In the case of the 8 degree Lowrance transducer,  proper position for good readings at speed meant lowering it quite a bit into the water. As noted earlier, this produced a noticeable roostertail, which sprayed water onto the top of the motor hood. On the other hand, the 20 degree Lowrance tranducer did not produce a roostertail, and gave good performance down to 240 feet. The 8 degree transducer did work as promised, giving reliable readings down into the 400 - 500 foot range.

A call to Lowrance Technical Support confirmed that if the X-85 could not obtain a bottom lock, it would not function properly in the automatic mode. In order to mark anything when this happened, the unit had to be set to manual mode, and the depth range and gain (sensitivity) adjusted manually.

Once this was done, the unit worked well, but adjusting gain manually was a major effort due to the user interface. And adjusting gain in manual mode had to be done quite frequently. When running the boat, we had to turn down the gain or increase noise suppression to avoid a black screen from boat noise. Once stopped, we had to turn the sensitivity back up in order to mark fish.

The LS-6100 did not have this problem. Switching to manual range mode did not affect the automatic gain and noise reduction functions. In any event, even if this was required, the LS-6100 user interface made it much easier to adjust gain and range.

Another feature the Furuno unit had which seemed to help deep water performance is something call "Time Varied Gain" (TVG) or "Deep Gain".This feature increases the gain for echoes returning from far away. This allows echoes in deep water to show up on the screen with comparable intensity to echoes higher up in the water column. Deep Gain worked well, allowing us to get good fish echoes at depths well past the 240 foot mark.

As mentioned earlier, the LS-6100's speedometer also had issues. We could calibrate it to match our GPS speeds within certain ranges (say 0 - 10 mph, or 20 - 30 mph), but it never matched the GPS over the complete range of boat speeds. In contrast, the Lowrance speedometer tracked the GPS over the complete speed range of the boat (0 - 30 mph) without any additional calibration.

Depth Range:

We originally thought that having a very large depth range was important in offshore fishing. We've now come to the conclusion that for us, it's not that big a deal. Once we get well offshore, we typically set the depth range to 200' on 200 kHz, and leave it there. The 200 kHz signal produces a clean return, and good definition in the depth zone we are most likely to raise fish from.

50 kHz or Not?:

There is one school of thought that the 50 kHz signal should be used offshore because of it's much wider beam angle (typically 45 degrees), which lets you see further out to either side of the boat. In practice, we've found that on Toy Boat 2 the 50 kHz signal is affected too much by noise to be very useful while trolling or running fast (this may be an issue primarily with small boats). It is most usable when moving the boat slowly or drifting.

How Many Watts?:

Along the same lines as maximum range, there is a question of how many output watts are needed in an offshore sonar. Clearly, more output watts means more depth. However, a side effect is that it also improves sonar performance when running the boat.

This phenomenon can be likened to driving around in your car with the radio tuned to an AM station and the windows open. If you're going down the freeway, you need to crank up the volume in order to hear anything. If you're listening to a powerful radio station, the signal is very strong and you can still hear the music. If the radio station signal is weak, turning up the volume also makes any background static louder as well, and you can't hear the music very well.

So more watts seems to make sense from the standpoint of getting clear echoes under all conditions. However, there is some body of evidence that even though sonar makers claim fish can't hear the sonar pings, that fish actually can feel or hear them at some level, and heavily pressured fish are turned off by them. So more watts in that case actually works against you. Something to think about, anyway...

• The most useful mode of sonar operation for us has been 200 kHz, with automatic sensitivity and noise suppression, and a manual lower range set at 200' or so. Under these conditions, even sonars with 300 watts RMS of power can produce clean echoes when running at moderate speeds, if the transducer is properly installed.
  
  
• Maximum depth range on the sonar has not been a major issue offshore because of our 200' cutoff. We have made use of the deeper ranges when we are bottom fishing, but not while fishing for tuna or other gamefish.
  
  
• 50 kHz operation has been of little value to us so far, primarily because it is more heavily affected by noise.
  
  
• More watts can help produce better sonar readings when running the boat, but there could be negative impacts on sound-sensitive fish.
  
  
• All sonars are not alike. Some work better in shallow water automatic modes, some work better in offshore situations. Key features to look at for offshore small boat use would be:
  
  
  • Ability to operate with automatic sensitivity and noise suppression with no bottom lock and a manual range set
    
    
  • Time-Varied or Deep Gain feature
    
    
  • A good user interface