T&T: Anchor alarms and chart plotters

[Wray West]

>  A feature I wish chartplotters had was an anchor alarm position 
> setting feature, whereby I could say the anchor was
>"x" feet in front of the boat.

Although it is not an "alarm", I have at least come up with a method 
to place a dragging indicator on the chart plotter.

As I am coming into an anchorage, I create a mark on the chart at the 
location I think looks like a good spot.  I set 5 range rings and set 
the distance of each ring to the depth + tide + distance to bow 
roller.  This gives me a mark I can move around as I am thinking 
about where I may drop anchor to see how the boat will move around as 
wind and current shifts with a 5:1 scope.

After I have put the anchor down, and I'm backing down, I move the 
mark to where I placed the anchor.  I can tell this on the chart 
because this is where my track suddenly changes to my back down 
direction.  I also adjust the distance between rings for the final 
depth.  As I let out the scope, I expect to be all out as I reach the 
fifth ring (I have a chain counter to tell me how much is out).  If 
not, something is wrong, usually the anchor is having trouble 
setting.  Once set, the boat track on the chart follows a track 
around the arc of the fifth ring.  If the wind or current shifts, 
there may be a track across the inside of the circles, followed by an 
arced set of tracks on a different edge of the circle.

If the track ever gets outside of the circle, I have 
dragged.  Usually the drag and reset is obvious in the tracks on the 
plotter.  I watch this carefully after setting the anchor and find it 
gives me a pretty accurate picture of whether I have a good hold.

Now if the chart plotter companies would let me enable an alarm if I 
left the circle, I'd be all set with a great drag alarm

Wray West
M/V Anjumal (Cape Horn 65)
Portsmouth, NH
www.anjumal.com