The Modern Navigation Trap

[colemj]

Originally Posted by colemj

Our 1998 B&G GPS was a differential unit. It did not require a separate vhf receiver (other than whatever circuitry was in the GPS sensor itself), used a standard 1998 Garmin DGPS-capable sensor, and did not require any subscription fee. There was absolutely no way to track anyone using the system.

It always had a DGPS connection in the east coast US, but by Puerto Rico, there were no longer any stations in range and we have not encountered one that our receiver understands in the rest of the Caribe. I believe the US radio stations were setup and maintained by the US Coast Guard.

These units were very common before WAAS, and have been almost completely supplanted by WAAS now in the consumer marine market. DGPS still exists in the surveying and other technical markets (and is how the past America's Cup maintained 2cm accuracies). The USCG stations are still transmitting.

Mark

Oops, let me make a correction to this post. I forgot that our DGPS WAS a small separate black box receiver with a small separate antenna. The B&G took correction signals from it and did the calculations.

The rest of what I wrote is true - there was no fee and no way to track anyone.

AFAIK, DGPS for normal users is not extinct - the USCG DGPS stations are still transmitting, so anyone with a DGPS receiver in range can still use it. I don't know of any current consumer brand DGPS-capable units being sold now, however.

Mark

[Dsanduril]

Originally Posted by noelex 77

...Cruising sailors often seem quite happy with a relatively poor GPS position signal, but I think there are real practical benefits in striving for the best possible position information. At least make sure you have a good antennae signal and enable SDGPS (WAAS and EGNOS) where available. Especially EGNOS in Europe. Many boats do not have this correctly set up...

I agree wholeheartedly, but as we get more accurate it does bring up the modern trap question of "highways" between waypoints. I frequently make use of the ability of my autopilot to steer based on my GPS. This frees me from having to actually make drift and leeway calculations (modern trap lazy). On a passage I'm not usually navigating this way, but on short trips very well could be. What happens on a three-day weekend between Marina del Rey and Avalon when 50 boats all use the same waypoints, let their autopilots steer, and have the GPS minimize XTE?

There have always been my brother's wife's cousin's nanny's brother's best friend stories about this, anyone here have direct experience with boats using accurate positioning and steering by GPS resulting in collision? In the bad old days before modern navigation that trip would have resulted in about a mile of drift and people accounted for it more or less accurately, resulting in a natural spread of actual course lines. With modern navigation and computers making the course decisions there is no spread, if we all put in the same waypoints we will all end up with the same COG.

As we (I say that collectively, not referencing specific individuals) come to rely on these magic boxes, we're sure they will get us where we need to go, so don't learn the basics. The next thing that fails is watchkeeping (the boat will get us there) and then I can see this scenario becoming real.

I guess the bottom line is that it's a tool like any other, and can be put to good use or poor, depending on the skill of the user. So what do we do to instill the skill when the tool (from the outside) appears to be so darn easy to use?

[hpeer]

Last fall, A fellow coming up the Delaware River set a buoy as a way point, and found it.

The result was a pretty good size hole about 6 feet a aft the bow, starboard side. Clean through with radiating cracks out a few feet.

I talked to him and saw the boat.

Does that count?

I came damn close to whacking a lighted day mark at night, but that was my fault. The Mark 1 brain unit went dead.

[Dsanduril]

I think that counts. I've had a number of encounters at sea that only avoided collision by dodging on my part. I suspect that these were GPS track related, but never being able to even raise someone on watch on the other vessel I have no way of knowing.

For the flip side of this coin, see this story:

https://www.latitude38.com/lectronic...yid=927#Story2

I was about 100 yards behind and 50 yards to the west when this happened and stood by for a couple of hours while the Coasties came over and took everyone off. Notice the line "I had the GPS map on but hadn't zoomed in because I was looking for the entrance buoys.". Familiarity with the harbor led to not using the modern tools that were actually aboard and running, and ended in a very sad situation.

[hpeer]

I hate, no HATE, the way some packages de clutter when zoomed out. I hear that the problem changes depending upon where you are. I have had both Navionics and CMap running and much prefer CMap.

Take, for example, Middle Rock, going into Marblehead. It's maybe a couple of acres, but it falls off the display if not zoomed in sufficiently. If you are coming in at night, as I seem to always do, and are not familiar, and are trying to keep some perspective (especially on a small display) you may well not have all hazards visible, and not know it.

I also prefer raster images when possible. I like Fugawi because it will eat most any format and I have old raster charts ( Canada) and it will also do GE.

I almost hate to mention this because I don't know if I can adequately describe it.

There is a place I KNOW to be off on the charts, about 1,500 feet. The CHS charts carry warnings and I have gone in there on CMap, straight through the cliffs.

BUT, when I bring it up on Fugawi, and do a GE overlay, they match exactly. So clearly GE is wrong in this area. That kinda put me off using GE for nav.

[dacust]

Originally Posted by hpeer

I hate, no HATE, the way some packages de clutter when zoomed out. I hear that the problem changes depending upon where you are. I have had both Navionics and CMap running and much prefer CMap.

Take, for example, Middle Rock, going into Marblehead. It's maybe a couple of acres, but it falls off the display if not zoomed in sufficiently. If you are coming in at night, as I seem to always do, and are not familiar, and are trying to keep some perspective (especially on a small display) you may well not have all hazards visible, and not know it.

I also prefer raster images when possible. I like Fugawi because it will eat most any format and I have old raster charts ( Canada) and it will also do GE.

I almost hate to mention this because I don't know if I can adequately describe it.

There is a place I KNOW to be off on the charts, about 1,500 feet. The CHS charts carry warnings and I have gone in there on CMap, straight through the cliffs.

BUT, when I bring it up on Fugawi, and do a GE overlay, they match exactly. So clearly GE is wrong in this area. That kinda put me off using GE for nav.

Can you give details? I have always been suspicious about people blindly saying GE seems to always been dead on.

-dan

[Safari38LH]

I agree. We used Navionics last year in Nova Scotia and when zoomed out you miss a lot of stuff. It's particularly irritating when you are trying to identify headlands and other natural placemarks that you are looking for based on the cruising guides. The book says take a left at "Pine Hill Point", which one is that? Thank g we have paper charts!

[nigel1]

Originally Posted by Dsanduril

There have always been my brother's wife's cousin's nanny's brother's best friend stories about this, anyone here have direct experience with boats using accurate positioning and steering by GPS resulting in collision? In the bad old days before modern navigation that trip would have resulted in about a mile of drift and people accounted for it more or less accurately, resulting in a natural spread of actual course lines. With modern navigation and computers making the course decisions there is no spread, if we all put in the same waypoints we will all end up with the same COG.

The "Oil Trader", an offshore platform supply boat was on passage to a rig off West Africa, and plugged the rigs position into the GPS, and set the auto pilot to track control. The result can be seen in the attached picture.

[s/v Beth]

You guys arguing about this stuff is really funny. Seeing if you can navigate through a rock field by just using GPS or google earth or paper+plastic is all a flawed conversation. Why? Because the earth is constantly changing! And not by just a inch every thousand years like we used to believe. Japan moved by eight feet at the last earthquake! Indonesia moved by more than 10 (Sumatra). There were areas that were very deep that are now shallow! And on a more mundane note, I can tell you the sand at the entrance to Boca Grande in Florida changes every year too. You going to trust your handy navigational do-all doohickey when coming into a narrow unknown channel? If you are captain, let me step off the boat now.
I don't care what up to date picture or chart you have, its not always going to be right, and if you trust it to get you through it will fail you. It may have been accurate down to the inch when it was made, but guess what: we all live on tectonic plates. And these plates are floating in a sea of molten rock. And they move.
So not to be snarky or anything, but there will always be a place for looking out of the boat, and for nervous skippers during a thick fog. (and maybe that why it is so much fun)
Quake moved Japan by 8 feet: USGS

[Randy]

Originally Posted by Cheechako

Best comment on here. a chart or gps is just another tool. Take it with a grain of salt and .........USE YOUR EYES AND BRAIN!

And this is what's called navigating, it's not about looking at a screen and thinking that because your box says you're somewhere you HAVE TO BE BECAUSE YOUR BOX SAYS SO.

Sent from my SAMSUNG-SGH-I337 using Cruisers Sailing Forum mobile app

[hpeer]

Originally Posted by dacust

Can you give details? I have always been suspicious about people blindly saying GE seems to always been dead on.

-dan

Screen shot of chart plotter. Lets see if this is clear. Presuming it is, you can see my track through the headlands.

But, when using Fugawi 4.5 in split screen with GE, and doing an overlay, the headlands and harbor line up.
......Damn.....
Image is not attaching, says "Rotate Image"
Started to happen a couple of days ago.

Try this PhotoBucket link to the same image.

http://s23.photobucket.com/user/hpee...ml?sort=3&o=33

[goboatingnow]

Whether you use paper or digital or gps or both or whatever, all navigation methods and processes have inherent failure modes. You just have to be aware of them.

Dave

[dacust]

Originally Posted by hpeer

Screen shot of chart plotter. Lets see if this is clear. Presuming it is, you can see my track through the headlands.

But, when using Fugawi 4.5 in split screen with GE, and doing an overlay, the headlands and harbor line up.
......Damn.....
Image is not attaching, says "Rotate Image"
Started to happen a couple of days ago.

Try this PhotoBucket link to the same image.

Francois Bay Photo by hpeer | Photobucket

Yep, for me, all photos are only downloading partially, now.

But I got it off photobucket. Thanks!

So, the position says it is from "cursor position". I can't make out the cursor, or does that mean the center of the screen in this case?

Sorry for asking all the details, but before I put something on my chart errors page, I want to be able to say I know if for a fact.

Thanks, again.

-dan

[glenn.225]

Hpeer

A great deal of that part of the "Island" was last charted by the British in the 1800's. It's not much used by anyone except local fishermen and they know it by rhyme.

[hpeer]

Originally Posted by dacust

Yep, for me, all photos are only downloading partially, now.

But I got it off photobucket. Thanks!

So, the position says it is from "cursor position". I can't make out the cursor, or does that mean the center of the screen in this case?

Sorry for asking all the details, but before I put something on my chart errors page, I want to be able to say I know if for a fact.

Thanks, again.

-dan

Cursor is in bottom right, to the right of the bouy.

Also, I just went back to verify this as it has been a few years since I looked at it. And it is.

However, I have now noticed something additional. What I see now is that the area at Francouis Harbor (and also at Grey River where there is also a problem) someone/somehow did an overlay on the GE presentation. Since I new there was a problem there, that is the place I went to look. (And at Grey River.) I "assumed" that the chart overlay would be the same everywhere. It is not.

I now think that "they" (Fugawi??) have "fixed" the error by adding some "adjusted" chart info to the GE view.

They are out for a long weekend so I can't ask them until next week.