So you think you might be dragging.....?

[Rich Stidger]

We have all had the panic when coming topside in the morning to see everybody in a different relationship to one another. Sometimes we are very close to another boat that was much further away the night before. So the immediate question- Did I drag?

If you have a chartplotter and if you have left it on since you anchored, you can look at the screen and see a plot of where you have been. If you see a circle or an arc then it is a pretty good indication that you have not dragged. That doesn't address why you are uncomfortably close to another boat, but at least you know you are still set in the same spot.
But what if the chartplotter doesn't show a nice circle or an arc? What if the winds were light for a while and you kind of drifted around? Now you have a chartplotter image that is not necessarily clear.

Well, as they say, "I have an app for that".
Here is a chartplotter image-

After anchoring I was on the large arc (to the NE) and the next morning I was on the short arc (to the SW). And during the night I was dancing in the middle. But, did my anchor move? This plot is not all that difficult to analyze, but I have seen others that are not clear at all. So I made a visual tool to help answer the question.

I printed some concentric circles on a piece of vinyl window material with my laser printer. Now by over-laying these circles on the chartplotter (and adjusting the charplotter scale for a suitable fit), I can clearly see that I am on the circle defined by these pieces of the arc.

Question answered. What a relief. Now to deal with the uncomfortably close boat- Maybe I can step over and bring him a cup of coffee while discussing a solution.

I should add that when I anchor, after putting out the proper 7:1 (or more) scope with my all chain rode, and letting the anchor "settle in", I back down hard to about 2000 rpm and hold it for 30 seconds while watching for relative motion between fixed range points to be sure I am set. That generally works well unless the bottom is weedy or otherwise not conducive for anchor resetting.

BTW, I made a few of these circle tools for my buddies. I have one extra if anyone would like it. First come, first served. Send me a PM.

 

[Stu Jackson]

Very clever, Rich, great idea.

 

[Head Sail]

Interesting plot but don't you want to know if your dragging anchor WHEN your dragging? I sleep much more relaxed with an anchor alarm set on my garmin 76c.

 

[Rich Stidger]

Interesting plot but don't you want to know if your dragging anchor WHEN your dragging? I sleep much more relaxed with an anchor alarm set on my garmin 76c.

That would be great, but in my area where boats anchor 150 feet from each other, an anchor alarm really doesn't cut it. By the time the alarm goes off, you are probably right on top of someone else or have missed them by sheer luck. Between the resolution of the anchor alarm and the need to set it to allow for swinging and flipping to the other side of the arc, those distances are greater than the distance between boats. Now if you tighten up on this setting you will be up all night with false alarms. I don't have a good solution for this.

 

[Head Sail]

Well knowing the next day if you dragged sure doesn't "cut it" either. Say you set your anchor alarm at 150 ft. , I think it would be better to know when you moved 151 ft than to keep on moving all night.

 

[Gunni]

Well knowing the next day if you dragged sure doesn't "cut it" either. Say you set your anchor alarm at 150 ft. , I think it would be better to know when you moved 151 ft than to keep on moving all night.

Swing alarm should be based on a circle. A 7:1 anchor scope in 10 feet of water would require over 100 feet of rode, and an alarm distance of more than 200 ft.
Somebody pulls in next to you and drops 75 feet of rope rode anchor at 5:1 on one of those boats that like to sail about on anchor and you got yourself a real demolition derby.

 

[Head Sail]

Somebody pulls in next to you and drops 75 feet of rope rode anchor at 5:1 on one of those boats that like to sail about on anchor and you got yourself a real demolition derby.

That would be a problem but the OP is about if YOU are dragging, not if someone violates your swing area.

 

[Rich Stidger]

I agree that I would like to know as soon as I drag. However unless you have a way to record the spot of your anchor set and then allow for the amount of rode, changes to the arc radius due to tide, and any additional distance of the GPS to the bow, I don't know of any way to set an accurate alarm. Then there is the matter of resolution for the alarm on the GPS. My GPS has steps of 0.01nm or 60 feet. So if you have 100 feet of rode out and your GPS is on the stern which is 40 feet from the bow, your circle radius is 140 feet. So that means that even if you can spot the anchor set location, your alarm can only be set for 120' or 180'. Neither distance works very well. Set for 120' and it will alarm all the time. Set for 180' and you are then accepting a 40' drag before notification.

The whole point of my circle tool was to confirm a drag problem at the earliest chance so that corrective action could be taken.

 

[Head Sail]

The whole point of my circle tool was to confirm a drag problem at the earliest chance so that corrective action could be taken.

While interesting, I don't see how your tool would confirm you had a drag problem at the earliest chance unless you were up all night watching it. 60ft is a small distance and hopefully ample time to discover you have dragged anchor while asleep. My little garmin hand held can be set in 1 ft. increments. Other boats anchor location is a problem solved by warning them they are in your arch. You want to know when you move outside your arch or drift into that pier 100 yard away.

 

[mz4wheeler]

Well, I always charge my phone/tablet at night... Just install "DragQueen" and let it run all night. No sense keeping a chart plotter on all night and draining your batteries.

 

[Rich Stidger]

Having a Garmin that can be set in 1 foot increments is the bomb! I have Drag Queen on my Android, but that still requires that you set the anchor drop point on your phone directly above the set. With my luck I would fumble my phone into the drink while I am trying to set the anchor!

 

[Alan Gomes]

Having a Garmin that can be set in 1 foot increments is the bomb! I have Drag Queen on my Android, but that still requires that you set the anchor drop point on your phone directly above the set. With my luck I would fumble my phone into the drink while I am trying to set the anchor!

I also use Drag Queen. What I do is when I bring the boat to a stop immediately before dropping the anchor, I hit the "mark" button on my Garmin to mark the position of the anchor (or pretty darn close to it, at least). Then I transfer that position to the Drag Queen app after I'm settled in. I find that it works pretty well.

 

[Rich Stidger]

I also use Drag Queen. What I do is when I bring the boat to a stop immediately before dropping the anchor, I hit the "mark" button on my Garmin to mark the position of the anchor (or pretty darn close to it, at least). Then I transfer that position to the Drag Queen app after I'm settled in. I find that it works pretty well.

Do you have a hand-held Garmin?

 

[Alan Gomes]

Do you have a hand-held Garmin?

No. It's a 546S.

 

[Rich Stidger]

No. It's a 546S.

How do you compensate for the position of the GPS antenna vs the bow anchor drop?

 

[Alan Gomes]

How do you compensate for the position of the GPS antenna vs the bow anchor drop?

I don't. It's only approximate but plenty close enough I think. My boat is 26 feet so the GPS is like 20 feet back from the bow. Plus, the GPS itself has a certain margin of error anyway.