Some are frustrated by the fiddling about required to plot 3 lines of bearing onto a chart. Old shipmasters had similar frustrations - but a bigger chart table!

Here's an old idea revamped, using today's materials, that may add a useful little 'something for nothing' to your chart desk.

Download, then print and/or copy the protractor onto thick acetate sheet ( copier or inkjet printer ). Cut away the extra material. One then plots three 'raw' Magnetic bearings obtained straight onto the protractor, aligns the 'three lines on the protractor' so they each run through their charted object, and the centre point is the fix position. Mark with pencil.....

Faster, avoids Mag to True errors, not yet in the RYA syllabus!

MonktonProtractor.jpg


A copy of the image and the text to go with it is here:

Monkton Protractor
Protractor text

Go ahead, try it. You have my permission to copy it. It's mine - but draws on several 'existing art' predecessors, including the Decca Navigator Company.

What's the 'diamond' use for? Well, that's the symbol for Most Probable Position - also not in the RYA syllabus. ( or, the Assumed Position in respect of the plotting of an astro position line on a plotting sheet )

Enjoi!

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Re: Modern Station Pointer thingy....

Sorry if I'm being a bit dim, but what's the difference between your "Monkton" protractor and the Douglas protractor that many of us were taught to use on our dazed kipper courses?
 
Re: Modern Station Pointer thingy....

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Sorry if I'm being a bit dim, but what's the difference between your "Monkton" protractor and the Douglas protractor that many of us were taught to use on our dazed kipper courses?

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In response to TonyD, not a whole lot.... except that I used to make up 30-odd acetate examples and hand them out to students on their first DS night, so we could get cracking with the coursework without waiting until everyone had got round to buying their Breton Plotter/compasses/pencil and rubber combo.

I also handed out little brown 2b pencils to everyone, exactly right for yottie chartwork - "Everyone say 'Thank you, IKEA!' "

Most of my Douglas protractors were lent to me by The Queen, and maybe one day she'll ask for them back. In the meantime, I tend to carry two of 'em in my nav bag - the 5" one I use on small scale charts, and the 10" one I keep for large scale charts.....

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Re: GPS Jamming - alternatives?

Yes,

Content was fine . . . 3 levels, quick (techno) fix, then the observed/calculated fix and finally the EP based on very basic measurements, a hierarchy, each being a fallback position when things go pear shaped at the current level of operations. Neatly expressed.

Now . . . about the easiest astronav how-to book and the sextant as a level two (emergency) reversionary backup . . . what I really wondered was if anyone had any practical experience. Several well-known long distance sailors (e.g. Tania Aebi) learned astro nav en-route - anyone here done so?

- Nick
 
Re: GPS Jamming - alternatives?

Nick - if you're far enough from shore to warrant reversion to astro when GPS goes T/U, then surely you can spare a few minutes per day to swing the ol' sky-wrench. How else do you determine the accuracy of your fixes or LOPs? IMO practice greatly improves accuracy in astronav.

Kevin
 
Re: GPS Jamming - alternatives?

The problem with using a sextant as your primary navigation instrument is that it does require you to have the exact time (not so difficult) but also all the relevant site reduction tables and up to date ephemeris. So you must buy the Ephemeris each year and store the books of tables.... Or you just use a computer programme... That's not too bad a solution.
When I started I used to navigate with a mixture of DR, Long range beacons and my sextant... Normally could fix my position by sextant within around 10 miles in non calm weather.... less accurate if it was rough. After I got GPS I would get the sextant out every year and make sure I could still pull the sun down from the deck of a bouncy boat.. Then it seemed pointless and I just got back up GPS...

The way that is worth considering is doing a noon latitude site... do not need the time - just watch the sun rising then falling... does not involve the tables etc and takes a couple of minutes to work out... If you know your latitude to some degree of accuracy then you are more than half way there... Worked for Columbus and Magellen and Cook and they did few long trips...
I learned by the Mary Blewitt book - brilliant... She makes it so easy understand.

Michael
 
Re: Modern Station Pointer thingy....

Thanks for the tip re: the Douglas protractor.

As I've got a placcy station pointer I've never thought of using the Douglas for HSA - something new every day.

BTW, I believe most of my nav equipment is also on loan from Betty - hope she never notices! /forums/images/graemlins/blush.gif
 
Re: GPS Jamming - alternatives?

Basic plan is at least 3 and probably more GPS sets on board, including one in waterproof container wrappedin bubble wrap with two sets of brand new batteries.

If time and energy permit then yes, I plan to learn Astro en-route and practice it . . . some people may not want to though, but still prefer to carry a sextant just in case the US switch the system off, terrorists jam it or big solar flares do for the satellites.

Will be taking the Cunliffe and the Blewitt books . . . but these still insist you plough your way through quite a lot of theory. I guess the real answer to 'instant' astro-nav is a program on a hand held device . . . then all you have to do is learn to handle the sextant, which (IMHO) is the easy bit.

- Nick
 
Re: GPS Jamming - alternatives?

Now that's a really useful download .ZIP file!

I've now got something to give to some friends who want an instant capability in astro, but don't want to do any work acquiring the skills.....

This .ZIP file, plus Sticky Stapylton's primer, the 'Google Earth' installer ....on a wee USB pen drive! With a couple of free IKEA pencils! Just the job for their pond-crossing.....!

Ta!

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Re: GPS Jamming - alternatives?

The Yanks have got absolutely masses of really good free stuff on their sites, including Bowditch, their version of the Admiralty Sailing Directions etc etc, but they've recently had their techies "upgrade" their site - makes it hard to find anything at the moment . Have a look at the drop down "publication" menu for the US National Geospatial Intelligence Agency.

Also, useful free stuff at US Navy Astronomical Applications Department.
 
Re: GPS Jamming - alternatives?

Webcraft might find this to his taste. I've used this annual publication over several years. It's well worth a look....

Cdr Harry Baker's 'Astro Navigation Tables 2006' available here:
Baker's 'Heavenly Bodies'

One might also be interested in the 'Comprehensive Step by Step Guide' and/or 'Programmed Casio Scientific Calculator', from the same source....

Let me quote PBO regarding this:
"The package represents astro made as easy as it can be. Thoroughly recommended."

Astro's another source of those 'yottie' perpetual squabbles. Recalling my first forays into its mysteries at Number 6 FTS, my comrades-in-arms and I were pleased to be able to plot our first 'sight reductions' on the same chart as the British Isles.....

But it did get better. Eventually, we all were able to do an 1800-2000 mile trip around the Eastern Atlantic solely on astro, and bring the 'vessel' back down a '50-mile lane' less than two miles wide, within 30 seconds of planned time, every time. At 600 knots.

....Or else!

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Re: GPS Jamming - alternatives?

Nick - sounds like a fair plan. If you're comfortable working the sextant and want to avoid all that annoying theory you should just go for one of the nav programs that do all the calcs for you. I used an earlier version of "The Cap'n" where you plug in sextant alt., azimuth and time, and it identified the body and would give you a run from the assumed pos'n and would even calculate a fix.

Kevin
 
Re: GPS Jamming - alternatives?

Nicholls Consise Guide Chapter X11 gives a thorough descroption of The Sextant how to use it and what to do with the results.

There are Casio programmable calculators around to do the hard bit but not muck use if dropped in the @oggin en route to the liferaft:)
 
Re: GPS Jamming - alternatives?

You're addressing a non issue. At the moment you are more likely to be hit by lightning than have your GPS jammed. So the best thing to do with that nice brass sextant is to bolt it to the top of your mast and lead a nice heavy wire down to the waterline.

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Re: GPS Jamming - alternatives?

Well I think it happened to me last Sunday p.m. off the N.Devon coast heading in to Clovelly. The GPS went haywire for about 10 mins. At one point my plotter was showing me "sailing" at 20 knots at 90 deg. to my actual course. The MoD had announced GPS jamming trials for Cornwall on the Saturday I believe, so I put it down to this. But now I'm not so sure. On the Monday, we passed a large warship in the same spot with landing craft scurrying back and fore...so equally it might have been them I suppose?

Anyway (horror of horrors ) I had to steer by eyeball and compass for 10 mins!!! What is the world coming to.... /forums/images/graemlins/shocked.gif

PS - fortunately was not hit by lightning though...
 
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