47) Radar

Radar

     12.07.05 between Islas Canarias & Barbados, Atlantic Ocean (circled: large freighter 4 miles away on the horizon)

An important aspect of passage making is collision avoidance.  Even though at times we are technically a sailboat since the motor is off and we have right-of-way we still have to look out for other vessels.  It becomes something to do when all there is out there is water and sky.  Since leaving The Canaries we have not seen very many other boats.  We use the radar at times to detect vessels on the horizon and get confirmation.  But, we have progressively reduced using it to not using it at all. 

During the night we are able to see the lights of the vessels when they are on the horizon.  During the day we are able to see the vessels.  The horizon line where the water meets the sky is approximately 4 miles from our point of view looking from the boat.  Sitting in the cockpit our eye level is about 10’ above the water and that determines a range of how far we can see.  The radar on this boat is located on the mast at the lower spreader about 25’ above the water line and looks forward.  There is a noticeable flat spot in the image of an area aft of us due to the mast blocking the array. 

Chuck drinks coffee to stay awake at night while the rest of us sleep after taking our baths and watching movies.

Radar Gun

Radar guns are used to detect speeding motorists.  Here, a gun transmits waves at a given frequency (shown in blue) toward an oncoming car.  Reflected waves (shown in red) return to the gun at a different frequency, depending on how fast the car being tracked is moving.  A device in the gun compares the transmission frequency to the received frequency to determine the speed of the car.  In this case, the high frequency of the reflected waves indicates the motorist in the red car is speeding and is probably about to receive a ticket.

U.S. Air Force

Radar Screen

Radar displays indicate the presence and movement of objects out of the range of vision, which is particularly useful for navigators.  Electronic equipment records the behavior of radio waves projected by the vessel; waves which do not encounter anything simply disperse, while waves bounced back reveal the shape and position of all objects in the region.  The characteristic sweep of the radar display occurs because the area is continually reassessed for new information, and the screen is reprinted in response.

   

We detect most of the large freighters when they are still 10-15 miles from us due to the very tall superstructure they carry.  It seems they have been seeing us and making collision avoidance moves.  That got us to speculating what the odds were if we tried to hit them on purpose on the high seas.  We think it is not possible.

At night it is very easy to determine if the lights are a freighter because of their relation to each other and we rely on this.  Below are some graphs that help boaters follow the rules of the road at sea.  The light colors on the graphs below are incorrect and were changed when I converted the files.  The white dots are in fact white; green dots are green; blue dots are actually red.