GPS Anchor Drag Alarm

[denpooch]

Hi folks, I would like to tap into your expertise regarding an anchor alarm.
I am getting a new Chartplotter this season and am interested in using the 'anchor drag alarm' feature.
The Garmin instructions state that when enabling the alarm: "...Select Set Radius, and select a distance on the chart."
Can anyone let me know what 'formula' you use? For instance, if I am in 10 ft or water and have let out 40 ft of chain (about 3.5:1), do I set for a 40 ft radius? Do I allow for a 360 degree spin, while assuming the anchor stays in one place?
That seems the logical setting but I would appreciate your advise.
Thanks.

[Midnightsun]

Set it so you have some room to spare. If you are in 10ft of water then a 40' radius allows for some play but not all that much. Personally I would add an additional 10' to the 40' setting the alarm at a 50' radius. Nothing worse than being disturbed in the middle of the night from a false alarm.

[bud37]

To add to Hans....these boats as I am sure you already have noticed hunt around a lot at anchor ( got one )....so any settings would have to have some room , also go out and set the alarm during a windy day and see what settings will give you alarms.I always want to know if there is a 180 reversal in wind direction no matter what.......

[Viper]

Is it monitoring by gps coordinates or depth? There's a difference and it depends on the anchorage you're talking about. If I'm anchored in 4ft of water, I want the alarm to be triggered by a change in depth (shallow alarm) not a gps coordinate. GPS isn't accurate enough to react to a difference of only a few feet. At that depth, a little movement the wrong way can put you on bottom, again depending on the anchorage. It's okay for the opposite direction where you might be dragging away from an anchorage into open water, or set the deep water alarm.

[denpooch]

Thanks for the insights. All of your comments are very helpful and have given me some basic foundations from which to work.

[amanphoto]

There is a great app for your smart phone called "drag queen". Check it out. It will alarm you if you boat moves out of the designated area.