To make the most accurate and user-friendly Insight Genesis maps, make sure your GPS receiver is aligned properly with your transducer. If your transducer is transom-mounted and your Lowrance unit is console-mounted or bow-mounted, your mapping results won’t be as accurate as they could be. To make the best custom contour maps possible, install a thru-hull transducer below your console, or install a stand-alone GPS antenna “puck” in the stern of your boat, above your transom-mounted transducer.
Your boat’s GPS receiver is built into your Lowrance unit. Mounting your unit at the console and connecting to a transom-mount transducer creates a gap of five feet or more between your GPS position and the portion of the water column that your transducer is sounding (and displaying a representation of on your screen). This can be especially problematic when mapping an area with up-and-back/shore-to-shore horizontal passes, as such a set-up can cause the location of mapped depths to be five feet off (or more) in one direction and another five feet off (or more) in the other direction.
A tell-tale sign that your transducer is located too far from your boat’s GPS source is “crinkly” looking contour lines on your map (see yellow circle in Figure 3).
 |
| Figure 3. Result of a misaligned GPS. In this instance, the surveyor was using the GPS position from the internal antenna in a console-mounted Lowrance HDS unit located 7 feet away from a transom-mounted transducer. This positional bias was doubled as a result of the back and forth transect passes (the red lines). |
What to do?
If your boat doesn’t set up well to accomodate a thru-hull transduder under the console, consider mounting an external GPS antenna above your transom-mounted transducer.
The best option is Lowrance’s Point-1 GPS (Figure 4, at left). This low-cost solution will suit most Insight Genesis users’ needs. Although the published horizontal accuracy is 5 m, users can expect much better than this, especially in open water. If you require more rigorous horizontal positional standards, you can opt for a Simrad MX521B Smart DGPS antenna (Figure 4, at right) or a Simrad HS60 GPS Compass. Lowrance and Simrad also support any NMEA 0183 or 2000 compatible third-party GPS receivers.
Anglers will also be pleased to know that Point 1 antennas can help with your fishing as well as your Insight Genesis mapping. Check out this article by our friends at Wired2Fish.
 |
| Figure 4. Insight Genesis users can align their GPS position with their depth soundings by using an external GPS antenna. A Point-1 GPS (left) is the lowest-cost and most popular option. A Simrad MX521B (right) ensures higher reliability of submeter GPS accuracy with its capability of differential correction. |
C-MAP Fishing 
Thank you for the nice report. I too have these same wavy contours. I followed the installation instructions with my Point-1 and mounted it in their preferred location (in front of the helm’s windshield). No where in the Lowrance Elite Ti install manual did I see mention of aligning my GPS to my transducer. I even read several Lowrance help FAQ about making the best maps, they too did not mention this issue. Now I have to drill more holes into my boat to mount the Point-1 in a new location above the transducer.
Another simple solution to easily fix this wavy contour would be having Insight Genesis (or the plotter itself, allow me to input the distance between the GPS antenna and the transducer (like other mapping software does). This way the software can easily offset the readings and the problem can be removed. This would also retroactively fix all of the existing maps I have made. I have 30 hours this year alone just to do shore to shore, tight 50 foot passes across and down my favorite lakes.