Anchor watch alarm

[Clyde_Wanderer]

If your plotters distance measurements are set in nm what decimal point/s of a nm would you set your anchor watch alarm to? or would you reset the distances to metres for the duration you are using the alarm and reset to nm when you have left the anchorage?
C_W

[Alan_D]

I usually set mine to 0.02 Miles, unless I remember to set it before I have fallen back on the anchor, in which case 0.01Miles.

Alan

[Silkie]

The anchor alarm on my gps is set to feet and I generally set it between 60 and 100 i.e. 0.01nm and 0.017nm respectively.

[Clyde_Wanderer]

Thanks for that guys, my alarm only has 0,00nm, has yours got 3 zero's after the decimal point Silkie?
I think 100 feet would be a good figure.
I would assume one would want to take the length of boat and add the length of chain out plus a few feet for good measure, would I be correct?

[Alan_D]

It depends where your starting point is. If your alarm is centred on the point at which you dropped anchor then your calculation is about right. If you wait until you have fallen back on your anchor to set your starting point you need to double the number you first thought of. If the tide and/or wind move through 180 degrees you will be able to travel that distance without dragging your anchor.

Alan

[Clyde_Wanderer]

It depends where your starting point is. If your alarm is centred on the point at which you dropped anchor then your calculation is about right. If you wait until you have fallen back on your anchor to set your starting point you need to double the number you first thought of. If the tide and/or wind move through 180 degrees you will be able to travel that distance without dragging your anchor.

Alan

I understand what you are saying Alan, but would the starting point not be the distance the antenna is away from the point where the hook was dropped plus the length of rode out and a bit of margin, then everything doubled to cater for a 180degree swing?
C-W

[Alan_D]

Yes, that would then be the diameter of the swinging circle. If one were smart/well-organised one could activate the alarm as the anchor is dropped and then the alarm could be set for the radius of the swinging circle, i.e. half as much.
The drawback of using the diameter is that if you drag with the wind/tide still acting in the same direction you will have gone quite a long way before the alarm goes off.

I think with some plotters you can set the alarm starting point using the cursor.

Alan

[Shuggy]

I set mine to 0.03nm. It's only gone off twice at this setting; once when we were dragging (the only time we've ever dragged, touch wood) in West Loch Tarbert, Jura - heading East at about 5 knots, the other time when we were in Loch Craignish and the wind got stronger and stronger and I had anchored with 25m of chain which was let out to 60m at 2.30am. The alarm went off about an hour later but I didn't hear a thing. Scared my wife, though! False alarm caused by increased scope.