gps keel offset

[ken52]

I have a garmin 188c gps/chartplotter. After setting it up I noticed that the skeg sits about 19" below the triducer. While reading the manual I can across the subject of keel offset. So I set my offset to +1.5'. Am I correct in doing this and does this now tell me that my unit is reading the depth from the bottom of the skeg and not the triducer? New at this stuff and boating. Any help/advise is greatly appreciated.

 

[bolo78910]

Re: gps keel offset

bump this up i want to kno too.

 

[dingbat]

Re: gps keel offset

The keel offset is just that. It subtracts or adds that number from the depth it's calculated with data coming from the transducer.

I'm not sure about your 188 but on my 4208 if you wanted to know the depth from your skeg you would have to subtract 1.5' (-1.5) not add it.

 

[ken52]

Re: gps keel offset

Thanks dingbat, I need to make sure I set this correct. I don't need to be off by a 1.5' down here, the waters in the gulf can get shallow fast.

 

[ken52]

Re: gps keel offset

I know this was an old post but for those interested this is what I found. Yesterday while out I decided to drop anchor and swim a bit. Looking at gps it was like 3-4' but when I got in the water it wasn't nearly that deep. My gps was set to -1.5', so I changed it to +1.5'. Now I really have a more accurate depth from my skeg to the bottom. Hope this my help.

 

[JB]

Re: gps keel offset

Readers need to understand that all this talk about GPS has nothing to do with GPS.

The topic is about SONAR.

 

[dingbat]

Re: gps keel offset

Readers need to understand that all this talk about GPS has nothing to do with GPS.

The topic is about SONAR.

Not necessarily.
Any Garmin chartplotter that supports auto-routing will require a keel and overhead offset value. Nothing to do with sonar. Calculates routes using 3D navigational charts.

 

[JB]

Re: gps keel offset

Not necessarily.
Any Garmin chartplotter that supports auto-routing will require a keel and overhead offset value. Nothing to do with sonar. Calculates routes using 3D navigational charts.

So it has nothing to do with SONAR?? Please explain just how the offset is used by GPS without SONAR.

 

[dingbat]

Re: gps keel offset

So it has nothing to do with SONAR?? Please explain just how the offset is used by GPS without SONAR.

Most of the newer Garmin Chartplotters /GPS have an auto-routing function when using the optional BlueChart g2 Vision charts.

The Vision charts are 3 dimensional charts. The depth and clearance data is incorporated into the charts. All you do is enter a "safe depth" and a "safe height" and the unit calculates the best route using the data in the charts.

 

[JB]

Re: gps keel offset

Now that is danged scary with real depth in many hazardous places varying by as much as several feet!! That includes, by the way, LOTW, where the rocks may be 6' down one year and 6" down the next.

Don't think I would trust last year's depths to this year's course.

 

[ken52]

Re: gps keel offset

Thanks guys, but wasn't trying to start anything here was just trying to help others. I guess the proper heading should have been adjusting keel offset on garmin unit.

Just thought a boater would have a more realistic depth in relation to their skeg and not the depth to ducer.