First, thank you MarkSF for the manual. Now give me a second for the vertigo to end...
The manual covers the 200 series products, not the 800 series that we have been discussing, but it seems likely that they have the same or similar firmware. The 2010 date would indicate that it is current
thinking at Airmar. Of course it is marked "Proprietary and Confidential" for a reason - it is certainly not info for the novice
. The info of interest is located in Airmar proprietary PGNs protected by access level control. We probably shouldn't be doing this, so let's slog ahead.
The calibration for the depth sounder is for the Speed of Sound in water
used to calculate the depth. The speed differs based on salinity and I suspect this is for correcting salt water
vs. fresh water
. There is no keel
offset function that I can find in the document, so for the depth info I will return to my earlier statement: keel
offset must be done in the MFD.
The speed calibration described is a piece-wise linear calibration. While it is possible to manually calibrate the knotmeter
using these PGNs and a computer and N2K bridge, it would be preferable to use purpose-built software if one could find it. There is a PGN for gathering the raw data (pulses/sec) that could be used to collect the pulse rate for each GPS
speed, then graphed and fit with the appropriate piece-wise linear "curve". This is pretty cool, but not something that many users could do manually. Press ahead if you like - it would make me a bit nervous though. The typical user calibration is simply a multiplier, and again I have to conclude that this should be in the MFD.
There is a simple temperature offset available as well.
I checked out the Lowrance manual and agree that the only calibrations are found by selecting the device list. Have you tried to calibrate depth? I would be interested in knowing if that calibration is an offset in the MFD or the speed-of-sound in the sensor. I am not surprised that Lowrance is not supporting the sensor's proprietary calibration, but they should have offered a scaling correction. I find it a little hard to get excited by an offset for the temperature, but what the h... Lowrance seems to be coming up short.
What is interesting is that the Simrad
MFDs do have depth and temperature offsets as well as a speed calibration (which appears to be a multiplier). Simrad
is in the same Navico
portfolio as Lowrance; the difference is that Simrad tailors their products for ocean sailors and Lowrance for fishermen. Along these lines my old Lowrance digital depth sounder lacked keel offset, to my continued annoyance. Apparently not needed for fishing
I just checked and my Furuno
NN3D does have keel offset, speed correction, and temperature offset.
If I were in your shoes I guess I would either return the Lowrance if possible, and maybe get a Simrad unit. Or work out how to calibrate the sensor directly. Otherwise the lack of calibration would drive me crazy(ier).