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GPS and traditional navigation

rwthomas1

Sustaining Partner
hello All,
I put this topic here as it didn't seem to fit elsewhere..... My wife and I are currently "discussing" the relative merits of GPS vs traditional navigation. This occurs as our chartplotter is not working correctly and I would simply like to replace it or remove it. I don't trust it. I think a handheld would be a better stopgap solution at this point.

She eschews GPS and almost anything electronic for traditional navigation with chart, compass, parallel rules, etc. She is far more competant than I am at finding here way around using just a map, etc. Ironically she is a digital cartographer/GIS professional for income. Her claim is that once you see how inaccurate some of the data is that is used for GPS input, etc. you wouldn't be so reliant on electronics.

I am sorta clueless when it comes to traditional navigation, relying mainly on visually locating landmarks and simply knowing the water I am sailing in. Naturally this means I don't stray really far from home either... I like GPS/chartplotters as it confirms for me, or at least causes me to reexamine where I think I am, in a very simple format visually the way I like it.

My arguement is that a GPS/chartplotter, while not always completely reliable and accurate, is mostly good enough especially once it gets nasty and simply tending to the boat becomes priority. Having the electronics on the pod right there in front of the wheel makes things easier. Running below and consulting a chart is not always an option.

She will concede that point but insists that paper charts, plotting courses, etc. is still the best way. My arguement is try doing that singlehanded underway in the nasties. The electronics will seem like your friends then.

Your thoughts on these ideas would be appreciated. Just trying to stir up some constructive conversation on the relative merits of both ways. RT
 

Rob Hessenius

Inactive Member
RW- Just use the f-ing GPS. If she eschews, say "God bless you". Im not saying to abandon the paper charts. Just have a trust in technolgy. Rob Hessenius
 

CaptnNero

Accelerant
Multiple sources

I use the GPS as just one point of information, and the chart as another. Use the depth sounder, radar, your sight and that of the crew, your local knowledge, the local knowledge as shown by other boats, the pit of your stomach. the hairs on the back of your neck, and your sixth sense. It sounds like you are already doing that by relying mostly on what you see.

As for GPS strictly vs. charts, we had a local copier duplicate the six chart pages around our marina and emboss them in plastic. Then we keep the relevant ones handy in the cockpit.

There are known areas where the datum are wrong. For example, when passing thru Knapps Narrows in the Chesapeake, the GPS will consistently show you are ashore on the North side of the channel. Sometimes the accuracy can open up. I've seen it go from 15 feet to 100 for brief periods. As I understand it, the GPS and charts use the same datum. Just past the end of our pier the charts and GPS show a spit of land about a hundred feet long. I know it hasn't been there for at least ten years.

Heads up !
 
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jkm

Member III
I rely on GPS for flying, as well as sailing.

The technology, though still emerging, is essentially flawless. Equipment does have issues.

Charts are important as they tend to show obstructions (power lines, peaks etc) better to my old eyes, but younger pilots rely on GPS technology. Frankly I like the technology and find it instantaneously gratifying to know where I am.

I have never gotten into trouble while using GPS, can't say the same for charts.

John
 

Seth

Sustaining Partner
NAV stuff

Like jkm, I am also a pilot and offshore navigator. I have crossed oceans using celestial navigation only, and am old enough to have used Loran A, Loran C, Omega, Satnav, and now GPS (don't forget those awful RDF units!)

On a passage, I do maintain a DR plot, and will use triangulation from landmarks on a chart (if I am 100% sure of what I looking at), and even with radio signals.

I could even be considerd an "old school" navigator, and enjoy the tradional elements of the discipline.

BUT....while it is foolish to eschew completely real charts and plotting your position, it is even more foolish to suggest that GPS or Loran C (most of the time) are less accurate and reliable than old school navigation. It is simply not possible to take a bearing, plot the LOP on a chart, and expect this will be more accurate than a GPS fix (with VERY few exceptions). These exceptions are a good reason to have the backup method, but if the GPS signal is good, so is your position.

Some of the older units DO have errors when converting to a plotter, and the early Loran C units (sometimes often) had errors converting from TD's to Lat/Lon. I usually relied on the TD's to plot myself on a chart when using Loran.

But GPS (especially differential GPS) is used to navigate aircraft (in 3D!) at a level of precision FAR beyond what a boat would need, and this is not really something to dispute.

The best compromise is to take the raw position data and plot it yourself on a chart (if you need one), but MOST modern units will give a position more precise that anything you can transcribe onto a chart-depending on the scale of the chart, the width of a pencil line is less accurate that what the GPS is telling you, since they canplace you within a few yards of your position.

A huge benefit of GPS is the "VMG to waypoint" function-this saves you from doing the geometry and trig needed to see if 5-10% degrees off of Rumb will be a net gain or net loss, and the ability to have a real time readout of current set and drift(winds aloft for you pilots!) will allow MUCH more precise course allowances for this than tying to determine the set and drift you are getting from several plots and "cranking in" a correction factor.

Sure it is more fun and challenging to "do it yourself", but this comes at a price of accuracy and potential safety-Use GPS and back it up with an alternate method...

S
 

Captron

Member III
GPS vs. Charts (longish)

IMHO,

You need redundant navigation systems. We use a GPS Plotter at the helm which is interfaced to our radar. We use a separate handheld GPS that is interfaced to a PC with MapTech's Ocean Navigator displaying charts. The two systems are separate. We do not have either GPS interfaced with the autopilot; I prefer to make manual course corrections. We also carry paper charts for the areas we will be cruising.

The radar interface has saved our bacon in the past. The radar displays the next waypoint as a target on the screen. If that target looks off relative to radar returns we can slow down and make corrections or at least double check things. One time, at night, the radar showed a waypoint that I had picked off a current paper chart, to be squarely on land. The reason was that recent hurricanes had significantly rearranged the sand from what the chart showed. Having the radar interface as a redundant system gave us a chance to adjust our thinking before we ran aground. Likewise we don't blindly follow the GPS; we get our eyes out of the cockpit and look around.

In our system, paper charts are used for route planning and if we're out of sight of land, we maintain a plot (on paper) of our last known position every hour or so just so we could pick up a DR plot should the electronics fail.

We also rely on our own waypoints where we've been to an area before rather than pick them off a chart or rely on a cruising guide. If we have never been there before, we'll use the most reliable waypoints we can find from a trusted cruising guide; picking them off a chart is the last thing I will do. We make extensive use of the 'track' features of our GPS and Maptech especially where we need precise navigation of a pass or shallow area that we've traveled before. Memory in our GPS is a serious issue for us (only 250 waypoints, 20 routes and only 1000 or two track points). Memory in our Maptech System on the PC is not an issue. When I plan a route on the PC, I manually enter the waypoints into our 'steering GPS' just to perform one more check as a defense against the old fat finger. Electronically moving the data would just replicate a mistake. Of course, the extra keying could introduce an error but it's unlikely that both systems would have the same error.

Charts of most of the east coast (Norfolk to Miami) Gulf Coast and Bahamas (where we sail) are old. That is, the last marine surveys were conducted sometime in the last century (and in some areas the 19th century). Sure some navaid updates have been done, place name updates, obstructions in some cases but the land masses have not been updated and the depths are unreliable at least in shallow areas. Some major shipping areas get updated from recent satellite images but most areas haven't been done in a while. The computer and electronic charts we have, are identical to the paper charts and were based on them.

I hear complaints from cruisers that Maptech's charts of the Bahamas are off in places but the same sailor will then tell me he (or she) relies on the Explorer Chart Books ... Maptech and Explorer are identical... Maptech's data came from Explorer Charts in the Bahamas. Likewise the coastal US charts ... they're all based on US Government data and no different from the currently available paper charts. Where we've found the charts to be off, both the paper and electronic versions were off.

One more idea. In the Turks and Caicos Islands, we didn't have paper charts so we printed color copies off the PC charts just to have quick reference copies in the cockpit for the shallow passages along our route. Saves ducking below to look at the PC when you just need a quick look.

I recommend that sailors use multiple references and navigation systems including GPS, paper charts, radar, visual sightings, depth sounder, hand bearings, dead reckoning, identification of navaids plus a good measure of experience. If you have Loran, use it. If you're crossing an ocean, learn to use a sextant and plot regular LOP reductions. Just have multiple, redundant systems and use them all. I would never toss out the paper charts but on the other hand, I don't rely on a lead-line either. :egrin:

Capt Ron
E38 Kismet
 
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Shadowfax

Member III
I go along with what has already been said. I have a newer GPS chartplotter and I use it all the time. Here in the Chesapeake, which has to be the best marked piece of water on earth, I can constantly check reality with what the chartplotter considers to be reality and though on occasion they differ slightly, and by that I mean by maybe 10 feet, I think it does better than I could with paper charts, with compass error, drift etc..
I’m running a Garmin plotter and the charts on display are, as far as I can tell, the same as the paper charts. I still carry and use paper charts and I believe everyone should and know how to use them against the unhappy day when the GPS quits while in use. I’ve used RDF, loran, hand held GPS and without a doubt the chartplotter is the best aid to navigation since the compass or sextant.

Anyhow, that’s my two cents.
 
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windjunkee

Member III
I totally agree with his wife. Those GPS satellites -- you never REALLY know where they are. I much prefer navigating by swell pattern and star position while trailing a piece of wood tied to a string off the transom.

Pah leeeeese. I agree with redundant systems and in case of a total electical system failure and the loss of all double A batteries overboard, having a sextant and knowing how to use it is a good idea for ocean passages.

But if she eschews the electronics, does she swing the horizon with her sextant? or does she take the gps coordinates and plot them on a chart? If you're going to go totally primitive, be consistent at least.

By the way, in 1987, with a "SatNav" (rudimentary predecessor to GPS), we navigated through the Tuamotus at night with light winds and no engine (bent prop shaft). At one point, our "SatNav" fix had us about 10 miles from a partially submerged reef we were concerned about avoiding. We flipped on the radar and picked up the wave action on the reef -- and our 'SatNav' was dead nuts on. It was a beautiful thing.

Jim McCone
Voice of Reason, E-32-2 hull #134
 

CaptnNero

Accelerant
turquoise is bad

I read an article a few years ago (CW or Sail?) about a family several miles from a tropical harbor in the middle of the day. Suddenly the Captain on watch noticed he was surrounded by uncharted turquoise water way offshore at cruising speed! He tossed his book down and scrambled to start the engine. With all eyes calling out coralheads, he was able to bump his large sailboat thru the coralheads without getting stuck and pounding with the surf in there.

When they reached the harbor hours later, they surveyed and found only cosmetic damage. He told the harbormaster and he said, "yeah mon, that shoal popped up offshore last year when the local volcano erupted".

Take in all the info and expect the unexpected on watch. I've heard that the South American charts were never as accurate as we're used to here in the States anyway.
 

Mikebat

Member III
Chartplotters do not seem like a good deal to me. The charts are expensive and proprietary. If you buy a brand you later decide is not what you want, you may be stuck with it because of your chart investment. The electronics in a chartplotter are nothing special. There are only a handful of GPS chips made, and even fewer plants that produce them. Your $4000 chartplotter likely has the same chip as the $300 handheld. The markup is all in the packaging. In fact, most of the GPS receivers that come with chartplotters have the chip in the "antenna". All the chartplotter does is interpret a NMEA or similar kind of signal comingout of it. With a little PC knowledge you can get a low-power PC or notebook running Windows or Linux, or even a Mac mini, to do everything a chartplotter does, and also play movies and music, log on to the internet, etc. etc. I am adapting a Mac Mini for my boat, which will run MacENC software (can overlay ENC vector charts on top of raster charts - very nice feature, best of both worlds!). I haven't acquired the 12V-18V DC power supply car modders use to run the Mini, but even on a inverter, it uses much less than an amp. The GPS signal is provided by a handheld Magellan mounted in the cabin. NMEA allows me to see the data on my TackTick instrument displays. Bluetooth lets me do it wirelessly. I can use the handheld for land excursions, too. It's cheap and easy to replace. I bet even at a remote Mexico anchorage, somebody's got a spare handheld GPS with NMEA on the RS232 port (I have two spares, since they're cheap). That's all I need.

So yeah, I am high on high tech, but not on dedicated chartplotters and proprietary electronic charts.
 
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Shadowfax

Member III
I have a Garmin 172 C chartplotter. Color screen with every chart of the Delaware and Cheseapke Bay on it at about $500. Ths unit does everything that any other chartplotter does including interfacing with everything you might want to add. If you bought all the charts alone I bet you'd spend $1,000.00. GPS is not the silver bullet of navigation, but bang for the buck for the average user, it ain't far off
 

therapidone

Member III
Gps, Gps, Gps!

I use a hand-held Garmin GPSMAP 76 and the Blue Chart software to help guide me on the Chesapeake Bay in bad visibility and, especially, when sailing at night. In fact, even though the charts were in the cabin below, I used only the GPS with waypoints established along the race route for the 3 times I've raced in the overnight Annapolis to Solomons race. Now, when it comes to entering an an area (creek, cove, the Rhode River, etc.) for the purposes of gunkholing and anchoring, I use a book called something like "Guide to Chesapeake Bay Cruising" to get a discussion of landmarks & what to be on the lookout for in combination with my GPS.

I've thought about getting a 2nd hand-held GPS for backup on a possible DelMarVa circumnavigation, but I wouldn't want to be without charts to augment my navigation.

Regards,

Ed:egrin:
 

knewthomas

Junior Member
Let's clarify things...

I do believe my DH has misrepresented the situation. Let me clarify because there is a serious issue at hand.
1. I work with a wide variety of GPS everyday--everything from centimeter accuracy to recreational grade data. I do not "eschew GPS and almost anything electronic," in fact I have extensive knowledge of it. Much more so than most people and definately more than my DH.
2. My issue is with chartplotters, not GPS. Since I make digital maps (in essence the raster & vector data just like that on chartplotters) I do not like the idea spending a lot of money on a unit that only allows me to view someone else's data. In addition, it is the chartplotting component that is the least reliable of all navigational tools. (Funny how this is also the component that is glitchy on our unit. The GPS antenna works just fine). Therefore I have no interest in replacing our glitchy Raymarine chartplotter. DH's problem is that he doesn't want to take the lat long from the GPS and refer to the paper chart to locate himself. He wants only to look up and trust the chartplotter for his location. IMO even with a fully functional chartplotter one should always have the paper chart at hand and refer to it regularly. And regardless of having a working chartplotter, DH and anyone else who takes the helm should be able to navigate by paper chart. Now for the real question...
What navigation software are people using? I can use my professional GIS software, but perhaps there are simpler yet still functional packages out there.
 

CaptnNero

Accelerant
The rest of the story

KT, good to hear from you on this.

This glitchiness is something that I was not aware of explicity, but being a software developer it is not at all surprising ;)

Anyway, would you be so kind as to give a little more detail on said glitchiness ? You seem to be saying that the GPS tends to be accurate but the chartplotter paints you in the wrong spot. Recently I've noticed a couple of times when passing a few local markers our Garmin 172C shows us either 100 feet behind or ahead of the plotted position. Normally the plot would show us within the 15 foot accuracy that it claims in the accuracy field and validated by visual proximatey to navgation aids.

I'm hoping that the display of the lat/lon position is less glitchy than the actual plot, in which case I can still rely on mapping those coordinates periodically onto a chart as I used to with my original primitive handheld GPS unit. Perhaps that is just wishful thinking on my part.

knewthomas said:
...In addition, it is the chartplotting component that is the least reliable of all navigational tools. (Funny how this is also the component that is glitchy on our unit. The GPS antenna works just fine). Therefore I have no interest in replacing our glitchy Raymarine chartplotter....
 

footrope

Contributing Partner
Blogs Author
Pilot error

Pilotage, or visual navigation, is such a fine and useful art that it is taught in all the best sailing/boating navigation courses, both practical and in the classroom. It is not without its challenges, as any new pilot (airplane variety) or experienced boater will probably attest. Unless fog prevents it, I feel that we all should be using our eyes first. Learn to use the hand bearing compass, too. If you're not totally lost, or using the wrong chart, taking bearings will even work at night.

You can be in the middle of places where visual navigation is much less accurate than the GPS/chartplotter combination, though. I would mention Long Island Sound, the Straits of Juan de Fuca, Georgia Strait, Lake Michigan. I'm sure it's a long list. In those situations even 500 feet of position error, as displayed on the chartplotter, isn't of much consequence. And that's where the chartplotter really shines - when you want to know are you 3/4 or half-way across? Or, when staring at an approaching freighter that's doing 22 knots, "Am I in the commercial traffic lane?" Another good time to take a quick look at the chartplotter.

I would hasten to add that I've been in spots where I was within a mile in all directions of all sorts of land (islands) and couldn't be sure which way to go without serious double-checking of the compass and chart. I would also confess that I have a tendency to play with the chartplotter rather than do all that hand plotting on my paper charts. :dunce:

Radar (when available) and depth soundings are also really useful double-checks to a chart or chartplotter when you absolutely, positively, have to poke your nose into the fog or darkness.

Great thread. Thanks, KT, stating your case so eloquently. The fallibility of all our navigation senses and tools demands that we navigators, pilots, & skippers understand their limitations.

I relinquish the soapbox.
Craig

P.S. DH?? :confused:
P.S.S. attest? eloquently?
 

CaptnNero

Accelerant
R.A.M. vessel avoidance

Well said Craig. The swerves in the North-South shipping channel of the Chesapeake Bay make it tricky to visually judge the collision hazard situation with a freighter or tow barge approaching which will have to turn somewhat before reaching your projected position. What appears to be a safe crossing situation can change in a minute as one of those big fellas turns on it's way to or from Baltimore.

I also like to confirm whether the commercial traffic is in the commercial traffic lane. The GPS definitely helps to plot a position and correlate that to what I am actually seeing. Some of the large barges often are not in the channel and may have a local destination far out of the North-South shipping channel.

footrope said:
... And that's where the chartplotter really shines - when you want to know are you 3/4 or half-way across? Or, when staring at an approaching freighter that's doing 22 knots, "Am I in the commercial traffic lane?" Another good time to take a quick look at the chartplotter.
...
 

rwthomas1

Sustaining Partner
UhOh! Thats my wife talking people, she found the Ericson board.... Craig, "DH" would be me, as in "dear husband" or possibly "damned husband" etc. I'm sure she will clarify the GPS to chartplotter discrepancies and why they exist.

Regarding our own chartplotter the charting function no longer "functions" at all. The GPS part is still receiving and showing GPS time, Latitude and Longitude. My arguement is that once a piece of electronic gear is compromised you no longer trust it and it should be removed from the boat. Since she would prefer to not purchase a chartplotter instead to save money for a winter cover or a new sail, a compromise is a handheld. A handheld should be purchased as a stopgap until the unit is replaced and then the handheld serves as a nice backup.

Right now my lovely wife will be looking the chart and ask me for coordinates so she can figure out where we are. This works at the mooring. Out on the bay in 25kts heeled over when I am trying to keep the boat on course, trim sails, watch for traffic, etc. results in me having to shout coordinates at her, having to repeat them at least once, generally pulling me away from things I need to be doing. A handheld would allow her to do the navigation while I could concentrate on the boat. Is this a huge deal? Not really as long as we stay in the bay. I don't think I am going outside the bay without a handheld GPS.

RT
 
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therapidone

Member III
Oh...THAT'S what DH stands for!

And here I thought it was for "designated hitter" because you were doing all the talking for her in setting forth her position on the matter at hand.

Now, for a couple of questions that are meant to be taken good-naturedly but raise questions about the respective duties of KT & "DH". While you are at the helm in 25kt winds, why is you first-mate down below? Why are you the one worried about sail trim, traffic, etc. Shouldn't the first-mate be up there assisting and off-loading some of these duties? I mean just how much navigation calculation is necessary...we are talking (I'm assuming) the Narragansett Bay here, aren't we?

I only ask these questions in an attempt to continue airing this discussion of differing opinions held by spouses in the public space of the EYO:devil:

Now "touch 'em up" and come out fighting at the bell! :argue:

Regards,

Ed:egrin:
 

knewthomas

Junior Member
belts and suspenders

Okay, I'm not down below while sailing, I'm in the cockpit or on deck pulling lines too. Our old Raymarine is not legible in the sunlight unless one is standing directly above it. Therefore it is not usually possible for me to read the coordinates while "DH" aka RT is at the helm (he's kinda big). Since my job aboard is navigator (RT's too busy constantly adjusting everything regardless of wind speed), it is my responsibility to ensure that DH doesn't run us into the submerged boiler or up onto Calf Pasture Point, the two most common obstacles for us in Narragansett Bay. These two hazards are each marked with a single bouy but the hazard extends well away from that mark. I like to check my visual navigation (ie judgement of distance from said hazards) against the chart to ensure I won't be responsible for the call to Sea Tow. Plus it's good to practise on the bright sunny day so when the fog rolls in, I am confident in my abilities. Rob is a belt and suspenders kind of guy when it comes to mechanical and maintanence and I'm a belt and suspenders kind of gal when it comes to knowing where I am in the world. :egrin:
In regards to chartplotters, even when ours was working, the paper chart is next to me at the helm. Normally in the bay the chartplotter is zoomed relatively close in. If I want to see where I am in relation to a water tower a few miles away I can glance at the paper chart and find out a whole lot faster than I can zoom the chartplotter out. I enjoy looking at these things and following along on the paper chart. Some have critisized this as too obessive, but again, it all is honning my skill and confidence in myself for the bad day out there when the weather goes to hell and the electronics crap out and "WE" have to rely on 'my' navigational skills alone. ;)
Now about the glitchy chartplotter. Ours won't read the c-map cards anymore. When we try to access the chart info from the cards the whole unit crashes and reboots. That's unique to our unit. What is common to all chartplotters is the proprietary vector and raster data that is used as the basemap. This is only as accurate as the QA/QC protocol used by the chart manufacturer. Most companies will not discuss said protocols and it is too technical for 99% of users anyhow. BUT if your road data neatly overlays your chart data, than most likely someone has modified one to fit the other. That introduces inaccuracies. Now a recreational GPS unit is marketed to boaters and land users alike. My concern is that the chart data was not compromised to fit the road data. But I have no way of knowing this with most systems.
For me as a mapmaker, using a chartplotter is like a diesel mechanic handing over the keys to his boat to a salesman and trusting the salesman to have someone qualified rebuild the engine. When the owner is out at sea and the engine doesn't sound right, the owner (also a diesel mechanic) is now not able to access his own engine because the repair company has neatly boxed it up. I don't think a mechanic would allow this on his boat. Why would a mapmaker allow the equivalent on hers?
 
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CaptnNero

Accelerant
I think I get it

KT, thanks for the details on the chartplotter issues. It is fascinating. Maybe that road data vs. chart data stuff explains why my Garmin 172C always tracks our 5 foot draft vessel across the land whenever we transit Knapps Narrows at Tilghman Island. I should take the Garmin with me in the car across the Knapps Narrows drawbridge and see if it puts us in the water :devil:

Now please don't tell me there's a GPS system engineer out there who could tell us of the soft spots in the GPS system like KT just did for chartplotters.

I think the forum should all chip in and get KT a sextant for Christmas ;)
 
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