Marine Radar

If you boat in New England, there will be times when you can’t see 100’ feet away from your boat.  Hopefully this will be while you’re at the dock.  If not, you will want to have and to know how to use a marine radar display. You’re visibility can be limited by many different factors, certainly fog is the biggest but there are others. Rain, snow and even smoke can cause limitations. The other condition you will find radar useful in is darkness.  Although not considered a limitation to visibility in the NAVRULES, it can certainly wreak havoc on a skipper in an unfamiliar port.  Modern Marine Radar can be a very precise instrument when installed and used properly.  It has the ability to show you what is around your boat in just about any of the conditions listed above.  Let’s first understand when to use the radar. NAVRULES states that any boat equipped with a working radar system must use it at all times, you may question this practice but it is the law.  It is really considered a secondary means of keeping a lookout (another must have NAVRULE) like the rule requiring you to monitor VHF 16.  When experimenting with your radar, I find that my students can learn better on a clear day when there is very little stress level and great visibility.  This way they can really begin to understand what it is they are looking at.  The display shows your boat in the center and the targets around it.  The “targets” are things that reflect the microwave energy back to your antenna.  Be careful here as not all objects do this, the lower they are in the water or the more energy they absorb, the less of a return you will get.  For instance, a nun or can buoy will typically show up very well where a kayak or sandy beach may not.  The targets are displayed within “range rings” that are spaced by the user at predefined distances. Each ring has a value which is typically indicated on the information bar at the top, bottom or sides of the display depending on the manufacturer.  If the range rings are set ¼ mile apart, and you have a target on the edge of the third ring, you know the target is ¾ miles away.  You will also have a line that runs from the center usually to the top of the screen.  This is the EBL or electronic bearing line. With this, you can determine where the target is in relation to your boat.  If we use the example above and place that target at the 10 o’clock or about 300 degrees from our bow, we know the boat is on the port bow, ¾ of a mile out.  Now we add motion, let’s say the target is moving towards our EBL (the direction we are traveling), we now have a potential for a collision depending on speed of travel for both vessels. This is what a prudent skipper would be looking for in the fog or other types of limited visibility.  With today’s modern equipment, you can integrate an electronic compass and GPS (Global Positioning Satellite) information to give you information on the movement of the other vessel.  In our example we determined there was a vessel at 300 degrees relative to our bow crossing our path. But when would it happen and where?  If you use integrated electronics, you may have an option called ARPA or Automatic Radar Positioning Aid.  This is very similar to what you may have seen in the movies where someone is marking dots, tracking a submarine or ship on a glass screen at timed intervals.  The electronics can sense which way the target or vessel is going and how fast and also give you the time when you will come in contact (hopefully not).  There are thousands of variables that can occur at any time on the water and many different ways to read and interpret the marine radar display information.  Depending on the brand, type of antenna and screen you may or may not have all the described functionality listed above.  There is much more to it than I can do justice with in this blog so I suggest you take a class, read a dozen books this winter or hire a captain who can train you on your equipment.  The last thing you want to be doing in the fog is reading the instruction manual.

Categories: Captain John's Log