Modern electronic charting on multifunction displays is a powerful tool for the voyager — they can know position and other navigational info just by glancing at a screen. With position data provided by GPS, and with some installations buttressed by input from the Galileo, the European analog of GPS, electronic chart navigation is accurate and convenient. In certain situations, however, voyagers can improve their navigation awareness and avoid possible problems by using tools that are a part of the electronic chart toolkit, but which might be turned off.
In order to declutter the screen and show those elements a mariner most wishes to see, an operator has many choices for the mix of elements shown. Depth contours, soundings, light characteristics, traffic separation zones, vessel performance data, and more can be toggled on and off.
In a recent blog post, navigation expert David Burch, the founder of Starpath School of Navigation and author of numerous books on navigation and weather, discusses this issue of choosing the right mix of tools for the situation and he focuses on the grounding of the ship Ever Given in the Suez Canal on March 23, 2021 (davidburchnavigation.blogspot.com/2022/05/NOVA-note.html). Now, it’s true that the difficulties of maneuvering a ship in a narrow canal are not exactly analogous to the maneuvering requirements of the average voyaging boat. The point that Burch makes is well taken, however. Following Burch’s advice will help voyagers in many situations when a voyager is in restricted space or shallow depth and is being affected by high winds or strong current.
First, let’s review the concepts of heading (HDG) and course over the ground (COG). A boat’s HDG is, of course, the magnetic direction in which the bow is pointing. COG, is the boat’s actual track over the ground. Given a situation with no current and given a powerboat operating without any wind, or a sailboat making no leeway (in reality all keelboat sailboats lose some ground to leeway — except perhaps a boat equipped with lifting foils), then a boat’s HDG will be the same as its COG. In the real world, however, boats are affected by current and wind and so a vessel can be pointed on a certain heading, and yet its COG can be considerably different. To counteract this, the boat needs to be steered at a heading that makes up for the ground lost to the current and wind. Since GPS can accurately fix a vessel’s position several times a second, it is easy to calculate a boat’s COG over time. And with heading info provided by an electronic compass, an electronic chart determines HDG. These two parameters can be fed into an electronic chart program and displayed both as alphanumeric data and also as lines that extend from the vessel symbol. The HDG line shows where the vessel is pointed. The COG line shows where the vessel will be in, say, two minutes. This elapsed time parameter, and thus the length of the line, is generally user selectable.
Burch has analyzed the Ever Given accident in four separate videos posted to YouTube that are well worth watching (the first video is here: www.youtube.com/watch?v=kQzomgjdtI0). In his video reconstruction of the accident, Burch used available data and inserted a wind component at 160 degrees. He also added the ship’s HDG and COG lines. The addition of these lines provides immediate visual info on where the ship is pointed, but, more important, where it is actually going. And the lines show that the vessel was standing into trouble because it was not correcting for the substantial wind effect on the ship’s bluff surface area.
Burch’s latest blog post on the incident was prompted by an episode of the PBS TV science series NOVA, Why Ships Crash (www.pbs.org/wgbh/nova/video/why-ships-crash/). While Burch writes that the TV episode does provide useful information, he focused in on one aspect of the show and how it failed to provide an insight into a useful practice when using electronic charts.
Specifically, Burch discusses how the video doesn’t show the vessel’s HDG and COG lines in its electronic chart depiction of the accident. “My main goal here… is to stress that the detailed NOVA study did not include the most important demonstration and conclusion of our analysis, meaning our proposed way to use standard electronic chart tools to monitor the navigation underway that may have prevented the accident in the first place. Namely, the display of both the heading line and the COG predictor line, so that the navigator would have immediate awareness that they were not going the way they were headed.”
Burch’s videos and his blog post are great for voyagers to view and read. They make the point clearly that turning on the HDG and COG lines in your electronic chart program can provide voyagers with valuable situation awareness and might help keep your boat off the rocks. n