Thank Gd for GPS

[Ziggy]

Originally Posted by Mike OReilly

GPS is great. I love it, but I would never trust it as my sole means of navigation in tight, unknown waters. In parts of my home waters (north shore Lake Superior) the charts can be off by up to 1/4 nm or more (base on our GPS fix). When the fog rolls in, as it often does, you better have a plan B that doesn't rely on GPS.

The problem seems not so much with GPS, per say, but with the charts that you translate your GPS fix on to (be it electronic or paper). I assume it's b/c the charts are based on rather old surveys (40+ years in some cases up here). This kind or error would be far less obvious before electronic navigation, but with the advent of very accurate fixes (i.e. GPS), I bet there are many old charts that show similar errors.

I know most rich urbanized areas have very accurate charts, but I wonder about less wealthy parts of the world. And by that I mean most parts of the world. Do they also suffer from inaccurate charts? If so, relying on GPS to navigate in close quarters would seem to be folly.

Are you sure you had your GPS set to the correct datum? Some of the older charts of the Great Lakes are referenced to the North American Datum of 1927 (NAD 27), rather than the currently standard WGS 84. In some places on Lake Superior the difference between the two coordinate systems can be close to 1/4 mile. I'm not sure about the Canadian charts, but at least the U.S. charts based on the government surveys as old as 1920s are usually very accurate.

[John A]

Originally Posted by delmarrey

Au contraire! But no thanks!

I believe that GPS has turned the waterways into a freeway where any jack with enough money can just shoot out do his thing and shoot back half blind.

What ever happened to good ole seamanship? As a new sailor back in the 70's it was a challenge just to sail from San Diego to Catalina Is. It took the bravery knowing that if you don't make it you could be lost at sea, which kept the useless land bound. Now a daze people head off shore looking at the GPS with little to no training or concern. They rely on the GPS as if it were another hand. And with the DSC we now have to rescue these jerks. There needs to be a weather fax attached as well.

If the satellites ever drop out (war time/solar flares) the people depending on these devices will cease to travel out of the sight of land, which could be a good thing IMHO. The waterways are way over populated these days with untrained ID10T's and now even the women are braving the roads where they didn't before.

Sure, I like GPS too, but only b/c is it lazy, and with getting old, lazy is nice. It's a fun toy that has allowed me to slack off on my nav skills and take chances where I would have not before. Which has also ruined the nice secluded places I once enjoyed with others of the same skills/interests.

It would be nice if I were 20-30 years older so I wouldn't have had to endure the ignorance/selfishness of this modern society and it's complicated toys.

Yours Truely,
Thee Old Fuddy Duddy

This reminds me of my grandfather who decried the introduction of the automobile as the ruination of society.

[Rakuflames]

Originally Posted by Ziggy

Are you sure you had your GPS set to the correct datum? Some of the older charts of the Great Lakes are referenced to the North American Datum of 1927 (NAD 27), rather than the currently standard WGS 84. In some places on Lake Superior the difference between the two coordinate systems can be close to 1/4 mile. I'm not sure about the Canadian charts, but at least the U.S. charts based on the government surveys as old as 1920s are usually very accurate.

That kind of situation is unlikely where I am, but what is Plan B in the fog?

Where I am, in the channels I typically navigate, my chart plotter is reliable enough that I can be sure I'll stay beween the red and the green and in the channel. Short of anchoring and then being an obstacle for any other boat stuck in the fog without radar, what's the plan B?

[delmarrey]

Originally Posted by John A

This reminds me of my grandfather who decried the introduction of the automobile as the ruination of society.

So, who's complaining about the pollution? The sacrifice of a clean/quiet environment does not justify modernization.

[Mike OReilly]

Originally Posted by Ziggy

Are you sure you had your GPS set to the correct datum? Some of the older charts of the Great Lakes are referenced to the North American Datum of 1927 (NAD 27), rather than the currently standard WGS 84. In some places on Lake Superior the difference between the two coordinate systems can be close to 1/4 mile. I'm not sure about the Canadian charts, but at least the U.S. charts based on the government surveys as old as 1920s are usually very accurate.

Thanks Ziggy, yes we switched our datum reference. It's an excellent point though.

[delmarrey]

Originally Posted by Rakuflames

That kind of situation is unlikely where I am, but what is Plan B in the fog?

Where I am, in the channels I typically navigate, my chart plotter is reliable enough that I can be sure I'll stay beween the red and the green and in the channel. Short of anchoring and then being an obstacle for any other boat stuck in the fog without radar, what's the plan B?

That's what bells, horns and lights were for. So, are you saying you wouldn't be out there w/o a GPS?

[Rakuflames]

Originally Posted by delmarrey

That's what bells, horns and lights were for. So, are you saying you wouldn't be out there w/o a GPS?

Please show me where I said that. However, lights, bells and horns won't let you see the channel, and where I am, in lots of places there are very big bumps on the bottom of the ocean floor.

Using lights, bells and horns still depends on the other boats to hear/see you in time, and could well mean a sleepless night.

If I were near a channel I would want to get in if I were enveloped in thick fog. My chartplotter would be a tremendous aid in these waters. And yes, I have a backup.

I fell into this trap yesterday, talking about the circumstances where I sail as if it were everyone's circumstances.

If I sailed in San Fransisco Bay, I might have more strategies for fog than for groundings, but I live at ground zero for groundings. But I've never been in fog so bad I couldn't see where I was going here. It can happen, but it's rare, and even rarer for it to last.

[bobconnie]

A few of us olde's remember when you used your ears and eyes and a chart that showed the make up of the bottom,IE- shells, sand, gravel ect thats why they HAD wax in the bottom of lead lines, its really amazing how you can find your way by depth and bottom make up ! used to have book with what I needed to remember to get over most of the North Coast Bars, and river entrances. heck 30 years ago old Loran was The big thing to get ya home and it worked but it went out to !! no matter how much electronics you have, you still need paper charts and most important HARBOR Charts for your area. just 60 yrs of sailing makes me say that LOL Im just old but im not lost !! Bob and Connie

[bobconnie]

And one more tool most of us oldys carry is a Coast Pilot for the area your cruising. Its a great navigation tool and needs no electricty !! bob and connie

[delmarrey]

Originally Posted by Rakuflames

Using lights, bells and horns still depends on the other boats to hear/see you in time, and could well mean a sleepless night.

Assumption of risk!
Not sure a GPS would help you there either. Seamanship is not for the faint hearted. It does require endurance and to persevere in all circumstances. Otherwise your lost.

[AussieGeoff]

Bear in mind that plain vanilla GPS has a CEP of around 30ft, no manual celestial navigation process will be that accurate, but if the battery craps out or the unit itself dies, you better have a backup or you are just plain lost.

Differential GPS is much more accurate, depending on your distance from the DGPS reference station, it can be sub metre. Surveyors use specialised DGPS systems that have accuracies measured in centimetres or less. The technology is good, but you have to understand both it's level of accuracy, it's limitations and be very aware that the geoid model it uses is not perfect. Neither are maps and charts and datums are a minefield for the unwary.

If you aren't careful, a GPS will wreck you with precision as easily as it can get you home. I have personally seen the classic trap of a h/h GPS position with the datum set to WGS84 (the default, though most GPS now directly support many different datums) being plotted on a map with AGD66 datum. This was on land and almost resulted in a party of cadets walking off a 30m embankment instead of down a gentle slope. A similar mistake on water could put you on a reef. Fortunately someone who was aware of such issues was along and sorted it out, much to the consternation of the cadet supposedly leading the push. It was a good learning experience though, I guarantee it's a mistake no one in that party would ever make again.

I like GPS and use it a lot, but I approach it with the understanding that you need to be sure the GPS and the chart (be it paper or electronic or scanned and calibrated) are both on the same datum and that the location of known fixes agrees with the GPS. The system itself is quite reliable now that the SA nonsense is permanently turned off for most people, but human errors and datum errors or just plain inaccuracies in charts can trap you badly.

If all else fails, radar and/or visual fixes can be manually plotted if you are in sight of land. Out in the deep blue, celestial is all there is, so if you are dependent on GPS alone (and many people don't savee celestial and never will) you need multiple redundancy from loss of equipment due to random failures. This includes something like a lightning strike that can zap just about everything aboard. A h/h GPS in bubble wrap in a sealed metal container (Faraday cage) will probably survive.


AussieGeoff

[Rakuflames]

Originally Posted by delmarrey

Assumption of risk!
Not sure a GPS would help you there either. Seamanship is not for the faint hearted. It does require endurance and to persevere in all circumstances. Otherwise your lost.

I guess you forgot the part where I said IF I WERE NEAR A CHANNEL I might just choose to go in. THAT is where the GPS would help IF the channel markers are accurate. Around here they ussually are as they're usually on pilings. Sometimes you see a floating can or nun but not often.

I think it's really easy to sneer at the newer technology and brag about not using it, but I don't have a problem with the old AND the new together. A chartplottter can give you remarkable detail but unless you've got a really big one (even then) it's not so good at the big picture.

A paper chart can give you the big picture but you can't zoom in on it to get more details.

I'm making a big distinction here between a chartplotter and a handheld GPS.

[rebel heart]

A couple of years ago on a clear night a guy couldn't find his way into San Diego harbor (which has channel markers going out ~3 miles, and A morse on the racon at the safe water marker, and a lighthouse on the point). He had to get towed in because the chart plotter wouldn't read the data card.

This kind of stuff happens because people who have no business taking others to sea feel safe doing so because of their gadgets:

California boating guide-news & classifieds

The most recent incident began at about 10 p.m. March 26 when the skipper of a 42-ft. sailboat could not find the entrance to San Diego Harbor. Conditions were clear with a high marine layer.

"He was south of the Zuniga Jetty off the Hotel del Coronado and couldn't find the channel due to lights in the background," said Sea Tow Capt. Greg Dreischmeyer.

"He had been stuck searching for the channel entrance for four or five hours and for some reason couldn't get his chart plotter to function; it kept reading data error every time he tried to load the card for the San Diego area."

The conditions were clear, but the skipper couldn't distinguish the channel lights from the background lights. Finally, at about 1 a.m., the rental boat's skipper called the Coast Guard on VHF radio Channel 16. Since the vessel was in no imminent danger, the Coast Guard contacted the private towing firm Sea Tow to lead the craft into the harbor.

[rebel heart]

*** I'm not commenting on the reasonable and normal use of GPS: it's a great tool and I use it all the time. But if you wouldn't feel comfortable navigating an area without it then (personally) I'd question your skills as a mariner. If you want to risk your own neck that's one thing but make sure you tell your passengers that you're going to stand there with your thumb up your ass if the GPS packs in because you have no idea what to do next.

[lateral]

Plotters, & GPS are a trap for the unwary if not checked up by other methods
in less travelled waters. To know exactly where you are via GPS is of little consolation if the reef you are cleaning your bottom on is not marked/ out of position. Like the Swedish couple coming into Musket at night, first time. Blind faith in silicon & man made pretty pictures. The ICW must be a nightmare of shifting obstacles.