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Thread: Garmin GPS and the Anchor alarm

  1. #1

    Default Garmin GPS and the Anchor alarm

    I've got a question for those who use their Anchor Alarm on a regular basis. From the Garmin users manual for my gps I cannot determine from what point the alarm is set. For example do you mark the spot just as you drop the anchor and that becomes the center point of the radius or what? I've experimented with this a bit and so far I can't say for sure how this works. Any body with the answer??

  2. #2
    Member jrogers's Avatar
    Join Date
    Apr 2006


    Yes, generally the place where you drop your anchor. That is, unless you drag it a bit until it sets. Ideally you set it rigjt over top of where your anchor ends up getting set at because it is a radius from a set point and you can swing around the anchor with winds and tides. To be honest, I just usually set bigger radius instead of trying to get back over the anchor once it is set.

    As a related question, how many of you use the depth alarm as well? Mine seems to error at times and cause alarms so I really don't use it. I think it may be things like seaweed or jellyfish. Do others have this problem?
    2009 Seawolf 31'
    Fully Loaded

  3. #3


    Yes I've had problems with the depth alarm, I also figured it was sea weed or something in the water. I've also had problems with the anchor alarm. I can see the swing track and for no reason I see a straigt line to a point and than right back to the swing path. I wonder if this is caused by the unit switching between satelites?

    So you must set your point as your dropping your anchor?? I always seem to forget this.

  4. #4

    Default Anchor Alarm & Scope Ratio's

    Your right I thing the depth alarm get to many hits on jelly fish and seaweed to work well. I set for 2' but it's not fool proof, thought some day I'd rig a line with a bell or? to give me the hint.

    Example 20 foot of water where anchor is at=
    1/2 radius Radius
    scope rode length swing area alarm set
    Optimun Anchor design scope 7:1 140' 280' 300'
    4:1 80' 160' 180'
    pratical 3:1 60' 120' 140'
    2:1 40' 80' 100'
    Lower scope needs more or heavy chain to keep the anchor head down so it can keep a bite. I always raise my motors, try to anchor where I can see bottom first or know it, so if I do go dry there are no rocks to sit on.
    I have too, and in 20 years have had no issues, but always try for 4:1 !

  5. #5

    Default Didn' Post like I layed it out

    first is Scope ratio,
    2nd is rode length,
    3rd complete swing area
    Alarm set @

  6. #6


    When I drop anchor, I set a waypoint to show where the anchor is. Then I back up as I let out the rode and tie it off and set the anchor. Then I use the cursor on the chartplotter to measure the distance from where I am to where the anchor is. Then I double that distance plus add maybe a little more. So if when I set the anchor I'm 100 feet from the anchor, I'll set the alarm for maybe 220 feet. That way if I can swing all the way to the other side of the anchor (100 feet on the other side), that's 200 feet, and the alarm shouldn't go off. If I forget to set a waypoint where the anchor is, after swinging on anchor for a while and seeing the arcs of breadcrumb trails, then I can figure out about where the anchor is.

  7. #7
    Member breausaw's Avatar
    Join Date
    Oct 2006


    Seems everyone has their method.
    Essentially, after setting the anchor I look at my track-from this you can usually see where you dropped the anchor. I then take the cursor and measure from this point over to the closest obstruction/s, I then set my anchor drag alarm giving myself a comfortable fudge factor. Then I look at the tides and try and figure out minimum depth. If Iím in 40 to 50ft of water at high tide and it will drop 10ft to low I set my minimum depth alarm for example to around 25. I usually donít set the maximum depth alarm unless Iím worried about dragging out to deep water, but it thatís the case the GPS drag alarm would sound so I usually give myself a lot of leeway.

    It all sound confusing, but whatís important is just figuring out where you donít want to be and setting your alarms to prevent that from happening. Iíve been woken up in the middle of the night many times to false alarms, but not alwaysÖ.the alarms has saved my bacon a few times.
    07 C-Dory 25 Cruiser

  8. #8
    Join Date
    Apr 2006
    Anchorage and Seward


    I have a Garmin too. Is there a way to turn off the screen while on anchor/depth watch to reduce battery drain? It would be nice with the limited battery capacity I have. I had a separate digital sounder on my old boat I used just for depth alarm while anchoring out which worked well (other than the fish/otters/others swimming below waking me up).

  9. #9


    You should be able to turn the screen brightness way down which will make a difference on power usage.


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