Anchor Dragging? | Sailing Blog - Technical Hints and Tips - Sailing Television

Anchor Dragging?

One of the great pleasures of the cruising life is settling down in a lovely anchorage to watch the sun set. Your boat is your own little island!
Hopefully your anchor is well set and will hold even if the wind in the night gets up a bit, or shifts and you swing around...

This often means I am up in the night checking all is well and we are where we are supposed to be. Check bearings on other nearby boats, check the beach astern hasn’t come any closer....

For many years I have been using a small handheld GPS beside the bunk to make a plot of where we have swung., After a few hours it shows an arc of dots indicating we are (hopefully) where we should be. But this means I have to wake up and check the plot. I haven’t been able to find a good anchor alarm. The ones I have seen are all add-ons to a GPS - not a purpose built system. They all seem to require me to set the alarm while we are anchoring otherwise the centre of the alarm circle is where we pushed the button - not where the anchor is on the bottom. I have always hoped for an anchoring alarm designed just for that purpose - where you can set the centre of the circle where your anchor is, and plot the anchor position.

Anchor Alert - SEE UPDATE July 2014

This is an iPhone App that does just that... I had a chance to test it as we anchored in the remote Cala San Pedro on Spains coast a few days ago. You can set the spread of yellow dots showing where we have drifted within the red circle I have set as a safe radius. The centre dot is our anchor. Drift shows we are currently 18 meters from the anchor. This was done with the iPhone down in the cabin - try it on your own boat to see if the smartphone has a sufficiently sensitive GPS to receive belowdecks.

To set the Anchor Alert with an "offset" is quite straight forward although I had trouble at first since it isn’t in the manual. I emailed the developer (from our anchorage!!) and he kindly sent me directions.

1) Press the "lock" icon in the upper right of the screen
2) Point the phone to where the anchor is.
3) Drag the boat back until the position on screen reflects your current position back from the anchor in real life
4) Press the Set button (currently showing "clear" in the lower left) and choose "Offset"
5) Press the lock icon again.

I set the alarm and it didn’t give any false alarms during the night - nicely plotting the yellow dots. The blue circle is the GPS uncertainly of our actual position (shown in the top menu GPS accuracy). A fancy feature is the overlay of a Google Earth Satellite photo if your phone is on the internet to download it.

If you have an iPhone I recommend this App - for the mere fee of $3.99 (Check Here for Update July 2014)


If you use Android you also have an App, and its also called Anchor Alert, although it has nothing to do with the iPhone one!! It looks even better as it has an exclusion zone option so you can set an area of the circle you want to remove from your safe-zone. This would be useful and would alert you if the wind switched and you wanted to wake up to check if the anchor was safely reset. Its 12Euros. Also looks like excellent value. Anyone out there with an Android phone who has tried it?
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