The Little Ship Club hosted the Small Craft Group’s evening presentation by Bob Bradfield at its London Headquarters on 17th. January. Bob specialises in producing charts of areas in the West Coast of Scotland that are not recently surveyed by UKHO or inadequately detailed for yachtsmen seeking out of the way anchorages.
Bob explained that the West Coast of Scotland is a wonderful area to sail and explore, especially if you can choose your weather. He had been sailing in high latitudes but then realised that he did not need to go so far to find excellent anchorages and scenery.
But why the West Coast of Scotland? Firstly, it is a huge area, some 125 nm x 300 nm, with most of it sheltered from ocean swells. There are sandy beaches and rocky coves surrounded by magnificent hill scenery. Add to this the number of small channels and anchorages and, of course, there is an abundance of wildlife. However, there were no charts suitable for yachtsmen of these inshore areas. So, he decided to make his own.
The UKHO standard charts of the area, Bob explained, were fine for passage making from island to island, but they lacked the detail for more adventurous sailing and accessing small, isolated coves. Even Pilot Books, although better than standard charts, gave only sparse information. The Clyde Cruising Club pilots and Imray charts were fine for a sunny day with good visibility but could let you down in rain or on a foggy day, with recommended transits between a building and the background hills being hidden.
UKHO charts of these inshore areas were often drawn from very old surveys, often from the 19th. century done by lead line. When these were made the positioning technique was far from the accuracy expected today and there were occasional omissions or misrepresentations. We were show a UKHO chart from1985 (not so old as some) and a comparison with its correction – a 0.7 metre sounding lurking in a 5.2 metre area!
To make a chart Bob starts with Ordnance Survey details of the shore and HW line as a background. He then surveys this basic outline with a single beam echo sounder using DGPS for accurate positioning. Extra detail is added to the chart as it is found. A final check is made with side scan sonar. At the same time a tide gauge is set up on a prominent solid location so that accurate tidal heights can be determined. Once tidal heights have been reduced to soundings all the data can then be incorporated into the new chart.
The Antares charts, which only cover the inshore areas explored by yachtsmen, can be run on a computer (PC or Mac), on tablets, a chart plotter or even a mobile phone. Even those without internal GPS can be used if connected via Bluetooth to a separate GPS receiver. Bob recommends the use of the Memory Map app to run his charts, although other apps can be used.
Things to be aware of:
He issues a warning that the charts have been produced by unqualified yachtsmen and suggests there will be errors – beware, use carefully, he says.
When using the charts, things can happen too quickly and GPS can lag or even stop updating. Proceed slowly when in confined waters close to shallows or rocks. He suggests that large scale charts in chart plotters plus strong tides can quickly produce a dangerous situation. In other words, use carefully and proceed with caution!
Bob concluded by showing a UKHO chart of the area around Dunstaffnage which was alongside his own chart. He indicated five significant differences between the two, differences that could be a problem to a yacht.
A full list of the electronic charts in the package which is available for sale (and updated annually), and much more information, can be found on the web site:
http://www.antarescharts.co.uk
The talk was greatly appreciated by the audience, which then went to dinner in the Little Ship Club. You can watch the recording of the presentation on the
Little Ship Club's YouTube Channel here.