Some Thoughts on Offshore Sonar Use:

Sonar Reflections

A good sonar unit may not be essential when fishing offshore, but it sure helps! This article covers some of the more subtle points on sonar selection and use that we encountered while setting up Toy Boat 2...

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Background

Comparison

Install&Setup

User Interface

Performance & Next Steps

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Like the cliche about art ("I don't know anything about art, but I know what I like"), "usability" is a hard thing to define. People who design equipment are faced with a significant problem: creating a simple way to control the equipment, while still giving people who need precise control a way to do it.

As you might expect, we found the X-85 and LS-6100 user interfaces to be very different. The X-85 interface, in our opinion, is designed for people who will not be adjusting the unit much while fishing. The LS-6100 interface is oriented towards people who need quick access to more technical features.

It's not that you can't get to the technical settings on the X-85, it was just a much more tedious process.

For example, in offshore use, where the bottom may be 2000' away, it is quite common on any sonar to set the depth range manually to something fairly shallow (say 200'), and adjust the gain manually as well. In fact, on the X-85, we found that this was mandatory in order for the unit to operate correctly offshore. This would imply that a quick way to manually adjust range and gain would be important. Similarily, if you run at night, being able to easily dim the display to preserve night vision is important.

Unfortunately, getting into manual mode and adjusting depth and gain on the X-85 required a fair amount of button-pushing and menu-diving, as did adjusting display brightness and contrast. By comparison, accessing these items on the LS-6100 was a piece of cake. Typically, one or two pushes of a button were all that was required to reach the desired menus.

Another interesting area was the treatment of gray scale on the display. When a manufacturer says that something will be "gray" on a black-and-white screen, what does that mean to you?

To us it means varying degrees of darkness in each of the pixels dots) in a shaded area. This is how the LS-6100 handles gray.

However, another way to display gray on a black-and-white screen is to mix a varying number of light and black dots. For a lighter shade of gray, add in more light dots. This is similar to how your printer creates shades of gray. This is how the X-85 handled gray.

On monochrome sonar units, the presence of gray in an echo implies a "harder" return. This is usually a result of density differences between the object returning the echo and the water. The more difference, the more gray. Fish with air bladders (like baitfish, bass, etc.) can return echoes with gray in them. Fish without air bladders, like tuna, give weaker, less contrasty, returns.

So why is the method of rendering gray on the screen important? If you have a 200 foot range on the sonar, and your screen measures 200 pixels high, each dot represents 1 foot. If your fish is a foot high, the echo may only be one or two pixels thick. If the grey scale is created by alternating light and dark pixels, versus making the pixels lighter or darker, it can be very difficult to see the differences in the mark.

courtesy Lowrance
Electronics

"In the Good Old Days..." the Lowrance flasher sonar display was the hot ticket. Flasher sonars had a round display like a clock, with depth markers around the face. A red light was mounted on the end of a rotating arm that spun inside the dial. As the arm spun around, the light would flash at the appropriate time to give a mark at the right depth. The brightest, deepest flash was the bottom, flashes above the bottom were echoes of some sort, sometimes fish, sometime bottom structure.

Many people initially thought sonar graphs were going to be far superior to flashers, but it soon became obvious that graphs suffer from one major flaw - it takes a certain amount of time for the display to scroll far enough for the angler to be able to see an echo. By that time, you might be well past the target.

For that reason, Lowrance, Furuno and others added a "real-time display" feature to their sonar graphs. Basically, these real-time displays are the flasher unit display straightened out into a vertical bar on the right side of the screen. They show real-time echo blips just like the flasher, only they take the form of horizontal bars at different depths..

On the old X-85, these bars are all displayed with the same width but varying intensity. On the LS-6100, the width and intensity of the echo bars vary according to echo strength. Strong echos are wider and darker than weak echos.

LS-6100 A-scope
courtesy Furuno

Furuno products, as well as most other sonar manufacturers, call the real-time feature with signal strength indicator "A-Scope". Lowrance called the X-85 feature "Fastrak". Sometime after the X-85, Lowrance added the varying-width signal strength indicator to Fastrak, so it is functionally equivalent to A-Scope.

Why are A-Scope and Fastrak important? The ability to instantly see and judge the strength of an echo is a very useful tool for distinguishing fish and seperating out noise / trash - much better than using the graph alone.

X-85 (left) and X-125 (right) FasTrak
courtesy Lowrance Electronics

When an echo is displayed on a monochrome graph like the LS-6100, the intensity of the echo is shown as one of 4 shades of gray - essentially rounding the echo to one of four levels. With A-Scope, the signal intensity is shown as the width the horizontal line - wider lines are stronger echoes. The width of the line varies continuously, rather than being restricted to 4 levels. This permits a quick, accurate assessment of echo strength.

For example, we've found that many of the small blobs that appear on the sonar when running the boat at speed are not small bait schools as we originally thought. They are actually the result of noise coming from the hull slapping the water as we run. With A-Scope turned on, it was obvious - we would hit a bit of chop, and immediately see a weak echo appear on the A-Scope, which then turned into a small blob on the graph. By having A-Scope running we could immediately correlate the echoes to the impact of hitting the chop.

courtesy Furuno

courtesy Lowrance
Electronics

Both sonar units have temperature displays. The LS-6100 overlays the temperature display on top of the sonar display. This gives a more accurate linkage between the temperature and the sonar reading, but can be very difficult to see the temperature trace when there is a lot of stuff in the water. So difficult that we stopped using the temperature graph on the LS-6100. By comparison, the X-85 has the temperature graph in a separate window, which we preferred.

Another difference between the units had to do with the temperature limits that could be set for the graphs. We are often looking for small temperature breaks (0.5 degrees or so). In order to detect these small breaks, it is an advantage to be able to make the temperature graph show a very narrow range, so that small breaks are more obvious. For example a 0.5 degree break is much easier to see when the temperature graph shows a range of 2 degrees, than when the graph shows 10 degrees.

The temperature range on the X-85 could be set to much narrower ranges (2, 4 or 10 degrees) than the LS-6100 (16 or 40 degrees), which made it much easier to spot small temperature breaks on the X-85.

There are a large number of display technologies around. We won't even try to discuss them, because the bottom line is that the specific technology is not as important as how the screen looks to you under your fishing conditions. The key problems or issues that you need to consider are:

• Visibility with polarized sunglasses on
  
  
• Whether or not the screen remains visible when the display get hot( believe it or not, there are a couple of technologies which go black when the screen gets too hot from the sun!)
  
  
• Visibility from the side, and above
  
  
• Whether or not brightness and contrast are sufficient to keep the screen readable under bright sunlight. This is a particularly bad problem with some color sonars.

While transducer installation can make or break the performance of a sonar unit, the user interface will determine just how effective you will be while using it. This section was not intended to be a bash on any particular brand or model. As mentioned earlier, the technology is moving so fast that the technical specifics are dated. But here are the lessons we've learned:

• You need to put your hands on a sonar unit before you buy it:
  
  
  • Go to a store that has working demo units, or a trade show, and go through a typical trip. Be sure to bring your polarized sunglasses!
    
    
  • Try the moves you would typically make with the sonar, and decide if the interface is too clumsy for you to use. Keep in mind things like manual overrides for range, gain (sensitivity), noise reduction, screen brightness/contrast.
    
    FYI, Lowrance has emulator programs available for some of their products. You can download these demos (click HERE to see the download page for the X-125 emulator), and try out the controls and menus on your PC. Very slick...
    
    
  • Look at the display and see if you are satisfied with the way grayscale or color are handled, and where things like temperature graphs are located. Also check for visibility with polarized sunglasses, from the sides, above. Check contrast and brightness.
    
    
• If you haven't already, check out A-Scope / Fastrak