I learned to sail before the introduction of electronic charts and chart plotters. In fact, I learned to sail before GPS was widely used on boats. As a student, many of my instructors might have been quite sniffy about the emerging technologies; what if you lose power and can’t run the systems? What if the Americans turn of the GPS or reduce its accuracy? Some instructors still are sniffy. We were all taught the good old-fashioned way; with paper charts, pencil, rubber and Portland or Breton Plotters. And rightly so, as the power could still fail, and the GPS signal could yet disappear.
Electronic chart data is simply based on the paper chart data, sourced from hydrographical surveys. The suppliers of electronic charts simply vectorise the information on the paper chart, so that different information is displayed or hidden, depending on how far you are zoomed in or out. It reduces clutter and presents the relevant information more clearly. But if the paper chart is incorrect, your electronic chart is also likely to be so. In short, just because it is electronic and modern, doesn’t make it more accurate.
One painful task with paper charts was chart corrections or updates. These were issued regularly in the UK, and the skipper had to go through the paper charts meticulously to make the published amendments with pen or pencil! With electronic charts, you simply re-download the data onto your chart to get the latest updates.
Some chart suppliers even have ‘community edits’ to allow users to add their own useful data, that may not have been formally surveyed. Obviously, there is some form of moderation or checking before these community data make their way eventually onto the golden copy of the chart. Otherwise people would be inventing underwater volcanoes just off Skegness.
A further issue is the incompatibility of the paper chart datum with GPS. For example, when we were sailing a chartered yacht in Turkey years ago, the chart plotter showed us sailing about 100m on the land, parallel to our actual track several hundred metres away! How? Well, the chart on the plotter was a rasterised reproduction of a paper chart, which was produced in a survey by Sir Francis Beaufort in the middle of the 19th century! This admiral and cartographer (of Beaufort Scale fame) didn’t have sophisticated GPS surveying technology, so his paper charts are not quite as accurate as modern surveyed charts. The GPS is telling you where your yacht is within about 10m accuracy, but Sir Francis might have been a few hundred yards out when he was drawing the Turkish coastline.
So, don’t always believe what you see. Further, especially outside UK waters (which are very well surveyed), even the most detailed charts won’t have every single visible rock or shallow, underwater hazard mapped. So, it pays to be cautious.
When Alix and I sailed in the Whitsunday Islands about 20 years ago, the most important bit of kit was a pair of polarized sunglasses, with someone posted on the bow to look out for reefs. Polarization enables you to see the reefs through the water. Without them, you just see the sun and sky reflected on the surface. In clear waters, if you can see the bottom, you are probably in less than 10m of water. In general, if you steer towards the land, the water will get shallower and vice-versa, but that is simply a generalisation that does not always apply, especially if there is an unknown underwater rock just a little further offshore.
Today, young mariners in the Mediterranean actually use Google Earth to help navigate into anchorages, because the incredible satellite imagery, can highlight underwater typologies and potential hazards. Of course, in murky waters, or if there are ripples on the water, or if the sun is in the wrong angle, the satellite imagery is obscured and not that helpful.
We always have large scale charts from Imray on Missy Bear, normally paper, but increasing downloaded onto iPad. But these are for passage planning, and cannot include a great level of detail. Detailed paper charts, of much greater detail over a much smaller area, are available, but these are expensive (30 Euros each). And you would need to buy, store and update hundreds of them to cover the area through which Missy Bear is transiting.
The only realistic, practical solution is to buy electronic charts, and a good chart plotter. So, we have spent nearly £250 on an SD card from Navionics (a supplier of electronic charts). It is the +43XG Mediterranean and Black Sea, and includes detailed charts for the area between the Azores in the west and Georgia in the east. When zoomed out on our expensive BandG Zeus 3 touchscreen plotter, the chart just shows the coastline and the islands. But when zoomed in fully, it shows the rocks, depth contours, marina pontoons, fuel pumps etc, for every place in between.
The charts only present point or line data. They do not guide you into unfamiliar waters. For that, one normally buys a Pilot Book of the area. Rod and Lucinda Heikell, who I mentioned in a previous blog post, have authored several Pilot books for areas of the Med. We are currently using their ‘Italian Waters Pilot’, which includes guidance on navigating safely around our next island stop; Sicily.
But these pilot books only really cover the main ports, marinas and anchorages and cannot, for reasons of space, include information on every bay.
For that, there are several Apps, that allow communities to rate individual bays and coves etc. and add whatever notes they choose. We use Navily, which also includes wind data up to 72 hours in advance, so that you know if the bay is sheltered now, and whether it will remain so, if the wind is forecast to change direction or strength. But these Apps are not really navigation aids.
The bottom line is that there is a lot of information out there, and that you should arm yourselves with several tools, and not rely on just one. Further, none of them is totally infallible, especially in areas of the Med that are less frequented, and perhaps not as well surveyed as the waters around the UK. It just adds to the fun and excitement! Doesn’t it?
When I was instructing, years ago, my students did run aground on a rock in the Solent, which was in highly visible area outside Yarmouth, and a tad embarrassing. I had hinted to them before that if they didn’t change what they were doing, that was a definite risk! But ultimately, that was my error for not stopping them. My colleagues giggled back at base, and told me that I should really tell the Admiralty about that rock. Endless fun.
One of my instructor colleagues, who was also a charter airline polite in the summer, anchored in mud for a winter lunch, after which his students realised that the keel was well and truly stuck in, as the tide had retreated. They had to wait several hours there for the water to return, stuck up like a lolly on a stick. Another red face!
In fact, as instructors, we were encouraged to push students to the limit. We made them navigate into the shallowest of creeks to test their ability to predict water levels at a specific location and at a specific point in the tide. The trick was to make sure that the exercise was in an area with a soft bottom, and that it was on a rising tide; if they did ground it, it would be a soft landing, and they would float off shortly afterwards.
There are several tricks that we taught Yachtmaster students, to getting a yacht off the bottom. I’m not sure that they are all taught now, for reasons of health and safety no doubt. The first is to try and go out the way you came in; blindly going forwards is likely to make things worse, not better. If you cannot move, you can try and drag your way out; put the spare anchor in the dinghy, row it our and drop it somewhere deeper, and then pull the yacht towards the anchor using the anchor warp.
You can also try and reduce the draft of the yacht by lifting the keel (some yachts actually have lifting keels, but most do not.) You would get a passing boat to take your spare halyard (a halyards runs from the top of the mast and use used to raise sails.) By taking the halyard and motoring away from the stricken yacht, the rescue boat pulls the top of the mast, which heels the yacht over and so lifts the keel, because the boat pivots vertically about its hull.
But if there is no friendly rescue boat nearby, the most fun to be had is as follows: centre the boom; get all your students to climb onto and sit astride the boom, like horseback riders in a row; release the mainsheet slowly and send the boom (and grinning students) out over one side of the yacht! Their weight (the bigger students the better) heels the boat and lifts the keel! [Ed, Alix has asked me to point out that she would be no good at that, as she weighs next to nothing.] Et voila! It’s probably this method that may be frowned upon now?
