Garmin Keel Offset

[rpmerrill]

I've been getting acquainted with my Garmin and came to the Keel Offset page.

I know my draft is ~25 inches, but I don't know where my depth transducer is located.
I've been snooping around but haven't seen anything that looks like it should be a depth transducer.
What should I use for an offset? Probably something less than 2 ft...?

Thanks

 

[Pilotnavigator]

Best process is to put the boat in shallow water and measure the depth of the water and compare to your plotter reading. Use a line and weight. Now figure out if you want the plotter to show actual depth or depth under keel. For depth under keel you will need the measure of keel to water line along with the actual depth and the reading of the plotter calculate want to offset will be.

 

[sleepyboat]

Go to the Ranger Factory Technical Bulletins.
R 27 Owners Manual.
Page 9 shows the transducer mounted internally on the starboard side above the lowest chine. Which puts it on the top quarter of the prop.
I put my off set at 2 ft to give plenty of warning on my 27.

 

[rpmerrill]

Aha, thanks a lot. Duh, it was right in front of me.
My offset was set at 2-1/2 and at low tide in my slip I was getting negative numbers.
As I recall, the prop is 18" dia, so 2 ft is conservative and 1-1/2 ft even looks ok.

Thanks a bunch!

 

[sleepyboat]

oh ya, the alarm goes off all the time while i'm up river. it keeps you on your toes.

 

[chronicity]

Aha, thanks a lot. Duh, it was right in front of me.
My offset was set at 2-1/2 and at low tide in my slip I was getting negative numbers.
As I recall, the prop is 18" dia, so 2 ft is conservative and 1-1/2 ft even looks ok.

I'm trying to make sure i have this right. At 1-1/2, that will give you the depth from the bottom of your keel (skeg, in my case) to the seabed, under the assumption that the bottom of your keel is 1-1/2 feet below the sensor (which itself is below the waterline). If you want to see actual water depth, you enter - 2, (that is, negative 2) where 2 is the actual depth of your sensor below the waterline. Hypothetical numbers. I dont know the depth of the sensor on my R27OB.

 

[knotflying]

Everyone has their preference just as long as you remember what the number on your screen is telling you. I prefer water depth since this is what the charts give you. This is also the easiest to calculate. As mentioned above go into shallow water and drop a line with a sinker to the bottom. Pull it out and measure the length. Now go to your offset page and adjust that number so that you get the same depth on the screen as the length of your line. On my R-27 I draw about 26 inches. I set my depth alarm at 4 feet. That will give me about 2 feet below the keel. Keep in mind that I do most of my cruising on the east coast and towards the south so the bottom is sandy. I know you guys in PNW would totally panic at four feet. So use an alarm depth that makes you feel comfortable.