AstroNav - using a calculator or laptop

[webcraft]

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I struggled for months to come to terms with Astro (maths not being my strong point) and found that quite apart from the theory the actual plotting on a small boat with no proper chart table could be more difficult than taking the sights.

The easy answer would seem to be to concentrate on becoming proficient at using the sextant then plug the results into a calculator or laptop. A small netbook will do all the calulations using free software. Programmable calculators with the software loaded seem to be a lot more expensive, but they would of course use a lot less battery power. Does anyone have any recommendations?

- W

 

[jdc]

JavaScript?

Well I do, but it's peculiar! It might suit you however according to your avatar; as a web developer you'll be able to do it easily.

Use a mobile 'smart-phone' like an I-phone or Nokia N series or any Windows Mobile or Pocket PC or an 'I-pod touch', and run the sight reduction and plotting application in JavaScript. It works fine since JavaScript is a sort of Esperanto for computer calculations, and so works on a netbook equally well. Where this breaks down is that (i) I wrote my JavaScript programme myself so it's quirky, and (ii) if the smart-phone is working then so is a back-up GPS anyway (all smart-phones today also have built-in GPS) and this doesn't quite satisfy the inner purist.

This post doesn't directly answer your quest for a programme recomendation, but I could PM mine to get you started if you like.

 

[Robin]

.
I struggled for months to come to terms with Astro (maths not being my strong point) and found that quite apart from the theory the actual plotting on a small boat with no proper chart table could be more difficult than taking the sights.

The easy answer would seem to be to concentrate on becoming proficient at using the sextant then plug the results into a calculator or laptop. A small netbook will do all the calulations using free software. Programmable calculators with the software loaded seem to be a lot more expensive, but they would of course use a lot less battery power. Does anyone have any recommendations?

- W

I'm sure they are not still available but I had (might still have even amongst the piles of stuff from the old boat if I look) a £50 Casio SX50 or similar programmable calculator which I programmed with Sun, moon and star sights as well as other programs like course to steer over multiple tides, VMG calculations etc. Years ago PBO published over many months the programs, written in 'basic' and all the almanac data calcs well into the 21st century. I still have the program data because I copied it into a book in case I needed it. Do modern calculators still use 'basic'? You can probably tell I'm a user not a programmer!

On my spare (boat) laptop I have an astro program I downloaded free from a New Zealand website, quite good but it only does sun sights not moon and stars. Power consumption isn't really a problem because it doesn't take long to run the sight on the battery and switch off, then re-charge when power is available to spare.

 

[snowleopard]

I think the first criterion has to be - if your GPS goes down, are you relying for your astro on anything that is likely to go down at the same time?

 

[nmeyrick]

Try looking at pocket stars:

http://www.nomadelectronics.com/

You can download the demo version free, I think it was about $20 to unlock and there are versions to run on smartphones, pda's or laptops.

I agree with Snowleopard that if I were using a sextant as back up navigation I wouldn't want to be reliant on technology to be able to make sense of the readings, and I guess if you rely on the technology when it is there you will develop less facility with the old fashioned methon for when you do need it.

That said I decided that this would be useful for practicing whilst developing familiarity with using the sextant, and also for verifying the answers I get from doing manual calculations. I have the PDA version working on an old windows brick smartphone and I'm sure you could pick up one of these or an old PDA second hand for not many beer vouchers

 

[Porthandbuoy]

Years ago PBO published over many months the programs, written in 'basic' and all the almanac data calcs well into the 21st century.

That's what I developed my spreadsheets from. Started off with a Psion II Organiser, then a Psion LZ64, and finally Excel. Get the spreadsheets here:-
http://www.4shared.com/dir/31216587/ad3b16e1/sharing.html

As others have commented, electronics are useful, but you need to know what to do with paper and pencil when the batteries go flat.

 

[jwilson]

I think the first criterion has to be - if your GPS goes down, are you relying for your astro on anything that is likely to go down at the same time?

Agree entirely, have twice been on boats deep sea where almost everything electronic has stopped working through excess salt water sloshing around inside hull: these days astro is a "break glass in emergency" thing, and you don't want to then be relying on something electronic working as your last resort.

 

[actionoptics]

webcraft sight reduction table

Try this www.celnav.de/sightred.htm

 

[timbartlett]

Here's another vote for using Sight reduction tables.
Why make life difficult and error prone by messing about with computer programmes when you can get a perfectly good answer without all the aggro just by looking it up?

 

[snowleopard]

Agree entirely, have twice been on boats deep sea where almost everything electronic has stopped working through excess salt water sloshing around inside hull

Another problem is lightning. One strike can fry all your electronics. Then there's failure of the power supply - a faulty alternator can be a serious problem on a long passage.

 

[webcraft]

Another problem is lightning. One strike can fry all your electronics. Then there's failure of the power supply - a faulty alternator can be a serious problem on a long passage.

I already have almanac and javascript calculators for the PC, but I would prefer a battery powered calculator - laptops will eventually run out of charge if the boat's 12v system is dead.

Re. the question of lightning strike - I guess again a calculator kept in a Farady cage of some sort would be the answer. Anyone got any suggestions?

It is very easy to say just learn how to do it manually, but I spent hours and days and weeks and a fair bit of money doing a correspondence course, and aat the end I could just about do a sun-run-sun but it took me several hours to calculate and plot it. I am good at a lot of things on a boat, but Astrocalc is not one of them.

- W

 

[sarabande]

Faraday cage. Oven or microwave on board ? Old fashioned toolbox ? Flattish biscuit tin ?

I'm not sure about earthing the 'cage' or wrapping the calculator in insulating plastic, though

 

[Robin]

I already have almanac and javascript calculators for the PC, but I would prefer a battery powered calculator - laptops will eventually run out of charge if the boat's 12v system is dead.

Re. the question of lightning strike - I guess again a calculator kept in a Farady cage of some sort would be the answer. Anyone got any suggestions?

It is very easy to say just learn how to do it manually, but I spent hours and days and weeks and a fair bit of money doing a correspondence course, and aat the end I could just about do a sun-run-sun but it took me several hours to calculate and plot it. I am good at a lot of things on a boat, but Astrocalc is not one of them.

- W

Put the calculator in the oven (cold not at gas mark 6), you could do the same with a handheld GPS and box of AAs too!

When I was still fresh from understanding how to do it manually with tables, I made up a set of my own sight forms along the lines of do this, write it here, look up this, right it there etc. Real idiots guide stuff but it still worked for me several years later when I tried it.

 

[webcraft]

Put the calculator in the oven (cold not at gas mark 6), you could do the same with a handheld GPS and box of AAs too!

Does this actually work? We don't have an oven on board but while cowering in a lightning storm and 40 knots of wind off Porto Santo I once passed some time stuffing the HH VHF, HG GPS and satphone into a ryvita tin. I was never sure if it would have protected them in the event of a direct hit.

- W

 

[timbartlett]

It is very easy to say just learn how to do it manually, but I spent hours and days and weeks and a fair bit of money doing a correspondence course, and aat the end I could just about do a sun-run-sun but it took me several hours to calculate and plot it. I am good at a lot of things on a boat, but Astrocalc is not one of them..

I can sympathise, to some extent: I had a blank spot about astro when I first tried to learn it ... then I had a different instructor, and all of a sudden I couldn't see what the problem was!
I wouldn't like to say that I could succeed wheer your correspondence school failed, but I would be fascinated to know where the problem lies. I bet it's not the "maths" -- because, to be honest, there isn't anything more complicated than is involved in checking your change when you've bought something.
Is it:-
(a) knowing what to do next
(b) knowing where to find the information
(c) adding and subtracting in degrees and minutes
(d) turning the answers into a position

 

[snowleopard]

It is very easy to say just learn how to do it manually, but I spent hours and days and weeks and a fair bit of money doing a correspondence course, and aat the end I could just about do a sun-run-sun but it took me several hours to calculate and plot it.

As has been said here several times, the key is a good sight reduction form. All the ones you find in text books are over-complicated because they allow for Northern or southern hemisphere, summer or winter and all the heavenly bodies. Reduce it to Sun, Northern hemisphere and summer and it's all much simpler. Then you can mark all the 'same name' pages in the sight reduction tables so you're not searching for the right page all the time. Simples.

 

[Robin]

Does this actually work? We don't have an oven on board but while cowering in a lightning storm and 40 knots of wind off Porto Santo I once passed some time stuffing the HH VHF, HG GPS and satphone into a ryvita tin. I was never sure if it would have protected them in the event of a direct hit.

- W

I haven't personally put it to the test but had heard it given as good advice. If you think about cars where the occupants are fully protected from lightning strikes by the metal bodywork the principle is the same. As I understand it lightning simply takes the shortest route to earth and jumps any inconvenient gaps like unplugged aerial or supply leads and so on but it is unlikely to go searching an oven to see what is inside that isn't connected to anything.

Lightning is frightening! We were in a really bad storm mid-Channel once with it striking the sea all around us and close enough to smell ozone. I had shackled a length of chain from cap the shrouds and trailing in the water but who knows if that would have worked or not. Fortunately we were headed south and the storm was headed north so we cleared the worst of it quickly. I did put the handheld VHF in the oven along with the GPS, which was an easily unplugged one and the Decca (it was a few years back!) which was showing us doing off the clock speeds backwards anyway. We were also in the shipping lanes just to add to the fear factor.

 

[JayBee]

Using sight reduction tables like AP3270 and just following the steps by rote works OK and doesn't really need any maths skills; just a good sight form, as has been said before.

However, I think it's useful to have some understanding of what the numbers mean in terms of the observer's position on the earth and the real and apparent motion of the sun, stars, etc. For most people this is probably a bit more difficult than the maths.

A good mental picture of what's going on adds a LOT of satisfaction to the process, and it makes planning sights and troubleshooting any errors much easier.

 

[Skylark]

Practice, practice and practice

Keep struggling..............until the proverbial penny starts to drop.

Do you require "instruction" or can you "self study" with a good text book?

The Adlard Coles Yachtmaster Ocean is a good self-study guide, IMHO.

Once you can draw, label and understand the PZX triangle and hour angles you're almost there.

Sight reduction of the sun, moon, planets and stars follow roughly the same process with only small differences. Buying copies of an Almanac and AP3270 vol 1 and 2and/or 3 helps.

I agree with other posts that it's better to develop your own style of sight reduction for the various heavenly bodies. All of this should help you to easily determine if the intercept is towards or away from your CP etc etc.

I can well imagine a position to three significant decimal places from a PC being miles out. Better to be "roughly right" than "precisely wrong" as you build experience.

I'm very much in my own astro infancy and I'm determined to keep practicing until my fixes are reasonably accurate and consistent. Fortunately, I'm comfortable with the theory but that's because I've spent hours on it until it was clear in my mind. BTW, that's many hours after completion of the RYA course!

 

[smartcom]

The laptop is generally easier to use than a calculator, and can be used for many other tasks, but obviously is bigger and draws more juice. However our WinAstro software (www.winastro.co.uk) was used by most of the boats in the last Volvo as part of their mandatory backup system for a sextant fix - saving the weight of the almanac and sight reduction tables!
Tim