Hi Matt and everybody else!
I have a question about keel offset. I set a keel offset on my HDS unit and in RM. So, are they added when I use data to create maps in RM? For example, if I set keel offset on my HDS to 0.2m and in RM 0.3m, would it mean that my maps in RM are created as if transducer is 0.5m below see level?

Matt will have to correct me here, but as far as I remember the offset you enter in your HDS is not carried on to the sonarlog.

Thank you Team!
Does anybody else know this for sure?
Matt?

I can't confirm whether or not the Lowrance keel offset is already included in the depths that we take from the log files, but I can confirm that all the keel offset does in RM is add the specified depth to all points within the track. E.g. specifying a 0.2m offset will simply add 0.2m to every track-point depth.

Any ideas who I could ask?
Lowrance support?

Keel offset in the unit is only a screen setting, not fixed in the log. You can test it self on the water or with help of an exsting log, playing in the simulation mode and record again with a big keel offset. You will see the result. Conclusion: important is a right RM keel offset.

Thank you Fjordfisher!

Sounds like a simple thing but still, why wouldn't we set everything right :)

It's probably also worth noting that the "keel offset" in RM isn't what you would always consider a "keel offset" on other systems. RM adds the value of the offset to the depths, so really this value is a "transducer depth". The naming is a bit of a historical anomaly, but the action is (hopefully) clear when it is used. In many systems I believe the keel offset actually reduces the displayed depth by the offset amount - this is to show the amount of clear water underneath the keel (e.g. if you had a deep keel in a sailing vessel). I am not sure which way the Lowrance units do it.

Good remark Matt! Thanks!

Matt wrote:
You are correct, this is how Lowrance (and others) does it. "Keel offset" is more like "Safety depth".

No :-) (at least for Lowrance)

If you want depth below the keel, offset will be negative like -0.3
If you want depth below transducer, offset = 0
If you want waterdepth, offset will be distance waterlevel - transducer like +0.3

Agree, very confusing to use Keeloffset! Raymarine is using Offset and then options: • Waterline • Keel • Transducer (default)

The offset setting isn't related to the graph/screen only, but linked to the transducer. Also linked 'shared' by N2k and ethernet

I have 3 transducers, Airmar (linked with my Mercruiser engine), TM150 and SS 3D

Below are two for my N2k PGNs captured by my N2k recorder ( www.yachtd.com/ - Can be used with RM www.yachtd.com/news/#reefmaster )

Airmar



TM150 (See positive offset = waterdepth)



/Robert

Just did some test, to see how YDVR Converter v1.03 (Software for the recorder) is handling the offset:

N2k PGN:



GPX 1.1 (Note that a negative elevation is used)



Garmin V3 (Used for RM)



The output is the measured depth + (transducer - waterlevel) = water depth :-)