Cutting through the fog

From Ocean Navigator #118
November/December 2001
There are many times when radar is an invaluable tool, when electronic eyes that see through night and fog can make all the difference. Good radar and the skills to use it properly should be a standard item on your voyaging list.

As night falls, or in the fog, the voyager quickly grasps the value of radar for collision avoidance.
   Image Credit: Bill Biewenga

A perfect example of the value of radar is a recent Vineyard Race (from Stamford, Conn., out Long Island Sound to Martha’s Vineyard, Mass., and back). As we made our final approach to the narrow waters of The Race, at Long Island Sound’s eastern end, the tide was still slowly sweeping us through the gate, but it was about to turn. At 0200 and in dense fog, we had a very limited understanding of what kind of traffic was around us. And, given the fact that we had no radar, we were sailing blindly.

The call on VHF channel 16, from a tug pushing a barge toward The Race from the opposite direction, was more than a little unsettling. “Calling the vessel approaching The Race, be advised that we are closing quickly and request that you assume a more southerly heading,” called the captain of the tug. His request was for us to take a course directly into the wind. After chatting a bit, we explained our situation. With less than a half-mile of visibility and closing quickly with an unseen target, it occurred to me that it might be a good time to charge the batteries and have the engine running. The tug, with his barge, certainly wasn’t going to be able to stay out of our way, and it wasn’t his responsibility in any case. We had to be as prepared as possible for a close encounter in order to avoid unwanted consequences. With all eyes peering forward through the foggy blackness, looking for approaching running lights, it became obvious in a visceral sort of way that good radar and an understanding of how to use it can be invaluable on a boat – just about any boat.Many radar models available

Fortunately, a variety of manufacturers make good radar available for many marine needs. We may or may not need all of the newest bells and whistles, but it is good to know what some of them are as well as understand what some of the more commonly used features might be. I have frequently used Raytheon’s models. July of 2001, I used Simrad radar on a passage through the North Sea and Scotland’s canals. And aboard our trimaran Great American II for our speed-record attempt to Melbourne, Australia, we have a new Furuno radar unit. Any of those radars would have been a blessing as we sailed through The Race, but some have more features and adaptability than others do.

Image Credit: Raytheon

Most radar units, like this Raytheon unit, have a wide range of features. To use them effectively, radar users must invest time in learning and practicing with their radars.

Rightly or wrongly, I think my basic requirement for radar is that it be simple and straightforward. I would like it to be relatively easy to use and understand with user-friendly software. I know that I should read the manual, but the fact is that I seldom sit still for that long. If I were buying one radar for use on my only vessel, I would probably spend more time learning all about its various capabilities. But since much of my time is spent on a variety of vessels, my preference is to be able to sit down, turn it on and learn the major features in 15 minutes or less. Now, as I start to explore some of the features offered in the latest generation of radar, I begin to realize that time spent exploring the full potential would be well invested.A radar wish list

Some of the things I like to see in a radar unit include screens that are clearly visible in daylight and can be dimmed down low enough to allow me to retain some degree of night vision while using a radar unit in a cockpit at night. I want to be able to control the radar’s features whether the unit is in the nav station or a secondary unit in the cockpit. If I need to zoom into another level to find a landmark or buoy, I don’t want to have to jump down to the nav station and then run back up on deck to see if I can pick up a buoy visually. There are times when I have better things to do than run back and forth to get complete information. I would also like to have enough clarity from the unit to be able to discern the difference between rain and a land mass and for the tuning controls to be easy to use. And I would like to have the unit mounted properly so that I can get maximum useable range from the radar. The operator’s manual of Furuno radars explains that “the maximum detecting range of the radar varies considerably depending on several factors, such as: the height of the antenna above the waterline; the height of the target above the sea; the size, shape and material of the target; and atmospheric conditions.” It continues: “Under normal atmospheric conditions, the maximum range is equal to the radar horizon or a little shorter. The radar horizon is longer than the optical one by about 6 percent because of the diffraction property of the radar signal. Rmax is given in the following equation, where Rmax is the radar horizon in nautical miles, h1 is the antenna height (in meters) and h2 is the target height (in meters):


Gone are the days of displaying just echoes on the screen. Today’s units can show all manner of integrated data.

Rmax = 2.2 x (square root of h1 + square root of h2)

For example, where h1 is 9 meters and h2 is 16 meters:

Rmax = 2.2 x (3 + 4) = 15.4 nm

On the face of it, that appears rather straightforward. Mounting of the unit, however, can mean the difference between seeing 15.4 nm and considerably less. The radar antenna needs to be reasonably level in order to achieve those kinds of ranges. If the antenna is fixed to the mast, there may be sufficient height, but the range can be substantially reduced when the boat heels over 25°. If the antenna has a convenient means by which it is leveled, the range of the unit will be considerably enhanced.

When I know that the radar is properly aligned with the bow of the boat, the antenna is straight, and the unit is properly tuned, I can begin to have some faith in what I’m seeing on the radar screen. The features I most commonly use are the EBL (electronic bearing line), rings, and VRM (variable range marker). The EBL gives me a bearing to a target at a particular point in time; the rings provide a fast reference point to a target; and the VRM marks the range to a target at a particular point in time. As time elapses, I can easily see if we are gaining or losing range and bearing to a target. Are we on a collision coarse with another vessel as we maintain the same bearing but continue to close range? Are we being swept to the wrong side of a buoy by a current or tide even as our compass heading implies that we are aiming toward the correct side of the buoy? The EBL and VRM will give you the answers.New technology

These are some of the traditional ways that radar has been used. But new technological combinations are about to add to our uses as well as to the conveniences. Some manufacturers have already come out with these features and others may soon. Recently, Furuno introduced its NavNet system. Various models and data sources can now be linked together using a LAN cable and an Ethernet 10/100 Base-T Hub, equipment that is available through any computer outlet. The system integration allows GPS, network sounder and up to four display units to be networked together. Any of the units can control the system, allowing for units on the fly bridge, in the nav station or in the cockpit to be controlled independently. Various units can be connected to each other allowing large-screen displays in the nav station and smaller units in other areas. A PC can even be interfaced with the system, allowing for uploading and downloading of waypoints and routes as well as other functions that can be jointly shared or expanded.

Many of the new radar display units also act as plotters. In most of the units, the plotters have separate windows in which Navionics, C-MAP or other charts can be displayed next to the radar window. In some models, such as the Furuno 1833C, radar can be overlaid directly on the chart. While this feature may not always be completely suitable as the only means of navigation, it can certainly help the occasional user identify land features, buoys and other targets. In the past, I’ve gone through narrow passages in the middle of the night using separate radar and plotter screens. If the chart data is somewhat inaccurate or not in agreement with the data used by the GPS, the plotter can give a less-than-accurate track. Using radar helps to eliminate some of that inaccuracy. Having them both on the same display goes a long way toward helping the night navigator know exactly where he is and exactly where he’s tracking as he checks other nav information sources for confirmation. It should be noted that the high-end radar/plotters require a good source for heading information. While the companies providing the radar can also provide high-speed heading sensors, other manufacturers, such as KVH, also have their own stabilized compasses.Displaying video images

Image Credit: Raymarine

In addition to integration with GPS, electronic charts and sailing instruments, current radars also have bright, easy to read, daylight color screens, soft keys for customizing the display and automatic gain, sea clutter and tuning control. Voyagers can get so much more capability than just a few years ago.

Many of the latest generation of radar displays also allow for the simultaneous display of video images in a separate window. While it may seem frivolous to be able to watch DVDs while sailing or powering along, that’s not the only use for video. Aboard Zaraffa, a Reichel/Pugh 66-footer, a video camera has been fitted to the speedo transducer through-hull fitting. The camera can be rotated around not only to see dolphins swimming beneath the boat but also to check the keel and rudder for debris. The video can play constantly in real-time and show up on the navigator’s radar/video plotter.

Chatting with the captain of Zaraffa, Rodger Erkker, I found that use both interesting and helpful, but I found one of the other uses for the video even more interesting. Connecting a “lipstick” camera to a 200-foot length of lamp cord, they used one strand to carry power and the other strand to carry data from the camera to the video display. They then taped a small flashlight to the lipstick camera. Lowering the camera and light down into the mast, they could inspect the inside of the rig to insure that there were no wraps in the halyards or chafe points along the inside of the rig. All of this data can be viewed on the same radar/video plotter that shows the navigator the location and size of squall lines that are approaching, and it gives a definitive range and bearing of a particular buoy.

During the 1993 Whitbread Round the World Race, S/V Winston approached an iceberg in the middle of a dark, foggy night south of Newfoundland, Canada. A crewmember happened to check the radar at a critical moment and saw a target about four miles directly ahead. After passing the iceberg safely and leaving it to port, we thought it prudent to send someone below 20 minutes later. He came back to report that there were now seven icebergs on the radar screen, all of which were farther to port than the first target.

Had we inadvertently left the first target to starboard, we would have stumbled into a dense iceberg field and may not have noticed them on the radar until we were surrounded and it was too late. Automating the observations and having a human oversee the radar can go a long way toward avoiding obstacles.

Features provided by the latest generation of radar plotters also provide convenience. One manufacturer employs a common user interface with all of its models. If an owner decides to have one type of radar display in the nav station and perhaps a smaller display in the cockpit, both use the same set of controls. Display pages can often be customized, which provides the navigator with the information he wants in a format he finds convenient. The radar/plotter information may be displayed with the vessel’s heading toward the top of the display. In other cases, the navigator may prefer to have north up to coincide with other charts, and in still other cases, the navigator may prefer to have course up at the top. For vessels with power consumption considerations, some models offer different types of screens and varying consumption rates.

All of these features come at a price, however. And the price isn’t only in terms of how much a unit costs. Some of the units I’ve used have apparently had relatively slow CPUs, leading to delays in pulling up the relevant information on the screen. Some units have difficult or non-intuitive controls, and some of them use a speed log rather than a GPS for their speed input. In a current or tidal flow, the rate of advance can be off significantly. In any case, it’s always best to know what your data sources are and how they may limit the accuracy of the data output.

As we negotiated The Race that dark and foggy night during the Vineyard Race, it became all too obvious that there are a number of ways to reach one’s destination under trying circumstances. Peering into a thick fog is one way. Having reliable, current generation radar that is properly installed with accurate, appropriate data input is another way. In retrospect, I would think that having and knowing how to use radar is probably a better way. And I would guess that the captain on the tug that night would probably agree.

When I know that the radar is properly aligned with the bow of the boat, the antenna is straight, and the unit is properly tuned, I can begin to have some faith in what I’m seeing on the radar screen. The features I most commonly use are the EBL (electronic bearing line), rings, and VRM (variable range marker). The EBL gives me a bearing to a target at a particular point in time; the rings provide a fast reference point to a target; and the VRM marks the range to a target at a particular point in time. As time elapses, I can easily see if we are gaining or losing range and bearing to a target. Are we on a collision coarse with another vessel as we maintain the same bearing but continue to close range? Are we being swept to the wrong side of a buoy by a current or tide even as our compass heading implies that we are aiming toward the correct side of the buoy? The EBL and VRM will give you the answers. New technology

These are some of the traditional ways that radar has been used. But new technological combinations are about to add to our uses as well as to the conveniences. Some manufacturers have already come out with these features and others may soon. Recently, Furuno introduced its NavNet system. Various models and data sources can now be linked together using a LAN cable and an Ethernet 10/100 Base-T Hub, equipment that is available through any computer outlet. The system integration allows GPS, network sounder and up to four display units to be networked together. Any of the units can control the system, allowing for units on the fly bridge, in the nav station or in the cockpit to be controlled independently. Various units can be connected to each other allowing large-screen displays in the nav station and smaller units in other areas. A PC can even be interfaced with the system, allowing for uploading and downloading of waypoints and routes as well as other functions that can be jointly shared or expanded.

Many of the new radar display units also act as plotters. In most of the units, the plotters have separate windows in which Navionics, C-MAP or other charts can be displayed next to the radar window. In some models, such as the Furuno 1833C, radar can be overlaid directly on the chart. While this feature may not always be completely suitable as the only means of navigation, it can certainly help the occasional user identify land features, buoys and other targets. In the past, I’ve gone through narrow passages in the middle of the night using separate radar and plotter screens. If the chart data is somewhat inaccurate or not in agreement with the data used by the GPS, the plotter can give a less-than-accurate track. Using radar helps to eliminate some of that inaccuracy. Having them both on the same display goes a long way toward helping the night navigator know exactly where he is and exactly where he’s tracking as he checks other nav information sources for confirmation. It should be noted that the high-end radar/plotters require a good source for heading information. While the companies providing the radar can also provide high-speed heading sensors, other manufacturers, such as KVH, also have their own stabilized compasses.Displaying video images

Image Credit: Raymarine
In addition to integration with GPS, electronic charts and sailing instruments, current radars also have bright, easy to read, daylight color screens, soft keys for customizing the display and automatic gain, sea clutter and tuning control. Voyagers can get so much more capability than just a few years ago.

Many of the latest generation of radar displays also allow for the simultaneous display of video images in a separate window. While it may seem frivolous to be able to watch DVDs while sailing or powering along, that’s not the only use for video. Aboard Zaraffa, a Reichel/Pugh 66-footer, a video camera has been fitted to the speedo transducer through-hull fitting. The camera can be rotated around not only to see dolphins swimming beneath the boat but also to check the keel and rudder for debris. The video can play constantly in real-time and show up on the navigator’s radar/video plotter.

Chatting with the captain of Zaraffa, Rodger Erkker, I found that use both interesting and helpful, but I found one of the other uses for the video even more interesting. Connecting a “lipstick” camera to a 200-foot length of lamp cord, they used one strand to carry power and the other strand to carry data from the camera to the video display. They then taped a small flashlight to the lipstick camera. Lowering the camera and light down into the mast, they could inspect the inside of the rig to insure that there were no wraps in the halyards or chafe points along the inside of the rig. All of this data can be viewed on the same radar/video plotter that shows the navigator the location and size of squall lines that are approaching, and it gives a definitive range and bearing of a particular buoy.

During the 1993 Whitbread Round the World Race, S/V Winston approached an iceberg in the middle of a dark, foggy night south of Newfoundland, Canada. A crewmember happened to check the radar at a critical moment and saw a target about four miles directly ahead. After passing the iceberg safely and leaving it to port, we thought it prudent to send someone below 20 minutes later. He came back to report that there were now seven icebergs on the radar screen, all of which were farther to port than the first target.

Had we inadvertently left the first target to starboard, we would have stumbled into a dense iceberg field and may not have noticed them on the radar until we were surrounded and it was too late. Automating the observations and having a human oversee the radar can go a long way toward avoiding obstacles.

Features provided by the latest generation of radar plotters also provide convenience. One manufacturer employs a common user interface with all of its models. If an owner decides to have one type of radar display in the nav station and perhaps a smaller display in the cockpit, both use the same set of controls. Display pages can often be customized, which provides the navigator with the information he wants in a format he finds convenient. The radar/plotter information may be displayed with the vessel’s heading toward the top of the display. In other cases, the navigator may prefer to have north up to coincide with other charts, and in still other cases, the navigator may prefer to have course up at the top. For vessels with power consumption considerations, some models offer different types of screens and varying consumption rates.

All of these features come at a price, however. And the price isn’t only in terms of how much a unit costs. Some of the units I’ve used have apparently had relatively slow CPUs, leading to delays in pulling up the relevant information on the screen. Some units have difficult or non-intuitive controls, and some of them use a speed log rather than a GPS for their speed input. In a current or tidal flow, the rate of advance can be off significantly. In any case, it’s always best to know what your data sources are and how they may limit the accuracy of the data output.

As we negotiated The Race that dark and foggy night during the Vineyard Race, it became all too obvious that there are a number of ways to reach one’s destination under trying circumstances. Peering into a thick fog is one way. Having reliable, current generation radar that is properly installed with accurate, appropriate data input is another way. In retrospect, I would think that having and knowing how to use radar is probably a better way. And I would guess that the captain on the tug that night would probably agree.

Categories: Navigation