Sat nav the early years.

Vara

Vara

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Just been having a chat in a pub re satellite navigation.

What was the forerunner to GPS called?

The one where you had to input height of aerial and boat speed and it took about an hour to get a reliable first fix but was OKish after that.
 
The TRANSIT system was introduced by the US Navy in the the 1960's and made available to worldwide commercial use in approximately 1974, yes 34 years ago. It was withdrawn from service in the mid 1990's. The further north or south of the equator you were the fix ratio was better but close to the equator you would be lucky to get two decent fixes in 24 hours. It certainly saved my bacon once or twice trying to make landfall on low lying coastlines with rocky outcrops. Hope this helps! An Ancient Mariner. /forums/images/graemlins/confused.gif
 
Decca. Would take less than 10 min to find itself if it had a reasonable idea, maybe 20-30 mins if it had no idea. Worked fine once located and updated continually. Had one on a RIB we used for diving and it had excellent precision (ability to find the same point again) but the accuracy was a few hundred metres either way. Obviously no chartplotter, just a lat/long readout. This was a late'ish unit - 1990 Phillips AP4 I recall. Certainly good enough to find the entrance to Waterhouses harbour when a thick fog came down when we were diving off the Farnes one time.
 
Sailed across the North Sea from Tynemouth to Norway in 1988. We had Decca (or was it Loran?) on board. We fixed using DR each hour and then 'checked' it against the Decca. I couldn't see the point, if Decca was different we believed the DR, if they were the same you just felt a bit better. In reality we checked the fixes against the rigs we passed - I'll not forget the sight of those gas flares in the pitch black of a force 6 night. Magic! Came back and read in a mag that a new satellite system was coming out that could plot your position to better than a quarter of a mile. My how things have changed, I discovered 2 years ago that SWMBO was using the plotter to judge safe distances from the canal sides on our way through Holland.

Sorry, bit of a thread drift!
 
I sailed a boat which had 'Nav Sat' from Mauritius to Durban in the mid '80's. The box was the size of a desktop PC and drew considerable amounts of current. IIRC we only took a fix a day to verify DR navigation. The geoid WGS-84 was agreed in 1984, it was and still is the reference Geoid for GPS. The Satelitte system in use before that was TRANSIT and used doppler shift to calculate fixes. I am pretty sure that the old box on my trip was a transit one. Magnavox made a transit navigator and it did DR nav in between fixes that could be several hours apart.

Transit started in 1959 and only phased out in 1996 although the satellite constellation is still up there and is being used for ionospheric monitoring.

Prior to that I think the only things commercially available were LORAN and other RDF type systems
 
I know what you mean about size of receiver. In 1974, my first experience with Satnav, the signal was received on the bridge via an IBM System 7 computer (generally used in banking at that time). This was the size of a wardrobe and then fed its information to a console the size of a tallboy. Ironically the computer I am typing this on is probably a million times more powerful and a quarter percent of the size.
 
I took part in the OSTAR in 1976. Alain Colas was also entered, with the 230 ft Club Med, which was equipped with satnav. The organizers decided that it would give him an unfair advantage as it cost more than most of us spent on our boats. I was amused to receive a letter from the RWYC informing me that I could not use satnav.
 
And it wasnt too long ago the only way I could find my way from Nottingham to Blackburn was by taking sun shots through the passenger window! /forums/images/graemlins/shocked.gif Youngsters eh, now with all that Tom Tom stuff, they never had it so good!
 
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Just been having a chat in a pub re satellite navigation

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Might you be thinking about Mk 1 Astro, perchance? All the kit is still up there, and it all still works. BTW, one can/could get a fix onto the chart rather faster than 2 every 24 hours - in V-Force, the routine was 4 per hour - and it didn't draw much electrickery. /forums/images/graemlins/grin.gif

Sad auld git that I am, I still have an old Consol chart, 'cos of the good memories 'charging' about the Channel in one of the old wooden 'Windfall' yachts the Air Force kept. That chart was by far the most sophisticated bit of nav gear on those boats, and it certainly earned its keep in rough weather. /forums/images/graemlins/grin.gif
 
TRANSIT .... bloody awful !

It had a habit of bunching up the sats into one run of them and then nothing for hours ... seemed to be in a 10 - 14 day cycle.

They had no chart display - just a data display and various lines showing iterations, counts etc. so you could determine position reliability !

I was OOW on a Gas Tanker that had the big Magnavox job that was a large box on floor and then a separate display. We then had it ripped out and the smaller TV type machine fitted - we thought we were in Heaven !! Same shitey Transit though ...
 
Transit remember it well, wait all day for a satellite only to find it had too low a trajectory and fix failed. It had to be in vision of aerial for quite a while to obtain a fix. The good old days.
 
Transit Sat Nav. I sailed with what was probably the first unit to be used in the North Sea. This was on a survey ship. A four man cabin ws stripped out, fitted with air conditioning and a large rack of electronics installed. We communicated with the beast using a full size telex machine! As others have said, a fix every hour or so if you were lucky.
Satellites were in low polar orbit, and the boat's position was obtained by a running fix from a single satellite at it crossed the sky. Hence the need for accurate input of antenna height, vessel's course and speed as these factors could create errors in the calculated position as both satellite and vessel were moving during the fix calculation.
Not much use for coatal nav, but potentially very useful for ocean navigation where the only other electronic system was Omega (even worse and almost impossible to get a reliable fix from and not a small boat system). At the time nearly all vessels used visual sextant observations for ocean nav.
 
The only satnav available to civilians before GPS was Transit.
Loran, Decca, Chayka, Consul, RDF etc were/are all terrestrial systems (i.e. nothing to do with satellites). Glonass is operational (after a fashion) but post-dates GPS, and other GPS-like systems such as Galileo are not yet operational.

Transit used about half a dozen satellites in fairly low polar orbits. A receiver calculated its position from the Doppler shift -- the difference between the frequency transmitted by the satellite and the frequency received by the receiver.

The same principle is used in 406MHz epirbs, except that it is reversed: the epirb does the transmitting and the satellite does the calculating.
 
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