Lowrance Elite-7 - Increase Coverage Tip
2013 Aug 10
With the launch of the new Hybrid Dual Imaging (HDI) units by Lowrance, high frequency sonar has become very affordable. What Lowrance has done, is take their award winning Broadband Sonar (83/50/200kHz) to create clean fish arches, and combined it with their life like DownScan Imaging (455/800kHz) in a single transducer.
There is however a down side to the HDI, no SideScan. This dramatically reduces your coverage area when looking for structure and cover. For example, in order to see a screenshot like the one below, you would have had to pass the tree within less than 18ft. That means that you would have to run a grid of 16ft intervals in order to cover an area that is on average 20ft deep – that will take forever!
So what can you do to increase your coverage without forking out more than double what you just paid for your HDI system to add SideScan? It’s quite simple actually, by manually controlling the range. Just because the 455kHz has a beam of 47° left to right and less than 3° from fore to aft, it does not mean that it can’t ‘see’ further.
Auto range would typically select a range of 30ft when in 19 to 28ft of water, therefore limiting the soundwave to pretty much what is directly beneath the boat only, and that is what DownScan is supposed to do.
If you increase the range manually and turn auto off, you will start to see a lot more than what is directly beneath the boat. Take this screenshot below, that point of interest would not have been visible at all if on a range of 25ft, and even at 30ft you would have just caught the base of the standing timber making it impossible to identify as a point of interest.
The only problem with this tip is that you cannot simply extend the range as far as you want, like we do with SideScan until the power of the soundwave fades out. DownScan has very similar properties to conventional 2D sonar in that it has several echos, like when shouting into a gorge and you get the echo repeating itself but getting weaker each time. These second echoes are rarely seen when on auto because the range just simply isn’t large enough to show it. Unfortunately, it are these repeat echoes that will wipe out any information past the point where the next echo begins. So in order to select the correct range, you increase until you just start to see the second echo, and that becomes your new ‘virtual’ bottom. In this screenshot here, I should have been at a range of 50ft, not 80ft. This would have allocated a lot more pixels to my point of interest making it that much easier to identify.
You can now create a waypoint of this POI, but we have no idea if it is to the left or right of the boat. We therefore need to know the position of two axis, X and Y. Once you spot something like this, you immediately create the first waypoint establishing the X axis.
The next step is to make a very wide turn to either left or right and approach your first pass trail from right angles heading straight for the waypoint.
When you spot the POI, you create your second waypoint, thus creating the exact spot on both axis. Don’t forget to delete the first waypoint now so you don’t target the wrong one when you come back another day.