Budget Electronic Charting

Electronic chart plotters offer many useful features, but the costs can be high, particularly when you buy charts in both hard copy and electronic form. David Kerr explores a cheaper alternative which still provides most of the benefits.

Scanned charts
Last year, a reader wrote to me in response to a brief article about computers on boats. He said that he had been using scanned charts in conjunction with free Chart Plotting software and that the results were impressive. He kindly sent me software, scanned charts and installation instructions. I was impressed by what I found and decided to use scanned charts on my own boat.

Computers on Pastime
We have used a laptop on Pastime of Sydney for more than seven years. The current one is still working fine after more than five years- a testament to the strong, padded, waterproof case and the laptop itself. We have not normally used a chart plotter or electronic charts because of cost and power drain. Most of the time, we use the mini-plotter screen and other features of the GPS. However, with the advent of ultra small vehicle computers and industrial flat screen displays, we have decided to upgrade to a fixed computer installation and will run chart plotting software from time to time. This evaluation was therefore very timely for our situation.

You can see from the diagram that the computer is linked into the GPS, Autopilot and AIS [Automatic Identification of Ships] controller so that the computer can plot Pastime's GPS position plus the positions of any ships over 300 tonnes (via AIS). The computer can also drive the autopilot as well as downloading and uploading route and way point information with the GPS. The charts are our own hard copy charts,  scanned in small sections, stitched together and calibrated before being stored on the hard disk. I have obtained legal advice which says that I can digitise and use my own charts in this way. However I cannot legally pass them to anyone else even if they own the same hard copies. Any reader should obtain his or her own legal advice in this matter.

Sailing in Europe
If you are sailing in Europe, there are large numbers of professionally scanned  and calibrated charts available for as little as A$2 per chart. These are derived from US charts which are not Copyrighted as in Australia and New Zealand. I purchased a couple of these charts to see what they were like and you can hopefully see from the screen shot that they are very usable.

SeaClear II
The chartplotting software- SeaClear II  is free and was developed by a yachtsman  over eight years ago. It has all the features of most commercial chart plotting software and has been regularly maintained and enhanced over a long period of time. It is being used by many yachties, particularly in Europe. In my extensive trials, I have found no problems, indicating that reliability is good. Indeed, I have found less faults in SeaClear than in three other commercial packages which I have previously used. Because SeaClear uses scanned charts, the data is essentially two dimensional. Thus, depth and height information are only available visually, unlike vector charts where the chart plotter can detect if you are sailing into what it thinks is shallow water. The quality of position information is also only as good as your scanning efforts, but I was more than pleasantly surprised by my scanning results.

What you need to scan charts
We already had what we thought was a good quality scanner so implementing SeaClear was  zero cost- apart from the labour involved in scanning and calibrating the charts.  The process involves scanning a large chart in sections (usually A4). You then need an image editing program; ours is Adobe Photoshop which came bundled with the scanner. Photoshop will also do a professional job updating charts with Notices for Mariners. I quickly found that this software MUST be able to rotate images in steps smaller than one degree. Indeed, by the time I did my second chart, I was sometimes rotating a section 0.03 degrees to get the verticals/horizontals true. I did this using Lat/Lon lines on the scanned section and scrolling them past the Photoshop's rulers. I also used Photoshop to crop each scanned section because the raised edges of the scanner introduced distortions at the edges. I have heard of sailors grinding off the edges of the scanner to make the top totally flat but my wife Penny (owner of the scanner) was not amused at that suggestion!

"Stitching" by computer
A program (CCS) is provided which enables you to build up a full sized chart on the computer by adding a scanned section at a time. You move the new section until it exactly lines up with the previous sections. The program lets you see underneath the section that you are moving so that it is possible to get extremely good alignment. Pressing a button then integrates the pieces.  CCS cleverly melds the pixels at the boundary so that often it is impossible to detect the join. I found that turning off the automatic brightness/contrast feature on the scanner helped match colours, particularly when a scanned section was partly land and partly water and being integrated with a total water or total land area.

Some traps for the speedy
Scanning is the crucial part of the process. I can scan a single page in 40 seconds so I mistakenly thought I could do a chart in about 30 minutes (10 sections at 40secs plus editing time of a few minutes per section). WRONG! My first chart took four and a half hours!  Consistently, I tried to cut corners by having insufficient overlap between the scanned sections. After cropping, I then found gaps- so back to the scanner I went. Occasionally, I was a little cavalier about getting the rotation of the sections "just right"- particularly over water. The next chart took two hours and with practice I believe one hour is possible. I consider two hours the "break even" point between convenience and cost of effort.

Things worked best when I scanned a large chart in 18 sections rather than the possible 10. The good overlap ensured nothing was missed and I could trim off any distortions at the edges. I quickly learned to scan three sections across then integrate them before scanning any more. I used 200 dots per inch for the scanning and this has proved a good compromise between quality and storage space.

Calibration
Once all the chart sections are assembled, it is time to calibrate them. I really enjoyed this (it's much more fun than the scanning) and I found it  simpler than I expected. Basically, you open up a chart in the MapCal program and then select as many calibration points as you need to make it line up with the original. I found it important to leave the Longitude and Latitude scales on the scanned chart for this purpose. These scales can then be hidden within the chart border for seamless use in SeaClear. I found that I could produce a chart that was as accurate as the paper original  used with decent plotting instruments. There is the added benefit that GPS corrections can be applied automatically. These are the corrections that I most often get wrong when manually planning routes with paper charts.

SeaClear II features
Finally, the charts are loaded into SeaClear where they can be zoomed and panned as in any other Chart Plotter. SeaClear also automatically jumps from chart to chart as you cross chart boundaries. I'm not going to describe all SeaClear's features in detail- you can read the manual (in many different languages) on the website. SeaClear has all the features you would expect in a full commercial package. There are almost unlimited routes and way points which can be downloaded to the GPS. Tracks can be converted to routes. Day and night viewing modes are very configurable. There are auto and manual logbook facilities and trip planning aids such as estimation of fuel consumption. Cross Track Error, time to way point and time to destination are all succinctly displayed. There are audible and visual warnings (e.g. for loss of GPS or off course situations). I have planned routes on it and downloaded these to the GPS. The interfacing is excellent and you should have no problem driving most autopilots or external display units  with NMEA inputs. As well as GPS, AIS and autopilots, you can connect Depth, Wind and Compass information if you have it available in NMEA format. On the down side, SeaClear does not yet perform Great Circle calculations. Seaclear handles BSB/KAP and GEO/NOS charts as well as your own scanned images.

A few at a time...
We have approximately 75 hard copy charts,  so I'm going to scan them "as needed" and a few at a time. It also makes sense to perform this scanning when charts are new and unwrinkled. The ones I scanned were well used but this did not significantly impact the final result.

Aerial Photographs
At the suggestion of the CH reader who started me on this investigation, I scanned and calibrated some of the aerial photographs from "100 Magic Miles" (the popular cruising guide to the Whitsunday Islands). Unfortunately, due to Copyright restrictions (the photographs are themselves licensed for the book from a Government agency), I decided not to reproduce these aerial photos in CH. Such aerial photography is becoming available on commercial Chart Plotters but you too can have it using SeaClear. What you cannot currently do is superimpose multiple images (e.g. photo and chart) on top of one another in SeaClear.

So, in conclusion, it is feasible and extremely economical to scan your own charts and then use them electronically provided you already own a suitable computer and scanner plus an image editing program. Like me, you will likely gain a lot of satisfaction from the process.

Boxes:
Useful web addresses
The SeaClear II website is  http://www.sping.com/seaclear
See http://www.1yachtua.com for cheap charts covering parts of Europe.

What is AIS?
AIS came into force Internationally on January 1st 2005. All ships over 300 tonnes are required to carry and operate AIS at all times the ship is under way, anchored , moored or berthed. Every few seconds, the AIS system transmits high speed data  duplicated on two independent VHF channels. Included are MMSI, latitude/longitude, speed, rate of turn, course over ground, heading, size of ship, name, call sign and destination as well as other less useful information. This means that a cruising yacht, equipped with at least AIS receive capability, can be very well informed about all shipping within many miles- indeed, well beyond the distance of most radars. It can even "see" around corners or over cliffs- provided the VHF signal can be detected. AIS equipment is still very expensive. However I have been able to build a small single channel AIS receiver and decoder which we have fitted to Pastime. We can leave the unit on all the time as the power drain is less than 0.05amps. The AIS sounds a warning when any ships are detected within 10NM and displays range, bearing,  position & all the other data mentioned above. It combines the AIS and GPS data before sending them to SeaClear II via a single RS232 connection. I have successfully"seen" ships over 90NM away with AIS. Increasingly,  chart plotters and PC chart plotting software now support AIS.

As the price comes down, more yachties will be able to install the same sort of equipment and this will be of great assistance both at sea and when navigating restricted or busy shipping channels.

Equipment we are using
Canoscan 1250U2F scanner. Adobe Photoshop Elements for initial scan post-processing. Vehicle computer CDT 615 from CDT technology in Victoria.  Logitech wireless keyboard and mouse. 15" Industrial flat panel LCD screen (ICP150W) from ICP Electronics in Sydney. AIS controller designed and built by myself. Garmin GPS76 and GPS75 GPS systems. Raytheon autopilots (including one driving the  Cape Horn wind vane). Wireless stereo interface from computer to the boat's sound systems.

Pics
1 Diagram of PC system using SeaClear
2 Getting the edges almost straight helps
3 A big book worked better than the scanner lid
4 Showing stitching by computer
5 It's hard to spot the joins
6 Scanned, calibrated charts are cheap for Europe
7 Spot the join- if you can!
8 A few wrinkles from a well used chart

Author Box:
David Kerr is a regular contributor to Cruising Helmsman. He and his wife Penny are currently preparing their Swarbrick S111, Pastime of Sydney, for the next voyage. This will include New Caledonia, Vanuatu, Solomon Islands and the Louisiade Archipelago. David is also an electronics design engineer.