By Frank Patton/Lowrance Pro Staff
Introduction

You might wish to review or reread the part 1 of the article if you still have your copy of Mark’s Times. Part 1 is also available on Mark’s web page www.marksoutdoors.com). Just scroll down to near the bottom of the page and select “Hunting and Fishing Articles.” We next give an overview of my findings concerning the sonar cone angle coverage.

The previous article established that by using the pop-up feature of Lowrance’s Sonar Viewer program, I could easily establish the distance or range from the top of the arch (i.e., the depth of the fish) to the beginning and ending of the characteristic arch signal (when the fish first entered and left the coverage cone). Thus, by using a little trigonometry and choosing a representative sample, I had the ability to approximate the actual degree of cone coverage of a known size and species of fish.

An examination of my six fish sample produced an average cone coverage angle of 58.6 degrees for these water conditions for stripers weighing around twelve to fifteen pounds when centering the fish in the cones path. However, if fish are not centered in the sonar coverage cone a smaller arch for the same size fish size is drawn. Likewise, black bass, being a smaller fish, will display as smaller arches since their sonar return will be less. Because they are smaller the effective cone angle coverage will also be smaller. Some preliminary work on 14 inch spotted bass suggests perhaps twenty degrees.

In this second part we discuss how the trigonometry was applied to calculate the angle. Also, some of the Lowrance settings useful for Smith Lake for stripers are discussed. All of the units used have memory. That is, the unit remembers its settings even when the unit is turned off and on. Thus, you do not have to readjust settings once they are set.

Methodology
First, I selected the sample by looking for and choosing fish that produced a symmetrical arch as displayed on the sonar log playback. That is, the arch's beginning or leading edge and the ending or trailing edge was approximately equal. Secondly, I wanted an arch thick or deep in its middle. A strong or thick signal relative to the surrounding arches should indicate that the fish was likely to be centered in the cone’s range and thus directly under the transducer.

This shortest distance represents in trigonometric terms the adjacent side to the cone’s triangle when viewed from the side (i.e., in cross section). Additionally, the distance to the ending or long side, of the arch’s signal is the hypotenuse of a right or ninety degree triangle.

I could then divide the adjacent side (top of the arch) by the hypotenuse side (low point of the arch) and produce a cosine value. Looking up the value in a trigonometric table or, better yet for me, using a scientific calculator yields the angle. Then doubling or multiplying by two the angle produces a two-dimensional or side view of the actual total cone coverage angle.

As an example, one striper has a depth of 27.3 feet to the top of its arch and 42.2 to the origination of its leading edge. Remember, the leading edge and trailing edges are both approximately equal. Then dividing 27.3 by 31.7 is .861. The cosine of .861 is an angle of 30.6 degrees. Then, doubling 30.6 degrees produces the total angle of 61.2 degrees which includes the beginning and ending of the cone’s coverage when the fish was centered in the cone. Some features and settings used on Lowrance’s sonar/GPS units are discussed next.

Some Features and Setting Used Ping Speed controls the rate the transmitter and transducer broadcast sonar sound waves or pings into the water. When the ping speed is selected from the menu a Ping Speed control bar appears. Fifty percent is the default option (e.g., 10 pings/sec). I usually operate mine at seventy-percent or one-hundred percent (e.g., 15 pings/sec or 20 pings/sec). By bumping up the rate you can operated the boat at faster speeds without compressing the display and possibly missing something. This helps save time when searching for schools of shad or game fish. I adjust the speed down if I am around other boats and pick up some pings from their units. This interference will appear as vertical lines on the display. Using lower rates might also help when operating in shallow water to avoid confusing the unit’s microcomputer in some cases.

I like to keep the Surface Clarity and Noise Rejection filters adjusted as low as possible without excess clutter screen. By minimizing these filters, maximum target separation is obtained. This separation might be as small as one and one-half inches between objects. This can really help when fish lie close to the bottom. By using the Upper Limit feature and then selecting five feet, a lot of surface clutter is eliminated without increasing the Surface Clutter adjustment. Any fish shallower than five feet will spook or flee with a boat directly overhead in anyway.

Choosing and selecting a Lower Limit to the column of water I fish increases the number of pixels (picture elements) or the number of small block available to draw the arches. For example, if I choose an upper limit of say five feet and a lower limit of perhaps fifty-five feet and if I have a 480 pixel display then each pixel will represent 1.2 inches. If I left the unit on automatic depth and the actual depth was 155 feet, each pixel would represent 3.6 inches in the 150 foot band of water. Remember, there is lots of 150 feet water in Smith Lake. By maximizing the available pixels in the depth window of the selected water column my electronic pencil has a finer point and will display a crisper image on the screen.

I also adjust the sensitivity up as far as possible without producing too much background clutter. Maximum sensitivity gives the effect of as wide a cone coverage as possible.

Also, by Zooming and selecting the split screen option, two-times (2X) or twice as many pixels are available in the second window. A zoom power of four-times is also available but I use two-times most of the time. Zooming in expands the arches vertically and can aid in their interpretation as fish, a bait ball, bottom separation, etc.

I then usually center the zoomed window around twenty-five feet and add additional information using the Overlay Data feature to the screen. The data might include water temperature, water depth, compass direction, and boat speed from the GPS.

Closing
Remember that there is no substitute for time spent on the water time when scouting for schools of stripers. It can take hours of patient looking to find a school of fish such as the picture in the first installment of this article (www.marksoutdoors.com), which is Mark’s website. By the way, that diagonal line, going down from left to right, in the picture was a striper that struck a shad that one of Bill Vines (www.stripefishingheadquarters.com) clients was using as bait. That fish exploded out of the school of stripers about twenty-five feet down and stayed in the sonar’s coverage to about four-five feet. Note that the fish images are not nice symmetrical arches but rather irregular in form. This characteristic shape mean the fish are “hot” and are moving rapidly. This is one way to estimate what kind of fish you are viewing. These are fast movers as opposed to slow movers like carp or gar. The latter tend to be long, smooth, and flat. Once more, check with Michael Belcher at Mark’s for his Lowrance recommendations for your particular application or look us up at a boat show near you.