Ships' Clock: Astro

[timbartlett]

Most of us on this forum don’t teach astro nav, write books on the subject or make instructional videos.

If we did, we might have to consider ourselves fair game when making ill informed or misleading statements, presented as the fruit of expert knowledge....

I somehow get the feeling that this is intended to be a dig at me, but if it is, I am afraid I am completely mystified as to what I am supposed to have done wrong.

If you've got a complaint about something, let me know (preferably in private, so that I can check it and discuss it with you if necessary without it degenerating into a public row) and if you're right and I'm wrong, I will do my best to put it right.

 

[JayBee]

Really, really final thought...

OK Tim, the devil is in the detail. It's the detail that confuses people who are trying to understand what is going on IMO.

Definitely not getting at you personally, or anyone else. Sorry if you took it that way.

I have noticed a deterioration in my own on-line manners since beginning to frequent the Lounge.

Note to self: stay out of the Lounge.

 

[nonitoo]

And it was all going so well too............................ ?

Tom

 

[Heckler]

I don't think so, but as I said, always willing to learn, particularly from a Master Mariner!

http://en.wikipedia.org/wiki/Time_zone

"A time zone is a region of the earth that has uniform standard time, usually referred to as the local time. By convention, time zones compute their local time as an offset from UTC (see also Greenwich Mean Time). Local time is UTC plus the current time zone offset for the considered location."

A 'noon' sight, will be at 'local time' - the same 'local time' as "Mer Pass". If the above Wikipedia is correct, an observer could be anywhere in a particular time zone at 'noon local time'.
Hence my argument that it is inaccurate for Longitude.

A GMT timepiece, will only show time at Greenwich, which may be unrelated to how much 'westing' or 'easting' has occured.

'Ships local timepiece' remaining uncorrected until it changes at the next time zone. On yachts, conveniently done at about midday, when watches are least affected, by a +/- 1 hour.

"ex MN Master Mariner and 1st Class Maritime Pilot"
Wow
amazing what peeps put in their bio!
Remember years ago, in Rhyl Harbour, a chap came up to us and started off, "As a Master Mariner" My mate John said to me "Master ******" is what the rest call him! Stuck in my mind ever since!
Stu

 

[alant]

I take it then you are unfamiliar with basic astro nav?

In the morning you take a sight and draw a position line. This will be roughly North-South but not in itself enough for a longitude.

At Noon you take another sight which gives a position line exactly East-West.

You then transfer the first position line forward using the difference in the log readings at the morning and noon sights plus estimated current effects. Where the transferred position line crosses the noon lat is your fix i.e. lat & long.

In the evening you take another position line and transfer the noon lat forward in the same way. Thus you get 2 fixes a day.

Of course there are inaccuracies introduced by use of DR to do the transfer but for ocean navigation purposes it is generally adequate.

A 3 or more star fix will be more accurate - if you can get one. Also when approaching land you can use position lines in other ways. e.g. when approaching your destination you can wait until the sun azimuth is at right angles to your destination then take a position line and sail down it.

Perfectly familiar with basic astro nav, its just from the tenure of your previous post - when we were discussing longitude/noon sights, thought you had a different method for finding longitude than the conventional transfer position method usually adopted (as explained).

 

[alant]

"ex MN Master Mariner and 1st Class Maritime Pilot"
Wow
amazing what peeps put in their bio!
Remember years ago, in Rhyl Harbour, a chap came up to us and started off, "As a Master Mariner" My mate John said to me "Master ******" is what the rest call him! Stuck in my mind ever since!
Stu

Anyone who's a MM, aces an RYA Cert big time, so, If you've got it, why not flaunt it!
Its been earned!

 

[LittleSister]

I also guess that, if you are in the "routine", it would stand you in good stead if the various GPS systems on the boat failed.

But not if you were relying on the GPS as your timepiece, as some were suggesting!

 

[Heckler]

Anyone who's a MM, aces an RYA Cert big time, so, If you've got it, why not flaunt it!
Its been earned!

Why would I care if Id been "Aced"?
I sail my boat from A to B, get there and back OK, dont need to collect badges like a Boy Scout. Didnt see any point in that either!
Its a bit like the wassocks we see sometimes here, Fast Track Course, vee important are they!
Stu

 

[nonitoo]

Why would I care if Id been "Aced"?
I sail my boat from A to B, get there and back OK, dont need to collect badges like a Boy Scout. Didnt see any point in that either!

Stu

I'm sure you do it very well.

It took me 11 years to get my MM ticket and I certainly don't consider it "collecting a badge". It was a professional qualification I required to progress my career.

Is it so terribly wrong/irrelevant to put it in your bio when this is essentially a marine forum where, as far as I am concerned, the wider the knowledge base the better it is for all ?

Of course I exclude the Lounge !!

Tom

 

[Heckler]

I'm sure you do it very well.

It took me 11 years to get my MM ticket and I certainly don't consider it "collecting a badge". It was a professional qualification I required to progress my career.

Is it so terribly wrong/irrelevant to put it in your bio when this is essentially a marine forum where, as far as I am concerned, the wider the knowledge base the better it is for all ?

Of course I exclude the Lounge !!

Tom

Yep, very commendable BUT why put it in a bio? Surely a well presented/argued post is what its all about. The fact that someone is a MM does not make the post or argument better - does it?
Stu

 

[snowleopard]

Perfectly familiar with basic astro nav, its just from the tenure of your previous post - when we were discussing longitude/noon sights, thought you had a different method for finding longitude than the conventional transfer position method usually adopted (as explained).

Don't see how you could have reached that conclusion after I had said

"All my fixes were done using sun-run-sun: morning, noon & afternoon."

 

[smartcom]

For easy astro calcs, you could look at one of the software packages available, such as WinAstro (www.winastro.co.uk)

 

[Lady Campanula]

For easy astro calcs, you could look at one of the software packages available, such as WinAstro (www.winastro.co.uk)

But that would assume Tim Thornton knew how to reduce astro sights better than you or I.....

And certainly more than half the interest comes from doing it, and understanding it, yourself.

Gawd save me from earnest geeks!

 

[charles_reed]

May I ask the panel for opinions, use and experience of a ships' clock?

Are there any examples of commonly available, reasonable cost, accurate, (digital?), timepieces?

Or is common use to have any old thing and log daily calibration versus a radio time signal. If so, what is a commonly used time signal.

Hopefully, you get my drift

Many thanks.

David

I always use the GPS!!

 

[reginaldon]

May I ask the panel for opinions, use and experience of a ships' clock?

Are there any examples of commonly available, reasonable cost, accurate, (digital?), timepieces?

Or is common use to have any old thing and log daily calibration versus a radio time signal. If so, what is a commonly used time signal.

Hopefully, you get my drift

Many thanks.

David

I don't know about your drift but there certainly seems to be a bit of 'Thread Drift' here!

 

[snowleopard]

There are four possible reasons I can think of for using astro -

1. You need to because of an electronics failure

2. You're doing it as practice in case it ever becomes necessary

3. You're doing it as a hobby

4. You're doing it for an exam

In the first two cases, there's a fair chance that a failure taking out your GPS could affect a computer as well so you need to be able to do it with pencil & paper

In the third case, what's the point in getting a computer to do most of the job for you?

And in the 4th case, they won't let you use the computer.

 

[Lady Campanula]

There are four possible reasons I can think of for using astro -

Just reminded me, thanks....


"If all be true that I do think, there are five reasons we should drink: Good wine -- a friend -- or being dry -- or lest we should be by and by -- or any other reason why."

 

[Danny Jo]

Brilliant thread - now how does one print it?

This thread has everything - anecdote, instruction, debate, humour and agro - and not too much agro either. For me it is the kind of thread that makes it worth putting up with Scuttlebutt's excruciatingly slow load time, and the slings and arrows of outrageous forumites.

The icing on the cake would be someone describing a simple method of saving the thread to a Word file, or somesuch, to read on the boat when skulking, stormbound, in a harbour during the summer.

 

[Cruiser2B]

The icing on the cake would be someone describing a simple method of saving the thread to a Word file, or somesuch, to read on the boat when skulking, stormbound, in a harbour during the summer.

I'm sure some computer geek will give a better method, but you could click the reply button and the whole thread will be below the reply window without the annoying pic's and avatars; select the lot, copy and paste into word.

 

[snowleopard]

I'm sure some computer geek will give a better method, but you could click the reply button and the whole thread will be below the reply window without the annoying pic's and avatars; select the lot, copy and paste into word.

There are a couple of options in the Thread Tools menu: Printable Version will give you something you can cut and paste into Word. email will let you send it to your mailbox.