Are the days of satellite GPS navigation numbered??

[rslifkin]

Originally Posted by Benz

I've had good success with Ritchie compasses. I don't think they cost nearly as much as the Plastimo.
You might find a used one at a consignment shop--there's tons around here.

I'll second the Richie compasses. My boat has a 38 year old Ritchie Powerdamp on the binnacle. It's easy to read, works well, and other than being swung after nearby equipment changes, it's never had any issues. Even still has the original (working) light bulb in it for night use.

[Johan Leopard51]

GPS is at times deliberately offset.

Besides time on boats we also spend time overlanding / Safari in Africa. More than once I have had our Land Cruiser physically in a town at known landmark like police station but Garmin say I’m 15 miles away.

GPS is kindly made available by US military. When they are busy with operations they can and do shift data. I think simply by changing the time stamps that public sees?

On land it was simple to see our GPS location was not on the physical road we knew were actually on. On sea, you would only have nav beacons or land marks to know the off-set.

We almost never other than over definite very deep waters on crossing cruise at night - the Seychelles nav charts are not reliable in any event - so in under 50m waters we rely on visual. Relying on GPS and charts you will bump something.

[Statistical]

Originally Posted by Johan Leopard51

GPS is kindly made available by US military. When they are busy with operations they can and do shift data. I think simply by changing the time stamps that public sees?[

That is called selective availability and hasn't been used in 24 years now. The newer GPS sats don't even have the ability to enable SA.

Soldiers have access to the military L1 and L2 channels by loading a random rotating code into the gps receivers so they can't decrypt those higher precision signals. I know because it is a bit of a pain in the ass.

GPS is at times deliberately offset.

Besides time on boats we also spend time overlanding / Safari in Africa. More than once I have had our Land Cruiser physically in a town at known landmark like police station but Garmin say I’m 15 miles away

This may have been interference or it may have been local jamming/spoofing but it wasn't from the source (gps sats). Even when SA was used it introduced a pseudo random error of up to 20 meters not 15 miles.

[Kettlewell]

Traditional sextants will remain quaint dinosaurs unless a massive EMP comes along.Then just run a DR plot until you hit land.

I still carry one onboard along with a compact set of sight reduction tables. Haven't used them in many years though. I would still need the almanac data and an accurate time, and I bet if GPS was down other things like precise timekeeping and maybe phone and satellite communication networks would be down too. However, unless one was completely unaware of where you were to begin with, there are many methods to navigate that were used long prior to celestial navigation being available and will continue to be used long into the future. For example, when one nears an island group you will often encounter land and sea birds coming and going to and from the land, there are often clouds over the island that can be seen 50 miles away, there may be a change in depths, the water color can change, there are different smells in the air, etc. I was once beating my way toward Nassau in the Bahamas on a very dark and dreary night and I could smell the island from ten miles out. Similarly, I've worked my way into tight little coves in Maine in dense fog listening for buoys and the crash of waves on rocks. I do think many of today's boaters never learned these seat-of-the-pants skills and I have heard more than one on the radio in a panic when their GPS went down.

[requiem]

Originally Posted by Johan Leopard51

On land it was simple to see our GPS location was not on the physical road we knew were actually on. On sea, you would only have nav beacons or land marks to know the off-set.

Typically this is due to the map or chart being incorrect, not the GPS position. You can see an good example* of what this looks like with China, where a pseudorandom offset is intentionally introduced. Often an easy way to check this is to compare the map view to the satellite view.

If you're using official charts they'll often have a note in the margins or metadata warning that one should use distances and bearings to charted objects instead of satnav. Fortunately I think updates to charts are slowly reducing the incidence of this.


* https://www.serviceobjects.com/blog/...maps-of-china/

[Johan Leopard51]

Also be careful of some of the Apps for ‘navigating’ that use your phone/tablet location.

In one case:
I was on anchor say 30m off beach.
Raymarine maps showed me where I was.
Garmin handheld device showed me where I was, as good as could make out on its screen..
I always cache sat images and my iPad showed me about where I was.
The marine navigation app on my iPad showed me on land…. Obv the app people stitched their maps incorrectly but when I queried they blamed iPad location accuracy. Needless to say I deleted that App!!

[Jammer]

Originally Posted by MicHughV

What happened to:

"drive down this road until you see a red shed on the right side of the road, just past the red shed is a dirt road going to the left, take a left there and go about...hmmmm.....2miles or so, until you see a farmhouse with a green roof, just past that farmhouse is a road leading to your right, but it splits in two, take the left split and pretty soon you'll come to a cow pasture on your right, you can't miss this, as it's always full of cows, drive by this pasture and take the next turn to the right, that road will zig and zag a lot, but stay on it, and eventually you'll come to a river, follow that zig zag road for another mile...or maybe two until you see a bridge, relax, you are almost there, cross that bridge and about a mile...maybe two or three, you'll come to a store with a gas pump out front, the owner's name is Zeb, from there Zeb will tell you the rest of the way....."

Proper directions given by one local to another always include landmarks that no longer exist as well as instructions to turn a certain distance before reaching some prominent feature.


"Turn left where the k-mart used to be"
"Turn right a mile before you get to the church"

[Jammer]

On a more serious note, I routinely carry a HAQ watch that is more than accurate enough for longitude and that does not rely on radio signals. They're available. Some people use cheap watches and rate them carefully.


Pilotage, dead reckoning, and radar are my preferred approaches to navigation without GPS.


A problem we face is that many of the aids to navigation from before the GPS era have been decommissioned. Most notably the radiobeacons, but also ranges, and in some cases buoys marking channels.


Hard to find a good VHF/LF/MF direction finder these days.

[MicHughV]

Back in my varsity days, I had to learn the fine art of land surveying. This included learning to use 7 figure log tables.
As I test, I was made to survey a route of several kilometers long and double back, where I had to close within a millimeter or so at my starting point.
This included a variety of triangulation fixes, etc.

Fast forward to today, where surveyors do it all by GPS....harumph.

I often wonder what will become of the planet if the GPS system , suddenly went belly up.

Some people might not be able to find their own home on their own, having become a slave to that voice in a box, telling you to turn left at the next intersection, etc.

[coopec43]

Originally Posted by Kettlewell

I. For example, when one nears an island group you will often encounter land and sea birds coming and going to and from the land, there are often clouds over the island that can be seen 50 miles away, there may be a change in depths, the water color can change, there are different smells in the air, etc. I was once beating my way toward Nassau in the Bahamas on a very dark and dreary night and I could smell the island from ten miles out. Similarly, I've worked my way into tight little coves in Maine in dense fog listening for buoys and the crash of waves on rocks. I do think many of today's boaters never learned these seat-of-the-pants skills and I have heard more than one on the radio in a panic when their GPS went down.

You have read this book?




We, the Navigators: The Ancient Art of Landfinding in the Pacific
David Lewis

This new edition includes a discussion of theories about traditional methods of navigation developed during recent decades, the story of the renaissance of star navigation throughout the Pacific, and material about navigation systems in Indonesia, Siberia, and the Indian Ocean.

[motion30]

Of all the different things I worry about or struggle with on my boat this is not one of them

[SeanPatrick]

Originally Posted by Jammer

On a more serious note, I routinely carry a HAQ watch that is more than accurate enough for longitude and that does not rely on radio signals. They're available. Some people use cheap watches and rate them carefully.

A few years ago I got a Bulova Precisionist (Model C877749) from JacobTime at 60% off. Bulova claims the watches are accurate to within ± 10 seconds per year, due to a special quartz crystal that vibrates at "eight times the frequency of a conventional quartz watch – 262,144 vibrations per second (or about 262 kilohertz)". You can still see this claim at Bulova's website.

I rated this particular watch at an extremely stable +0.2 seconds per day or about +1m13s per year. Maybe that's why it was so cheap. But that's still incredibly accurate.

The watch is bulky with a very large dial. But I get a lot of compliments on it. Sometimes because it has such a large dial and is easy to read.

It's my favorite watch.

[coopec43]

Originally Posted by Benz

I've had good success with Ritchie compasses. I don't think they cost nearly as much as the Plastimo.
You might find a used one at a consignment shop--there's tons around here.

Thanks Benz. I'm still looking as I'm not interested in buying a $500+ Plastimo binnacle compass.

What do you think of one of these Ritchie compasses? (They are about 2 inches in diameter)




https://www.ebay.com.au/itm/19263227...3ABFBMysaqm4Vk


If I installed one of those on the bulkhead (at the front of the cockpit) what might I install on top of the steering pedestal? Maybe my Navman Depth sounder? (would that be illogical?)

[Johan Leopard51]

Originally Posted by Kettlewell

.. For example, when one nears an island group you will often encounter land and sea birds coming and going to and from the land, …

You need to be careful of which birds, or you may go very far away from land. There are (frigate I think and maybe albatross) birds that fly for days on end without landing and frigates can only settle on trees, pretty dumb for a sea bird. Apparently half their brain can sleep while the other half operates.

I need a brain like that!

[GordMay]

Is the Casio F-91W wristwatch, priced at about $14, the best watch for navigation?
Maybe, according to David Burch, founder of the Starpath School of Navigation, in Seattle

Video [01 : 06 : 45] ➥ https://onthedogwatch.com/podcast/41...h-david-burch/