Electronic Charting vs Cruising Guides
This article generated a surprising number of responses on the old Abaco Message Board. The article is presented as it appeared, followed by a number of response posts.


Last summer we visited a friend who lives in Sarasota. He had just taken delivery of a brand new 38-foot express cruiser, complete with a state of the art 12” electronic navigation display/WAAS-GPS. He demonstrated the unit to us, bragging about its “10-foot accuracy.” We threw off the lines, and watched in fascination as a little icon on the display showed the boat’s movement against a nautical chart. As we headed out through the pass, he showed his intended deep-water route on the display.  We looked up, and to our surprise, saw that we were headed for a shoal that couldn’t have been a foot deep. We wound up making a substantial detour, finding 6’ of water in an area the chart noted as “uncovers at low tide.”

This past January an American nuclear attack submarine struck a seamount off of Guam; the sub was at 500 feet, traveling at 33 knots, in an area that was charted as “6000 feet.” A few weeks ago, someone posting on the Abaco Board noted that Spoil Bank Cay did not even appear on his newly acquired electronic charting system. If WAAS-GPS has 10-foot accuracy, and these new chart display systems can focus down to individual slips at a marina, how can these discrepancies be occurring?

Ben Ellison’s Electronics column in the April ’05 issue of Power & Motoryacht magazine featured an interview with Nigel Calder, author of How to Read a Nautical Chart. Calder points out that electronic charts are simply digitized versions of standard NOAA and DMA paper charts, many of which are based on information gathered prior to 1900; you read that correctly, 1900! Soundings were obtained by “heaving the lead,” and locations determined using surveyors techniques: triangulation of lines of position derived from observations of shoreline-based objects, again, prior to 1900.

These errors are further compounded by the fact that in this era there was no reliable mathematical model for transferring positions taken on an irregularly spherical object (earth) to a flat charting system. Our GPS machines use the WGS84 map datum, which supposedly corrects for these errors, but not all reference charts have been converted, and the resulting error can be as much as 330 yards on some NAD27 US charts, (only five years old); the error on some non-US datums can be half a mile!

Another problem is the false sense of security an operator can get by zooming down on a position. Even though you may be able to see great detail, the position of these details can easily be off on a 1/40,000 scale chart by as much as 66 yards. When you consider the implications of the above, it becomes obvious why boaters who attempt night passages using electronic navigation through narrow passes can run aground, with disastrous results. In 2003 a large sailboat slammed into Fowl Cay Reef while attempting to run North MOW pass in the pre-dawn hours. He missed by over half a mile, and we wonder if he was simply counting on his electronic chart to get him through. Depending on the chart system, the information he was using may have been based on surveys performed by the British Admiralty 200 years ago!

The electronics on our boat, Attitude Adjustment, are about 10 years old. We have a GPS/chartplotter that displays waypoints I have entered on a black screen. I have navigated through the coastal waters of East Florida, the Keys, Abaco, the Biminis, and the Berry Islands, and have had no difficulty. I make extensive use of cruising guides, particularly Dodge and Wyatt; Pavlidis is useful as well. The great advantage these sources have is this: the author will tell you “on X date I went from point A to point B, as defined by WAAS-GPS, and I encountered W, X, & Y, and found a minimum depth of Z feet at MLW.” To me, that is far more useful than a fancy electronic picture that may be based on very inaccurate information. And, at least in the case of Dodge, the information is updated annually. Thus, I can set up waypoints that define my route from, say, the mouth of Ft. Pierce Inlet to the entrance to Spanish Cay Marina, and I have the assurance that someone reliable has gone before me and verified the route.

As the price and size of these fancy gizmos comes down, they will wind up in the hands of more and more casual users, who will then unknowingly be subject to their errors, at least until our reference nautical charts are updated and corrected. I am aware that at least one company that produces charting software has incorporated some of Dodge’s information; this is certainly a step in the right direction.

I had the opportunity to visit to our local West Marine outlet today. The manager showed me two new pieces of hardware, one made by Raymarine, one made by Garmin, that are "all in one" displays. They have the ability to display a sonar image of the bottom, a nautical chart, and a radar. In addition, each device can overlay the radar image on top of the nautical chart, such that the user can directly correlate what he sees on radar with what is depicted on the chart. I think devices such as this are a step in the right direction.

However, they still do not solve the question of what the bottom ahead of you looks like, especially in poor visibility or at night. Being able to use radar to establish lines of position can certainly help the skipper navigate in poor vis. But I'm still concerned that people will be tempted to plot waypoints and routes directly from electronic charts that have significant positional errors. The guy at West Marine called up a chart on a Raymarine display, clicked on two positions, established waypoints, and made a route. But, he could not promise me that there were no obstructions on said route, just that "the chart doesn't show any."

Depending where you are on the Bank, radar will not get you out of this potential dilemma. Quite simply, if you are running on the Bank, you are taking a big chance if you have poor vis, you can't see the bottom, and you're counting on info from a fancy electronic chart. This is where the cruising guides really shine, you get the assurance that someone went before you and found the route to be free of obstructions.

In summary, even the presence of the most sophisticated electronic instrumentation does not relieve the skipper of the absolute responsibility to watch where’s he’s going, and to count on his senses to alert him to a potentially disastrous error in navigation.

Responses from the Abaco Message Board:
Pellucid
A couple of years ago, I was moored in Hopetown harbor with a crew of boy scouts. About 7AM, the BASRA boat roared across the harbor, siren blaring. I put the VHF on 72 so the boys could listen to a rescue in progress. A 40-something-foot motor cruiser had run hard up on the reef, and water was over the engines. Thanks to the quick response from BASRA and nearby vessels, they were able to get the boat dewatered and off the rocks. Once it was afloat, they asked Rudy Malone to guide the boat through the reefs at the north end of Elbow Cay so they could take it to the boatyard. Later that morning, I saw Rudy and commented on the morning's excitement. He said "That GPS will run you aground every time!" I think those are words of wisdom. Knowing where you are is no substitute for knowing what you are doing. If I had to choose only one electronic item aboard, it would be radar and not GPS. For coastal cruising, you can get "close enough" with a compass and time elapsed. Radar will show you the shoreline contour, breakers, nav aids, squalls, and other vessels. All in real time, with measurable range and bearing, not subject to datum error. Try that with a GPS.

Capt. Tom
I have taken a number of boats over to the Abacos over the years. An owner of a big Hatteras impressed me with his nav station instraments. In the process of getting across the banks the GPS indicated a course that would have taken us across the end of Angelfish Point. After some discussion we altered course to avoid this obvious failing of the nav system to recognise dry ground. There is no substitute for an alert helsman. Electronic navigation is just an addition to prudent personnel.

Skip Strong
As someone who spends 200+ days a year on the water moving big ships around, I find differential GPS an incredibly useful tool for moving vessels safely from point A to Point B. As soon as land starts to get close a radar is the best tool to have for coastal navigation. It is easy to take ranges and bearings from the radar and plot them on a paper chart and know exactly where you are. It doesn't matter when the information was gathered for the chart, since it was all done visually to begin with. For those with more advanced radars, parrallel indexing is an easy way to set up a safe passage around a piece of land. One more big advantage a radar has over GPG; it shows other targets (vessels). On more than one occasion I have watched a vessel on radar moving at 20 knots in zero visibility safe in their assumption that since they have GPS and know exactly where they are it is ok to go that speed. With out radar they have no idea they are headed for a zero CPA with me. All this being said, I'm a big fan of technology and one of the best tools out there combines GPS, radar and AIS all in one package. Just don't forget to stick your head out the window once in a while to look around.

Metigar
We have a Hunter 420, and have also chartered in the Abacos (and elsewhere). We always have a paper chart in the cockpit. In the Abacos, that is usually Dodge on short hauls and the larger charts for longer runs (such as from Florida). We also use handheld GPS. Our new one is the Garmin 60C. We kept the Old GPSIII and even have an old GPS II we got for free somewhere. Redundancy is the name of this game. Also, by using handhelds, the cost is lower and we can get a new one every few years and get the new technology. No, they are not "as good as" a plotter, but in conjunction with paper charts do the job. Dr. Ralph is so right about the need to keep a sharp lookout. The charts are sometimes wrong -- very wrong. The nice thing about the 60C is that is has 58 MB of memory, so we can input lots of good chart data, even from the Garmin Blue Chart CDs for areas where we need that detail. For most purposes, the cheaper Garmin CDs (Waterways and Lights) are just fine.

SamFamAustin
I'd like to say that it really was a technologic breakthrough to have a computers put radar, depth sounders, GPS, plotters, and other stuff together in one unified package (common bus). It took 50 years to do this, and look for hand-held within the next few years. It is simply amazing. That said, unless there is a big storm or on-board problem I would NEVER recommend running into port at night, even with a good map guide and a full moon. It is bad luck on top of being risky. That is why commercial fishermen always leave at sunrise and come back (maybe a different day) before dusk. If you're on the outside at night you have three options. You can anchor, which may be difficult in deepwater off Abaco. You can set a sea anchor, a parachute or funnel canvas thing that slows your wind and wave drift (I like these a lot on small boats in small seas). Otherwise, you should beat to windward or wear to leeward and stay the heck away from land. Making landfall at night is extremely dangerous because you can't see the shoals and reefs and such. Distances are hard to judge. Maps can be wrong. Even radar will show clouds instead of real land and you can't tell which is which. You can't see the color of the waters, indicating depths. I would rather park on a messy 12-foot chop than end up on the hard in the middle of the night.

Big Fish
I just had an interesting experience during my crossing from Abaco to Jupiter FL. My entire panel went blank several times during the trip. A very good example of why one should know how to navigate the old fashioned way. It's nice to be able to use a compass and a chart. Unfortunately, Bahamas charts (except Dodge maybe) are even less accurate than GPS. The instruments were working properly when I arrived at Jupiter inlet. but unfortunately the GPS database did not show the inlet accurately. It showed land right across where the inlet actually exists. I suppose that's better than not showing land that IS actually there.Clearly, the consensus shows everyone knows that good old fashioned eye power and experience are the only really dependable navigational tools. I personally would never trust an instrument totally, whether GPS, radar, sonar, or anything else. I still think technology has made wonderful improvements to the boating experience. I really appreciate my color moving map GPS, color bottom sonar, color radar, remote control spotlight, two speed fishing reels, downriggers, oil injected outboard engines, and such. Most important is to use common sense and caution while gaining experience.

tmccaffery
The problem is that so many navigators who learned our craft in the past 20 years or so have come to believe that visual fixes and other "old fashioned" methods are "quaint" but no longer relevant. They also forget that the sea is unforgiving with even the most experienced navigators.

Abacoparrott
I personally like good, old-fashioned paper charts together with GPS (not chartplotter) coordinates. From reading this thread, I get the picture that the "chartplotter" section of the GPS is often in error, not the simple GPS fix. Soooo, in the past, in addition to dead-reckoning, I have used the GPS for present co-ordinates only and then transfered these co-ordinates to the paper chart. Then using the parrallel rulers to obtain the proper course line, I go to the compass rose to get the heading; overly simplistic maybe but works for me, and I feel comfortable with it.

Mr. Bill
Last month, our navigator used a laptop software package called 'fwigwi', (sp?), he said it was based on the explorer charts. (laptop had serial link to garmin waas-gps). My experience comming back from nassau thru gun cay, was the waypoints off the explorer charts were excellent, (and matched the chartplotter software: fwigwi), the bluechart americas chart plotter was off at gun cay channnel. (but right on at NW channel, and nassau harbor). The lesson learned was the explorer charts waypoints were pretty good. I now enter explorer waypoints (or DODGE's) into the chartplotter, and run the waypoints. & stop useing the chartplotter to get your waypoints. if the waypoints are correct, the gps is 'usually' correct. the problem is the overlay of the chart on top of the screen. The bluechart 'chart' had us over land at guncay. (but we were within 30' of land). as said before, If you have good waypoints, and enter them correctly, the gps will allow you to 'go to' the wp fine. Its the cart overlay that gets us in trouble, trust the waypoint (long/lat) #'s not the electronic chart. Most of the problems I've seen with the garmin charts are with land mass(es), not markers in open water. Like drRaplh said, theres some errors in digitizing the charts and converting to long/lat.

Noontide
We have two good uses for our chart plotters/GPS units: once you have succesfully navigated into a harbor etc. we save the trac and follow it when returning under poor to no visibility. This has never failed us. The other good use is as an anchor alarm.

S/V Toucan Dream
While anchored we and several other boats using the same software were shown on our plotters using NT chips on the ocean side of islands while the CD charts using the Capt'n or other PC based programs showed us in the correct place. Be careful.

Biggy
There are NO substitutes for paper charts.Anyone that ventures onto the ocean without them is foolhearty,Fog,heavy rain,electrical problems,all can ruin a otherwise good day.Depthfinder,wristwatch,compass,chart and an Eldredge where applicable,will always prevail.Once a captain forgets his or her basic training it is a recipe for disaster.

Boomer
My Dad started taking my family to the Abacos in a 21 foot Boston Whaler back in 197O. Back then, electronic nav aids were big, expensive, and unreliable. The nautical charts availbale were not that great either. Dad taught my brothers and me how to dead reckon with a chart, a watch, and a cheap hand held compass. But the most important thing he taught us is that if your not sure where you are and how deep the water is, stop the damn boat until you figure it out. I've made better than sixty trips to the island since 1970 and now own a big sportfishing boat with have electronic gadgets up the ying yang. I've got an interfacing radar / sounder / plotter system that will darn near back my boat into the slip if I program it to do so. The technology never ceases to amaze me, but it also gives you a false sense of security. Every year I see guys with better equipment than mine sitting hard aground, or worse, because they were to busy pushing buttons and watching the screen. My advice to Abaco newbies is to learn how to read the water and the charts before you learn how to program the plotter. But most importantly, if your gut tells you that you're not really sure how deep the water is and what lies ahead, stop the damn boat.

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