Another Navionics Victim in Georgetown

[Jim Cate]

Be scrupulous about applying all of the basic principles of good seamanship and proper navigation -- make written passage plans,

Really? Crikeys, while I make general plans for a passage I've never once thought to write out a formal written "passage plan". I wonder if others share this breach of "good seamanship"? Seems kinda OTT for a cruising yottie.

Jim

[Palarran]

Originally Posted by Group9

From friends in insurance defense firms, the validity of the claim is often a smaller issue to the amounts of money involved and the cost of litigation. They will frequently immediately pay smaller, although somewhat questionable claims, while larger, but more justfied and valid claims will get stretched out for months, or even years, under the “starve them out” negotiating strategy that is so often utilized to get payouts reduced through settlements.

Insurance companies and firms have no consciences. Every financial decision is made with a calculator. They are not going to lose money.

Delay, Deny, Defend By Jay Feinman

It's the name of the game.

[lifeofreilly57]

I've gone through the whole electronic charting evolution and still do my planning on paper charts.
I can remember years ago sailing in dead blind fog coming into Newport, I could hear the surf breaking off of Beavertail ( a place you never want to drift into). I checked my then new Kiran unit only to be totally confused. When I plotted my position on my paper chart it was telling me I was in the parking lot of a store 17 miles north of there. Needless to say, it set my expectations for the accuracy of electronic navigation.
Needless to say, modern chartplotter are powerful, accurate tools, but like any other tool it's only as good as the individual using it.
Prudent, conservative seamanship is the most important tool. I've found that tooling around the Bahamas requires the use of every information source available, and visual reference when navigating a questionable cut. We draw 6 feet Dover tend to be conservative when choosing s cut or anchorage.
I'm a bit disturbed by the number of people who depend solely on their charting software, but it I'd a sign of the times.

[lifeofreilly57]

Originally Posted by lifeofreilly57

I've gone through the whole electronic charting evolution and still do my planning on paper charts.
I can remember years ago sailing in dead blind fog coming into Newport, I could hear the surf breaking off of Beavertail ( a place you never want to drift into). I checked my then new Kiran unit only to be totally confused. When I plotted my position on my paper chart it was telling me I was in the parking lot of a store 17 miles north of there. Needless to say, it set my expectations for the accuracy of electronic navigation.
Needless to say, modern chartplotter are powerful, accurate tools, but like any other tool it's only as good as the individual using it.
Prudent, conservative seamanship is the most important tool. I've found that tooling around the Bahamas requires the use of every information source available, and visual reference when navigating a questionable cut. We draw 6 feet Dover tend to be conservative when choosing s cut or anchorage.
I'm a bit disturbed by the number of people who depend solely on their charting software, but it I'd a sign of the times.

Loran, damn spell check. Another electronic aid.

[a64pilot]

The GPS depends solely on the Chart datum to display where you are on the chart.
While it of course helps to review your paper chart prior to and during navigation in difficult areas, as long as the datum is the same, your paper chart isn’t going to tell you anything that isn’t on the plotter.

While GPS isn’t infallible, it is the most accurate, reliable form of navigation there is. 999 times out of 1000 if the GPS tells you your somewhere you don’t think you are, your wrong.

I’ve used GPS since before it was available to the general public, initially it would only display current position and you could program a way point and get a heading and distance, but this moving map stuff was pure science fiction.
I have never, ever seen a GPS error, I’ve seen high DOP or EPE depending on brand of GPS and loss of satellite reception, but never ever seen one display position in error, not when you confirm satellite reception.

I have once over the Gulf of Mexico had my Garmin 396 simply lock up or freeze, I couldn’t even turn it off, had to remove the battery and reinsert to make it come back, and that fault never, ever reoccurred, but that was a GPS fault, that was the hardware.

DOP = dilution of precision, EPE = estimated position error

[Dockhead]

Originally Posted by Jim Cate

Really? Crikeys, while I make general plans for a passage I've never once thought to write out a formal written "passage plan". I wonder if others share this breach of "good seamanship"? Seems kinda OTT for a cruising yottie.

Jim

I ALWAYS make a written passage plan, for anything other than a short day sail in familiar waters.


My form is not very formal, but I think it's essential, especially in tidal waters, to have all the calculated and gathered data you need for the passage, in one place, in writing. Otherwise, what's the point of doing any navigation or planning? I write down:


Tidal streams
Tides at origin and destination
All the gathered weather information

List of way points

Notes from chart work -- hazards, etc.

Notes for pilotage -- clearing bearings, buoys, etc.
Sunrise/sunset
ETA
Alternative harbours
etc.


when i keep a paper log, I just used the log book for this -- the left sides were for passage plans, right rides for log.


Now I keep an electronic log, so I just use a notebook


I don't really understand how anyone can do competently a passage of any complexity, without a passage plan.


It's a legal requirement for UK flag vessels, although it is not required that it be in writing. But UK flag vessels are obligated to gather relevant information and do planning, before going to sea. It seems like very elementary seamanship to me.

[Dockhead]

Originally Posted by a64pilot

. . . While GPS isn’t infallible, it is the most accurate, reliable form of navigation there is. 999 times out of 1000 if the GPS tells you your somewhere you don’t think you are, your wrong.. . .

Every source of data should be interpreted with a view of its likely accuracy and reliability.


I think GNSS is even more reliable than you say, I guess by many orders of magnitude. Especially if you are getting not just GPS but GLONASS and Galileo. The chances of all of these being off must be vanishingly small.


I don't verify GNSS data beyond basic sense check. But charts are an entirely different matter. I try to always have at least two sources of cartographic data on board for every place I will be, and check them against each other. Then always check chart against radar image (radar overlay on the plotter is brilliant for this). Then always exercise caution in water shallow enough for there to be hazards. Always use depth alarms set appropriately, radar guard zones, etc., and always keep a good visual watch.

[conachair]

Originally Posted by a64pilot

DOP = dilution of precision, EPE = estimated position error

This is a little usb gps just resting against a window inside on a steel boat, is horizontal dilation the best indicator of accuracy?

[transmitterdan]

Originally Posted by Dockhead

Every source of data should be interpreted with a view of its likely accuracy and reliability.

I think GNSS is even more reliable than you say, I guess by many orders of magnitude. Especially if you are getting not just GPS but GLONASS and Galileo. The chances of all of these being off must be vanishingly small.

It depends on where you sail. Russia is screwing with GNSS in several locations. More recently they have expanded operations into regions that a lot of people sail. Mostly they are screwing with commercial shipping but in some cases such as coast of Turkey, Black Sea and far North Sea they affect cruisers. Iran regularly screws with GNSS in the Persian Gulf and SoH.

https://rntfnd.org/2019/03/27/exposi...-c4ads-report/

I would just turn of GLONASS if the receiver has the option. But then I know too much about what the Russians are doing to trust their system at all. Ignorance is bliss as they say. So I guess the opposite is knowledge can be terrifying.

[Dockhead]

Originally Posted by transmitterdan

It depends on where you sail. Russia is screwing with GNSS in several locations. More recently they have expanded operations into regions that a lot of people sail. Mostly they are screwing with commercial shipping but in some cases such as coast of Turkey, Black Sea and far North Sea they affect cruisers. Iran regularly screws with GNSS in the Persian Gulf and SoH.

https://rntfnd.org/2019/03/27/exposi...-c4ads-report/

I would just turn of GLONASS if the receiver has the option. But then I know too much about what the Russians are doing to trust their system at all. Ignorance is bliss as they say. So I guess the opposite is knowledge can be terrifying.

Scary stuff. But are they able to spoof all three systems at once?



And maybe you understand something about how our receivers work -- they are receiving data from all three systems all the time, right? What happens if the data conflicts?

[Pete7]

Originally Posted by Jim Cate

Really? Crikeys, while I make general plans for a passage I've never once thought to write out a formal written "passage plan". I wonder if others share this breach of "good seamanship"? Seems kinda OTT for a cruising yottie.

Jim

We do once outside the protected waters of the Solent, all be it on a reporters note pad next to the log and chart. Tide times, route and weather synopsis, Plan B if we turn back or head elsewhere.

In a previous life as a diving supervisor it was written in chinagraph on the back of the dive slate. Date, tide times, weather, route, hazards, etc along with dive details and people on board. Duties allocated to individuals for first aid, coxwain, dep supervisor in my absence etc.

I think a passage plan is one of the very few requirements of SOLAS V on small vessels (under 13.7m).

Pete

[Captain Bill]

Originally Posted by a64pilot

The GPS depends solely on the Chart datum to display where you are on the chart.
While it of course helps to review your paper chart prior to and during navigation in difficult areas, as long as the datum is the same, your paper chart isn’t going to tell you anything that isn’t on the plotter.

While GPS isn’t infallible, it is the most accurate, reliable form of navigation there is. 999 times out of 1000 if the GPS tells you your somewhere you don’t think you are, your wrong.

I’ve used GPS since before it was available to the general public, initially it would only display current position and you could program a way point and get a heading and distance, but this moving map stuff was pure science fiction.
I have never, ever seen a GPS error, I’ve seen high DOP or EPE depending on brand of GPS and loss of satellite reception, but never ever seen one display position in error, not when you confirm satellite reception.

I have once over the Gulf of Mexico had my Garmin 396 simply lock up or freeze, I couldn’t even turn it off, had to remove the battery and reinsert to make it come back, and that fault never, ever reoccurred, but that was a GPS fault, that was the hardware.

DOP = dilution of precision, EPE = estimated position error

I've only seen a significant GPS error once and that was tied to a dock in Whortonville, NC. I was getting ready to go out and had the chartplotter on and suddenly I was 14 miles away in the Bay river. I heard a jet flying over and looked up and saw an EA6B heading for Cherry Point. When he went over the horizon I was suddenly back at my dock.

[Pelagic]

My "passage plan" is my log book, although like Jim......

I never think of it as a "passage plan" .....
...... just a "passage record" with salient notes of precautions taken due to wind, tides, paper charts used.

To me, a passage plan is what you tell Customs, port authorities., Coast Guard and family

[bcn]

As GPS signals are very weak, almost as low as a background noise, interference - by chance or at will - is quite simple.
Jamming is possible but not frequent. At least when sailing...

Spoofing or injecting wrong data is quite simple on local base, being close to the GPS receiver.
When a "three letter agency" reports that they had observed something like this on a regional extend and are indicating that the "bad ones" have done it you can bet that
a) they do it themselves and
b) they are asking for budget to do in a bigger scale

DOP is not an indicator of actual precision. It describes the quality of the geometry of satellites in view, hence a condition for reception, but no guarantee.

Inertial measurement systems with GPS support will give an estimate of error.
RMS for GPS with WAAS/EGNOS is in the range of 2m. Or better with server grade receivers.

There are quality reports available for GPS or Galileo for example with all the statistics one might want to see.
An error of 30m should be an intermittent or spontaneous one, not a systematic one. Or bin your receiver/antenna/cables...

We are getting away from the Bahamas and Navionics here, I fear...

[bcn]

Originally Posted by conachair

This is a little usb gps just resting against a window inside on a steel boat, is horizontal dilation the best indicator of accuracy?

The GPS error in Z, altitude is usually about twice the error in X/Y position.
The "jitter" of 50cm observed here looks sound.
However a question would be for the manufacturer of the GPS chip what he reports on which base regarding the error.