Developing Navigational Safety-Critical Information for Bridges on Ships
Grounding and collision are threats to a safe trip. A captain needs to know exactly where the ship is, that it is on the planned route, and finally that close contact with surrounding traffic is avoided. In addition to watching the surroundings, the captain needs to monitor the radar and often an electronic chart display, as well as other instruments that show the state of the engines, etc. These displays provide vital information, but the managing of the displays may divert attention from the observation of surrounding waters. In stormy weather, the radar can become confusing and difficult to interpret. An echo, presented as a yellow spot on the display, can symbolize a small boat or a big wave; the latter is referred to as "sea-clutter." The radar has intelligent algorithms for reducing the amount of sea-clutter in such situations. While this functionality is effective, the user interaction with the equipment is inappropriate. A captain may have to go through several menus and choices in order to adjust the settings. If this interaction takes 30 seconds, a typical high-speed ferry at 40 knots advances 600 meters.
To determine which information is essential for safe navigation, I performed field studies on ferries of varying sizes in areas with different kinds of navigational settings and traffic. I performed one-hour interviews with ten captains of high-speed ferries on how they prioritize information sources and on navigational difficulties and accidents they had experienced themselves or heard of. According to the interviews, the captains gather the most important information from radar, electronic chart display systems, and from watching the surroundings. Therefore, I suggested that safety-critical information from present sources be integrated and displayed on the windscreen. Such a presentation would reduce the need to look down on and manage other displays, especially in situations where visibility is poor.
I decided to present a navigable channel, or fairway, on the windscreen, along with shorelines and symbols showing surrounding ships' position and heading. In the evaluation recently performed in our lab, three experienced captains assessed the merits of this setup. On the simulated windscreen, we displayed markings for a fairway, contours of shorelines, and the position and heading of surrounding ships. The captains drove a ship from a fixed starting point along a fairway for five minutes, while at the same time they had to overtake one ferry and meet another. They repeated this procedure seven times while weather conditions varied along with the brightness of the displayed information. After each "trip," they answered a set of 15 questions regarding their subjective opinion on the presentation; how it would affect their attention and behavior. The sessions were tape-recorded and transcribed.
The results from the first evaluation are positive and all of the captains liked the fairway presentation, agreeing that it gives a good perception of what will happen in the near future. Two captains maintained this attitude throughout the evaluation. At some point during the simulated trips, all the captains considered having safe water (that the water is deep enough) as a competitor to the fairway. One captain concluded that he would prefer to see safe water on the display. All those tested commented that fairways do not exist in all waters, but mainly in coastal waters and harbors. Furthermore, ships travel in fairways most of the time, but sometimes it is necessary to leave the fairway in order to avoid a collision or some other danger. Boundaries for safe water, in combination with the predetermined route, might be sufficient as an alternative to displaying a fairway on the windscreen. The shoreline presented was in general too crude and intrusive, and the captains complained that it was flickering, too thick, and that the color was too bright (two captains, however, considered it important for the awareness of what would happen in the near future). After a modification of the design, a more extensive evaluation will be carried out.
|Modified 15 January 2003 * Contact Us|