Assume (Knowing where you aren't)

[NigeCh]

Assume (Knowing where you aren\'t)

Assume that all you've got left is a wristwatch (say a Casio set to UTC) and charts. How do you know where you are? ... I hope that Tom Cunliffe might join in this about to be thead as it might do away with his useless Celestial Navigation book.

What's your Lat and Long to the nearest 10 miles?

 

[iangrant]

Re: Assume (Knowing where you aren\'t)

If it's two thirty you are proably in the dentists.

Sorry!

Ian

 

[NigeCh]

The whole question ... or more info

Let's assume that we are somewhere anywhere on the seas. Let's assume that all the electronics have failed and that the sextant has fallen overboard together with the last handheld GPS. All we've got left are the charts and a wrist watch set to UTC.

By using our eyes and our wrist watches and knowing the analemna formula how do we know EXACTLY what our Lat and Long is?

There are no prizes for answering this. I was told somewhere else that it was a stupid question, but for those of you who equally do trans-ocean passages, I don't think that it is a stupid question. I've worked out a method using Mk1 eyeball and a watch that will locate you anywhere between the arctic and antarctic circles.

Can you work out the 'simple' wristwatch and eyeball method that will tell you where you to within 15 miles?

 

[alex_rogers]

Re: Assume (Knowing where you aren\'t)

I think 10 miles is impossible but something like 60 miles might be achievable.

Without a sextant you'd have to make up some kind of quadrant to measure angles above the horizon. If you could measure to within one degree you'd be 60 miles out but you might do better than that and get around 30 miles.

If you can use you're quadrant at night ( no torch?) you might manage to take sights of the pole start for latitude. If you can't, you'll have to use the sun at noon. The problem with the sun is that you need to know the declination ( normally from the Nautical Almanac ). This doesn't change much from year to year and there are some tricks to estimate it but if you didn't memorise these before setting off you're stuck.

Finding longitude is probably harder, you'll need to estimate the time of local noon to within something like 4mins to be within 60 miles ( at the equator ). Taking midway between sunrise and sunset with a few other measurements as the sun goes up and down might give you something like this accuracy.

If you're lucky enough to have a copy of Emergency Navigation by David Burch as well as the watch and charts then you'll be in much better shape.

Alex Rogers
<A target="_blank" HREF=http://www.YachtsAtSea.com> www.YachtsAtSea.com </A>

 

[Badger]

A few things....

1.You definitely need to get out more.
2. Tom's book is not rubbish himself and the man himself is a legend
3. I only wear Rolex
4. have you thought about Golf ?

 

[Twister_Ken]

More info pl.

Do I still have a functioning log, and something which will give me a goodish estimation of local currents?

Or a very good and powerful pair of bins and an ABC Guide to air travel?

PS - is the sky clear and is there a working compass aboard?
<P ID="edit"><FONT SIZE=-1>Edited by Twister_Ken on 05/11/2002 14:48 (server time).</FONT></P>

 

[ghostwriter]

Re: More info pl.

word has it that it involves some howling at the moon , but nobody can confirm -so far- if an ample portion of Merlot is helpful or not.

on the other hand , bare with Nige , it wouldn't not be the first time that he leebows himself out of a seemingly impossible position , and lest we forgot....those guys in the Pacific only needed to look at the stars , look at the sea and that was about it

 

[alex_rogers]

Re: More info pl.

They also detected the Pacific swell under the wind waves by dipping their testicles in the water - bizarre but true.

Alex Rogers
<A target="_blank" HREF=http://www.YachtsAtSea.com> www.YachtsAtSea.com </A>

 

[Gunfleet]

Re: More info pl.

Reassure me they were still wearing them.

 

[Guest]

Re: More info pl.

Not necessarily

My Wife regularly removes mine.

Geoff W

She's wonderful really.

 

[sailbadthesinner]

Re: ....BER DUM TISH nm

nice one

Come on brain.get this over and i can go back to killing you with beer

 

[jimi]

Re: Assume (Knowing where you aren\'t)

Ok then, we'll dump you somewhere with a satellite phone,watch & chart. You tell us where you are and we'll only come and get you when you pinpoint your position within 10 miles.How long do you think you'll be there?

 

[Cornishman]

Re: Assume (Knowing where you aren\'t)

Please correct me if I am wrong, but it sounds to me as if you have lost the plot!

 

[tcm]

Re: Trick question

No, as he said, you have nothing at all except the charts and the watch. No log, compass, steering or anything at all.

A: Pore over the charts carefully until you find an inlet called "shit creek" and you are right there at the end, along with many others, all with liferafts and no paddles...but according to the watch...the beachbar is just about to open!

 

[NigeCh]

I lost the plot years ago ...

then I took up sailing the seas.

The question that I posed is and isn't about coastal cruising, it's about how you percieve the question. Perhaps the question would have been better posted on Yaching World's forum whch is all about sailing rather than here which seems to be all about marina bound sailing.

I think that I'm in the wrong place ... I thought that here was about sailing - But obviously it's not.

 

[Opinionated]

Re: Assume (Knowing where you aren\'t)

Presumably, if nobody can answer your problem correctly, you will have been able to confirm what you always knew - you are much cleverer than everybody else, and you have been able to show us!!

Congratulations in advance, from a confirmed dunce!



IMHO, of course.

 

[NigeCh]

All you\'ve got is ...

a wrist watch, Mk1 eyballs and a laptop computer.

I'd quite happily have you as navigator on another transat as you are this thread the only person who seems to know what I'm talking about.

 

[NigeCh]

Catch 33

I'm no cleverer than anyone else ... all I did was to ask a simple question ... Judging by the sidestepping responses it seems that nobody is prepared to propose solutons to that question.

Yes, I've solved it. Why? Because I sail beyond either both VHF/DSC's horizons .. How about you?

 

[jamesjermain]

Re: Assume (Knowing where you aren\'t)

I suspect you might be able to do something by timing sunset and getting a very rough midday altitude, but my astro is far too rusty to say what. I would also have to hope not to drift too far between one eve4nt and the other If I had a decent watch with hands, I could, of course, determin south and then shape a course such that I would get sufficiently close to land to be able to locate myself.



JJ

 

[NigeCh]

Close ...

JJ,

If you take sunrise and sunset and the figure of 8 analemna you can plot yourself to within 1480 metres +/- 20 seconds on the watch when you take the time.

With sunrise alone you can still estimate your position to within 6 miles. With a real noon setting (and a few mathematical corrections) you can get t down to 1.5 miles. If you add the earth's defraction at all points on the globe you can get the error down to and average of 420 metres.

... Mk1 eyeball and a stopwatch set to UTC