GPS jamming in Flordia

[Hardhead]

I agree - but then again, there were a lot of shipwrecks back in the pre-electronic navigation days too. Actually having a relevant paper chart onboard is probably THE most important safeguard to take now-a-days, IMO.

[wayne.b]

Originally Posted by Chotu

GPS is permanently jammed near the UN in the east River and has been for decades.

===


Yes, we've seen that several times. Are there any Notices to Mariners on that?

[jimbunyard]

Originally Posted by Hardhead

I agree - but then again, there were a lot of shipwrecks back in the pre-electronic navigation days too. Actually having a relevant paper chart onboard is probably THE most important safeguard to take now-a-days, IMO.

You mean besides the ability to place yourself on and read it?

[valhalla360]

Originally Posted by Hardhead

I think that's a solid idea. We've all become so reliant on GPS - for a lot of people there's no real plan B for offshore navigation. Given how easy it appears to be to jam and goof with GPS signals - it might be something ner'dowells can be doing more easily in the future.

This falls into the same category as people who "claim" they won't fly on twin engine jets transatlantic because you need 4 engines to be safe...even though modern twin engine jets are proven safe (at least when your own country isn't shooting missiles at them but 4 engine planes aren't much better in that scenario).

GPS being jammed or simply failing would be a very rare event to start with but:
- Odds are it's short duration so unless it happens while entering a tricky reef, odds are it's back up and running before you make landfall.
- With GPS down longer term, most mariners will be taking extra precaution when approaching landfall...probably more so than in the old days. Also modern boats are more likely to have strong reliable engines compared to 75yrs ago, so situations that got boats in trouble back then are a minor nuisance today in many cases.

[Cpt Pat]

Originally Posted by valhalla360

This falls into the same category as people who "claim" they won't fly on twin engine jets transatlantic because you need 4 engines to be safe...even though modern twin engine jets are proven safe (at least when your own country isn't shooting missiles at them but 4 engine planes aren't much better in that scenario).

GPS being jammed or simply failing would be a very rare event to start with but:
- Odds are it's short duration so unless it happens while entering a tricky reef, odds are it's back up and running before you make landfall.
- With GPS down longer term, most mariners will be taking extra precaution when approaching landfall...probably more so than in the old days. Also modern boats are more likely to have strong reliable engines compared to 75yrs ago, so situations that got boats in trouble back then are a minor nuisance today in many cases.

Reliable engines? I don't have an engine. I have a sailboat (not an auxiliary sailboat).

There's an old pilot joke: "What's the difference between having only one engine and having two? With two, there's double the chance of having an engine failure." When training for a multi-engine rating, you spend most of your time flying around on just one engine because there're real hazards and pilot challenges involved in having one engine shut down. If one engine fails during take-off in a twin, the fatality rate is much higher than when the only engine fails on a single-engine airplane.

I think all you've said is true for coastal cruising. But imagine you are half way to Hawaii from California. Sailing in the trades. Without at least a sextant there is a high likelihood you will miss the islands. Yes, you can just turn around and head east, but you'll be sailing upwind the entire way back. I hope you have enough food and water (or lots of fuel for your wind-assisted motor boat) 'cause it's going to be a long journey. It's hard to say how long GPS could be out of service if someone sets their mind to denying it. It would only take a few denial-of-service satellites to accomplish that.

The biggest impact would be with the loss of timing signals that are critical to services like cell phones, trunked radio systems (emergency services), stock trades, Internet routing, and litany of automated plant processes (like food processing) that depend entirely on GPS for timing and switching, and that have cheap internal clocks that will drift out of tolerance in mere hours. Commercial shipping and aviation would be heavily impacted. VTS would certainly have to drastically reduce traffic in and out of ports, and the FAA in its infinite wisdom has been shutting down the ground-based navigation systems by attrition as their vacuum tubes fail. We've put "all our eggs in one basket." GPS. It's a single-point-of-failure. People have been warning that we need a backup and eLORAN has been proposed because of its near complete immunity to jamming. But people aren't listening. "Move along. Nothing to see here."

We have a sardonic term in aviation: "graveyard progress." It looks like that's what it's going to take. Our technology dependent society making a giant smoking hole in the ground. I don't know about anyone else, but part of the charm of sailing for me is not being entirely dependent on modern technology.

The best you can do now is have the ability to use more than one GNSS constellation. And carry a sextant.

[valhalla360]

Originally Posted by Cpt Pat

I think all you've said is true for coastal cruising. But imagine you are half way to Hawaii from California. Without at least a sextant there is a high likelihood you will miss the islands. Yes, you can just turnaround and head east, but you'll be sailing upwind the entire way back. I hope you have enough food and water 'cause it's going to be a long journey. It's hard to say how long GPS could be out of service if someone sets their mind to denying it. It would only take a few denial-of-service satellites to accomplish that.

If the GPS system goes down long term, it's a major issue...as in society is going down type issue. If they start lobbing nukes, waiting it out at sea might not be a bad thing and someone sending up satellite killer satellites is likely preparing for something nasty.

Missing Hawaii - It may not be fun but turning around is certainly an option. You don't have to go dead to windward as pretty much anywhere to the east will have land. Assuming you go into conservation mode, having enough food and water is unlikely to be a major consideration.

Or simply resort to the old latitude approach. Before accurate sea clocks, they simply sailed to the latitude of the destination and then went east or west till they got there...not as efficient but in an emergency it will get you there. It's pretty easy to estimate latitude without knowing much about celestial navigation.

In order to turn this into a death sentence, you really need a lot of things to go wrong if you aren't stupid about things.

[valhalla360]

Originally Posted by Cpt Pat

Reliable engines? I don't have an engine. I have a sailboat (not an auxiliary sailboat).

Engine-less boats doing ocean crossings are about as common as all the engines failing on a jet.

If you choose to be a glutton for punishment, that's your choice and you get to deal with the issues that come with it.

[Cpt Pat]

Originally Posted by valhalla360

Or simply resort to the old latitude approach. Before accurate sea clocks, they simply sailed to the latitude of the destination and then went east or west till they got there...not as efficient but in an emergency it will get you there. It's pretty easy to estimate latitude without knowing much about celestial navigation.

I believe you may be able to teach me something here: how do you determine your latitude to within enough accuracy to not miss Hawaii (about 1 degree) without using a sextant (or an equivalent angle measuring device)?

I know it can be done to very crude and insufficient accuracy with a really good clock, timing sunrise/sunset, and referring to the nautical almanac; but if I have all that, why not bring along a sextant to determine both latitude and longitude much more precisely?

[slug]

Use a Kamal

https://en.wikipedia.org/wiki/Kamal_(navigation)

Or a shadow stick

[Chotu]

Originally Posted by wayne.b

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Yes, we've seen that several times. Are there any Notices to Mariners on that?

I've never seen it in Notices to Mariners. But it's been going on for decades. I remember when GPS was kind of new I was surprised by it and thought it was just my GPS unit going out at an inopportune time.

However, without fail, every time I pass by the UN in the east River, position data is lost. I just take it for granted now.

[redneckrob]

Originally Posted by Chotu

I've never seen it in Notices to Mariners. But it's been going on for decades. I remember when GPS was kind of new I was surprised by it and thought it was just my GPS unit going out at an inopportune time.

However, without fail, every time I pass by the UN in the east River, position data is lost. I just take it for granted now.

In all seriousness, a video of the satellite data page of your GPS when this is happening would be worth a thousand words. And an independent GPS not hooked up to your boats electrical system would be a good way to determine if it's a harmonics issue with your unit or actual "jamming", which again is just senseless as to why or how.

[Breaking Waves]

Originally Posted by Cpt Pat

I believe you may be able to teach me something here: how do you determine your latitude to within enough accuracy to not miss Hawaii (about 1 degree) without using a sextant (or an equivalent angle measuring device)?

I know it can be done to very crude and insufficient accuracy with a really good clock, timing sunrise/sunset, and referring to the nautical almanac; but if I have all that, why not bring along a sextant to determine both latitude and longitude much more precisely?

http://www.deaddropthis.com/survival...n%20(2008).pdf

Check out chapter 11 and 12 - it's actually quite amazing what you can do without a proper sextant. You do need to know some stuff.

Hawaii is a bit far north for Polaris to be super accurate with crude tools, but it would still get you there.

And there are the old Polynesian methods which are a somewhat different paradigm but do also work if you know stuff.

although once you are at all close for Hawaii . . . you can actually just follow the jet contrails.

[Zanshin]

Originally Posted by Chotu

Try it with your boat.

When I sailed by the UN while on the way from Newport to Annapolis I was close to shore by their complex and GPS worked just. Perhaps I was just lucky.

[Cpt Pat]

Originally Posted by slug

Use a Kamal

https://en.wikipedia.org/wiki/Kamal_(navigation)

Or a shadow stick

So you're using a sextant substitute that acts like an inaccurate sextant. I fail to see how that's different or better than using a sextant.

Where do I find a calibrated stick?

And how do I make any of that work without the tables in the almanac? My spherical trigonometry is a little rusty.

[Cpt Pat]

Originally Posted by Breaking Waves

http://www.deaddropthis.com/survival...n%20(2008).pdf

Check out chapter 11 and 12 - it's actually quite amazing what you can do without a proper sextant. You do need to know some stuff.

Hawaii is a bit far north for Polaris to be super accurate with crude tools, but it would still get you there.

And there are the old Polynesian methods which are a somewhat different paradigm but do also work if you know stuff.

although once you are at all close for Hawaii . . . you can actually just follow the jet contrails.

Good info. Thanks. Yes, the Polynesians were amazing wayfarers. If I had a few decades of practice and dozens of passages under the direct tutelage of experts who are now long dead, I might come close. They used all sorts of clues: wave patterns, wind, smells, sea colors, birds, cloud formations, star sights at night with the unaided eye, etc. We don't know how many were lost at sea when they got it wrong.

I've seen the converging contrails - but only on clear days when I could see to 30,000 feet. I've also seen the skyglow of cities at about 50 miles distance. The contrails only appeared to converge when I was within about 100 miles of Honolulu. I wouldn't want to follow a contrail headed to Japan. With the right set of filters, I can still take sun sights with a sextant through thin overcast that would completely obscure contrails - which prevails most of the trip.

But starting at the midway point between San Francisco and Hawaii, if my starting course was off by even 1 degree, doing the trig in my head with rules of thumb, I'd miss Hawaii by more than 100 miles without course corrections along the way.

I would expect a GPS failure - under those circumstances without a backup - to cause pure panic and despair with modern navigators.