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andrew lyner15/07/2019 18:38:41
138 forum posts
2 photos

There are sooo many clever old fashioned tricks to navigating near the coast. I must say that I tended to be a bit sloppy about doing it 'properly' when there are three GPS receivers on board. Natch, to get a useful course over ground will always involve adding some nowse about tidal streams; a 'simple' chart plotter can take you very much the long way round on long passages.

I did my first coastal Nav course about fifty years ago and we had to do everything the conventional ways. GPS has its problems though. Whereas you were lucky to rendezvous with another boat in the old days, you stand a significant risk of bumping into it if you both have the same destination co-ordinates punched in.

Frank Gorse15/07/2019 18:56:03
27 forum posts

Quite right.one horizontal angle needs a compass bearing to give position. Two horizontal sextant angles on three objects gives a fix where the two arcs overlap and both were still in the textbooks for RYA yachtmaster not that long ago but I’ve never tried either.and shouldn’t want to have to when it really mattered.

There used to be tables of ‘dipping distances’ in Reeds (along with useful things like emergency childbirth) and I still have a copy somewhere.

Fully agree about GPS though!

Sam Longley 115/07/2019 19:06:18
727 forum posts
26 photos

My first "foreign trip" from Burnham on Crouch to Ostend was in 1969 & I missed Ostend by 9 miles (no lessons for me) I hadn't a clue where I was.

I have just returned from 6 weeks single handed cruise to the Channel islands (picking up the June 06 D day landings on the way) & just as I left, my chart plotter failed. The best part of the trip was having to manage the navigation conventionally. Especially 2 legs of approx 100 miles - part over night,out of sight of land-, wondering where on earth I would end up. The rocks around Channel Islands tend to focus the mind .

Spot on every time- So what I learned all those years ago still worked.

Edited By Sam Longley 1 on 15/07/2019 19:07:07

Sam Longley 115/07/2019 19:24:15
727 forum posts
26 photos
Posted by Frank Gorse on 15/07/2019 18:56:03:

Quite right.one horizontal angle needs a compass bearing to give position. Two horizontal sextant angles on three objects gives a fix where the two arcs overlap and both were still in the textbooks for RYA yachtmaster not that long ago but I’ve never tried either.and shouldn’t want to have to when it really mattered.

 

With the greatest respect, Are you sure about that?

Somehow I do not think that would give a reliable fix.The RYA method uses 3 compass bearings not a sextant angle If one has a sextant one has to work from a point towards the targets

One would have to lay the compass bearing line first then set the angle with a protractor or similar tool & slide it along the bearing line until it met the target. Repeat for the third point. The whole fix would be totally reliant on the first bearing, thus making the fix very unreliable. If one had a compass to take the bearing in the first place then one would continue to take bearings.

If you think about it, there is no advantage in using a sextant which is not only difficult but would produce an inconsistent fix.

Edited By Sam Longley 1 on 15/07/2019 19:27:30

andrew lyner15/07/2019 19:45:17
138 forum posts
2 photos

The RYA method uses 3 compass bearings not a sextant angle

If you have ever tried to take a fix with a hand bearing compass then you would realise the accuracy (on a rocking boat) is +/- several degrees (yes really). A Sextant angle can be measured to much less than a degree with practice. That's because you move the wheel until the two images are superimpiosed. So HSA is a very powerful tool.

I can't remember the geometry involved in using that angle to help with a fix but it's a pretty damned good method. iirc. What you see in a hand bearing compass will just NOT STAND STILL!

RYA don't expect an inshore yatchsmperson to own a sextant as everyone thinks they are for blue water trips.

Edited By andrew lyner on 15/07/2019 19:47:06

Sam Longley 115/07/2019 20:02:03
727 forum posts
26 photos

I would back the accuracy of my Sestral Handbearing compass aimed at a single point up against my sextant held horizontally, whilst trying to fix on 2 points any day.

Ian Johnson 115/07/2019 20:03:08
177 forum posts
53 photos
Posted by Clive Hartland on 14/07/2019 08:29:02:

Standard Instrument securing thread in the UK is 5/8" x 11 Tpi. Whit. form. There is another US style at 11/16 " x 11 Tpi. This is mainly used in Aircraft building, test equipment.. Also some military applications, just to be awkward I think.

I give up! I'm going to make my own standards! I had a quick Google for 5/8" to 1/4" adaptors and got loads of 5/8" x 27 tpi for microphones, but I'll still stick with my theory that 5/8" x UNC is a standard for surveying stuff , in the UK at least!

And as for acronyms, two common ones when I was on the tools were 'US' (Un-serviceable) and 'MT' (empty) usually written in chalk.

Ian

andrew lyner15/07/2019 20:04:37
138 forum posts
2 photos
Posted by Sam Longley 1 on 15/07/2019 20:02:03:

I would back the accuracy of my Sestral Handbearing compass aimed at a single point up against my sextant held horizontally, whilst trying to fix on 2 points any day.

You don't have to "fix on" two points. You adjust th sextant until the two objects coincide. It doesn't;t matter if they are jigging about.

What sort of accuracy can you rely on with your hand bearing compass and have you ever tried a HSA reading?

Sam Longley 115/07/2019 20:55:43
727 forum posts
26 photos
Posted by andrew lyner on 15/07/2019 20:04:37:
Posted by Sam Longley 1 on 15/07/2019 20:02:03:

I would back the accuracy of my Sestral Handbearing compass aimed at a single point up against my sextant held horizontally, whilst trying to fix on 2 points any day.

You don't have to "fix on" two points. You adjust th sextant until the two objects coincide. It doesn't;t matter if they are jigging about.

What sort of accuracy can you rely on with your hand bearing compass and have you ever tried a HSA reading?

You have just said something that conflicts-- that you have to get 2 points to coincide. Of course it matters if they are jiggling about. have you never tried tossing about in a swell aiming a sextant at a target. I have enough trouble aiming binoculars in a 2 metre chop, let alone aiming my sextant at 2 shore targets at once. I have to admit that my sextant does not lend itself to horizontal use, I have had it 40 years & it does not have wheel adjustment. I certainly have tried( just testing really) & given up as a bad job. Easy vertically. Lack of use in the last 20 years makes it difficult to pick up now

My Sestral compass is about as good as they get & i can get fairly good top hats depending on boat motion.I use it regularly in places like Channel Islands

To each his own- we are not going to agree- but does that matter- Of course not yes

Ian Johnson 115/07/2019 21:36:12
177 forum posts
53 photos

Ah ha! After a rummage around in my camera bag I found the 5/8" to 1/4" adaptor I made for fitting on the surveying posts. It is indeed 5/8" UNC. I can sleep easy now! laugh

20190715_200058[1].jpg

Frank Gorse15/07/2019 21:47:33
27 forum posts

Oh dear,

I am well aware that the three point fix by hand bearing compass was,and probably still is,the basic position fixing technique in traditional coastal navigation. But when I did the course at the local tech in 1980-something we also covered running fixes,doubling the angle off the bow,and other arcane stuff I can’t remember now. I’m not sure whether hsa’s were mentioned,probably not.

However,in ’Yachtmaster’ by Langley-Price and Ouvry,published by Adlard Coles,covering the RYA syllabus we read:

“If the sextant is turned so that it is held horizontally,it can be used to measure the angle subtended at the observer between two shore objects. A distance off is not obtained...........but a position circle can be plotted. Two such circles can be obtained from three landmarks,where they intersect is the fix.”

Sam Longley 115/07/2019 22:03:01
727 forum posts
26 photos

I am beginning to recall the method now. One doubles the angle & forms a triangle with 2 equal angles at the base & the top angle is  the observed sextant angle- (or is it twice the observed angle, or was the base angles each half the observed angle- cannot recall?). The base being the line between the 2 observed points. From that top point one strikes a circle through the 2 stations. But i seem to recall that one had to know which side of the stations one placed the triangles. Trial & error based on dead reckoning. Or obvious from the position of the land I think !!

Now I am going to have to find a b..y book & read it up for no other practical purpose other than reminding myself how !!!

Trouble is that reading a sextant horizontally through 2 points is almost impossibly on any small yacht in any sort of sea. The method possibly stemmed from the days of square riggers with a stable platform. There was also a special protractor for setting out the triangles. Forget the name. Will have to sleep on that one.

Edited By Sam Longley 1 on 15/07/2019 22:46:41

RMA15/07/2019 23:27:58
214 forum posts
4 photos
Posted by andrew lyner on 14/07/2019 10:41:37:

That's a shame. Language is a fluid thing and, by ignoring the recent additions, you can miss out on a lot of useful stuff. If TTFN and ITMA mean something to you, then you were part of the new wave of acronyms in the past. Stay in touch; you won't regret it. smiley

I've just got in and I see this thread has now taken a completely different direction, but I have to respond to a couple of people on here regarding my innocuous request to refrain from using acronyms.

The above quote I find patronising and unnecessary.

Neil makes a comment about my username,,,,why? It's not a posting.

On another thread someone queried what MSM meant and got a two word brusque response from another member, .....Google it'!

Another thread was started called 'Recent threads' and was closed because that was getting out of hand.

I don't understand why some people wish to try and show their 'superior knowledge' to anyone asking a simple question. Maybe they think they're impressing others by knowing something other's don't. I'm afraid it just reminds me of project management meetings we had back in the 70's and 80's when 'managers' would include as many acronyms as possible in a presentation, and if anyone dare ask what they meant, they were totally shown up as being 'ignorant'. Of course we all had a name for these people, and it wasn't an acronym! This behaviour was also picked up by the comedians of the day....too PC for that type of humour these days!

I'm all for a bit of banter.....but rudeness is quite unacceptable. This is a great forum and there's a wealth of knowledge and experience just for the asking. No one knows everything, so for the few that appear to spoil things, please stop. The original poster was pleased to share his experience at Aldi and good luck to him and I hope the final project is a success. It didn't warrant all the opinions on the product.....he didn't ask for that!

I've said my bit and I will refrain from responding to any further negative comments.

andrew lyner16/07/2019 00:11:07
138 forum posts
2 photos

"The above quote I find patronising and unnecessary."

I could say exactly the same about your complaint about using (well known) abbreviations. You are successfully using one part of the Internet so, instead of being grumpy about an alternative style of (informal) communication, why not just take it on board?

Using letters for well known phrases goes back to the very early days of morse so it's not a new idea.

I really didn't want to upset you.

Ian Johnson 116/07/2019 00:11:30
177 forum posts
53 photos
Posted by RMA on 15/07/2019 23:27:58:

I'm all for a bit of banter.....but rudeness is quite unacceptable. This is a great forum and there's a wealth of knowledge and experience just for the asking. No one knows everything, so for the few that appear to spoil things, please stop. The original poster was pleased to share his experience at Aldi and good luck to him and I hope the final project is a success. It didn't warrant all the opinions on the product.....he didn't ask for that!

I've said my bit and I will refrain from responding to any further negative comments.

Thanks RMA I tried my best to get my original post back on track! But 3 pages and over 2500 views! best £3.49 I ever spent! laugh

Ian

andrew lyner16/07/2019 00:17:54
138 forum posts
2 photos
Posted by Ian Johnson 1 on 16/07/2019 00:11:30:
Posted by RMA on 15/07/2019 23:27:58:

I'm all for a bit of banter.....but rudeness is quite unacceptable. This is a great forum and there's a wealth of knowledge and experience just for the asking. No one knows everything, so for the few that appear to spoil things, please stop. The original poster was pleased to share his experience at Aldi and good luck to him and I hope the final project is a success. It didn't warrant all the opinions on the product.....he didn't ask for that!

I've said my bit and I will refrain from responding to any further negative comments.

Thanks RMA I tried my best to get my original post back on track! But 3 pages and over 2500 views! best £3.49 I ever spent! laugh

Ian

Ian. I just found out form myself (today) that, if you put your message on the line below the verticals, it appears outside the quoted text.

And I think your laser 'level' was very good value and the same bit of tatt as the one I have! wink

TTFN

Michael Gilligan16/07/2019 06:54:33
avatar
14264 forum posts
627 photos
Posted by Ian Johnson 1 on 11/07/2019 21:48:25:

Thread mystery solved! I checked it again and paid a bit more attention this time! It's actually a very bad cast plastic M16 x 2mm pitch at 15.25 mm dia nowhere near 16mm or 5/8" diameter come to think of it! dont know

I wrongly assumed tripod fittings were imperial thread sizes like camera mounts. Although I am pretty certain I machined an adaptor for theodolite survey posts, which were used to check a massive bridge being built locally, which had a 5/8" UNC stud on top of them to accept a 1/4" x 20 camera mount many years ago.

Ian

.

Ian,

Now that this forum thread has had its 'run round the park' ...

I will, if I may, return to your first comment regarding the screw thread:

"just needs a little thread converter making from the weird 5/8" x 13tpi to 1/4" x20tpi"

.

Given that you have "checked it again" and and found another unlikely size; I think it advisable to try measuring once more ...

There is, of course, no obligation upon Aldi to use any standard thread; but if they have tried to follow convention, the most likely choice would be 5/8" x 11tpi.

MichaelG.

Michael Gilligan16/07/2019 07:02:37
avatar
14264 forum posts
627 photos
Posted by Neil Wyatt on 15/07/2019 10:03:22:

I posted this in the 'Aircraft Radio Scanner' thread - with my tongue in my cheek

I got a USB (Universal Serial Bus) SDR (software defined radio) for my laptop PC (personal computer). It cost about 16UKP (United Kingdom Pounds). I use it for meteor detection using RADAR (Radio Detection And Ranging) scatter with free software, but it will pick up almost anything you can make an aerial for, and you can switch it between FM (Frequency modulation), AM (amplitude modulation), USB (upper side band) and LSB (lower side band) or even stereo FM.

As SOD (Silly Old Duffer) says, this is a really cheap and easy way to experiment.

Neil

dont know

One relevant [and perhaps unfortunate] point being that you have therein used USB to mean two different things.

MichaelG.

JasonB16/07/2019 07:03:18
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Moderator
16561 forum posts
1765 photos
1 articles

Enough.

Go to a sailing forum if you want to play sailors and your abreviations will be known and not anoy members here.

Keep to the subject about the tripod please.

Sam Longley 116/07/2019 07:56:15
727 forum posts
26 photos

Jason

Apologies

I did try to delet the last post when i realised it was totally out of context but the edit was stopped

sorry

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