Garmin Anchor Drag Alarm

[Spinner]

I use the WatchMate anchor watch function on my IPhone. It gets data via a Wi-Fi connection to the Vesper Marine AIS transponder. It’s pretty good, and doesn’t use up battery power. That AIS unit also can be hooked to its own audible alarm, but I didn’t do that because I get the same thing on my phone.

I also place a mark on the chartplotter where the anchor was dropped and a second mark where my boat ends up after setting the anchor. It’s not really necessary, but it is handy for watching the movement of the boat over the first 20 minutes or so.

I do take bearings on a few landmarks just for backup

 

[porman]

I was just playing with Anchor Pro on my I-phone and it seems that that GPS accuracy is stuck at 65 m . At that precision I'm "drifting" in and out of the allowed distance without moving.

What are other people who use Anchor Pro getting for GPS accuracy?

I just set it while sitting at home and the accuracy varies between 10.6 ft and 14.1 ft.

 

[Drake]

I’m a little paranoid about dragging anchor. In addition to buying a great anchor (has never drug once) I have used Anchor Watch for several years with good results. I also take several distance bearings with a golf laser range finder and monitor several times during the night. Makes me sleep better.

Paul

 

[JustBob]

I’m sorry but I haven’t been explaining this system very well. Hopefully this will clear up some of the confusion I created. My system doesn’t care where the boat is! A wind shift could move it 400’ or more and the alarm wouldn’t trigger if the anchor didn’t drag. Yet if the anchor only drags 5’-10’ the alarm would sound if you set it up to react quickly. So for those of you that anchor in fairly deep water this would be especially valuable.

I understand your design, but moving 5 to 10 feet isn't reasonable. Here in the PNW we have tidal swings greater than 10 feet. Your float's line can't be that tight. Also if your line is that tight and the anchor drags into deeper water your rig goes underwater.

Points for creativity though!

 

[Tin Man]

My experiences predate GPS... These anchor alarm uses and ideas sound splendid, but it sounds to me that all of you take extreme care and pride in making sure you don't drag to begin with - I certainly was very careful and watchful back in the day - but what do you do about the other guy? Laser tag them or such?

Once, a 3 boat raft nearly drag into me shortly after they dropped one hook - in spite of me blasting the horn to warn them off. Another time, a sailboat in the anchorage got stuck on the bottom at low tide and we swung into him... holding our boat off during a storm in the middle of the night was, uh, interesting.

 

[JustBob]

My experiences predate GPS... These anchor alarm uses and ideas sound splendid, but it sounds to me that all of you take extreme care and pride in making sure you don't drag to begin with - I certainly was very careful and watchful back in the day - but what do you do about the other guy? Laser tag them or such?

I don't disagree Tin Man. I have oversized anchor (176 lbs) and 1/2" chain. I set the hook with both engines.

But if I get the extra piece of mind with the working anchor alarm that's a bonus.

And yeah, what to do about the other guy? All we can do is watch out. I can run the low power digital radar along with a guard setting, but there are tenders, kayaks, etc. always going by, to that won't work.

 

[Tin Man]

I don't disagree Tin Man. I have oversized anchor (176 lbs) and 1/2" chain. I set the hook with both engines.

But if I get the extra piece of mind with the working anchor alarm that's a bonus.

And yeah, what to do about the other guy? All we can do is watch out. I can run the low power digital radar along with a guard setting, but there are tenders, kayaks, etc. always going by, to that won't work.

Oh. I didn't mean to imply that an anchor alarm was unnecessary. I would be all over that when/if I ever get my retirement vessel.

The radar guard setting sounds very interesting. Can either be set to warn on ex'es approaching?

 

[rbcooper]

Sahockey,

Ok everything you propose involves a bunch of predetermine exercises. You have to deploy your gps buoy right as you deploy the anchor. You're still subject to all of the "extra" error introduced by the need to deploy additional line to accomodate for tidal variations (or have some elaborate tensioning system). But the reality is that the boat itself will still swing in an expected arc based only on the amount of line deployed. You will NOT be alarmed any earlier than if the expected arc was properly specified. For example you set your anchor at xxx lat, yyy lon and deploy 100 feet of chain. The arc circumscribed by the 100 feet ( well it's not exactly that due to the vagaries of the depth but close enough ) will set the boundary of the alarm. Now during the night a heavy wind arises and pushes the boat in a direction that forces the boat to drag anchor. The boat won't drag anchor until the boat goes beyond the original circumscribed arc above. So your anchor drag warning is no better than the classic one. Assuming that the classic one is set at the point of when the anchor is set. That gets to my biggest complaint about most anchor alarms built into chart plotters and that is they require to set it while you're still trying to get the anchor set. So the smart phone apps that allow you to adjust the location for the anchor to a lat lon location are my go to ones. And how do you determine the exact location of the anchor set, after the fact? Well your chart plotter is your friend here. I have a bunch of experience on using the extremely over zoomed charts on my plotters. You can usually note exactly where you dropped your anchor and read the lat lon location from the display. Use this data in the smart phone apps and you can set your tolerance within 5 feet and be assured you will be notified if your anchor drags. Never had a false alarm. Well never dragged either to tell the truth.

RB Cooper

 

[sahockey]

RB Cooper

You are certainly correct that if you can accurately locate where the anchor is and how much rode is deployed that this would alarm as fast as my system. But that’s the rub. Accurately locating the anchor location! This is critical to all systems. You are apparently much more accurate than I’ll ever be to arrive at the exact spot (within 5’) using your chartplotter. If I and others could reliably do that then there would be no need to consider other anchoring alarm ideas. But in the places I’ve anchored I can state with certainty that I would never be able to get my anchoring location within even 50’ on any reliable basis. In fact I would not be comfortable saying that I could get it within 100’ very often. When you have a whole lot of water all around you with no land close it’s difficult to try and pin an area down to a small point irregardless of the detail your plotter shows. Of course one of the reasons being that anchors do not always set where dropped and depending on the bottom may require some distance before they set. The anchor studies I’ve read show that there are many variations to setting distance even with the same anchor type. Then of course the direction of that drag is another variable that is difficult for many of us to arrive at accurately what with currents, wind, and even how straight our boat does or doesn’t back.

You are right in saying that this method requires some type of tensioning system that may be complex in nature. But if you have a good tensioning system it’s an easy matter to attach a clip to your anchor and then throw the rope over with the attached gps, float, and tentioner combination before even lowering your anchor. That float would then end up above the location the anchor ends up setting at.

Although there is already a complex and accurate tensioner developed in Europe, which is quite expensive, I think a fairly simple shock cord sleeved around or next to a rope could work well if constructed of the right materials. It might be desirable to be able to make an adjustment for different depth ranges before deploying. Some common devices may be used to start to design a moderately simple tensioner could start as a tape measure, a fishing reel with drag setup, a battery drill with settings to keep it from over torquing screws, or even a dog leash that retracts.

If you can reliably know where your anchor ended up after setting and not just where you dropped it then any system you use will be pretty accurate since it’s fairly easy to arrive at your anchor rode length you let out. Of course that’s the critical variable to all anchor alarms, where is my anchor?

 

[sahockey]

I also wanted to add that I’ve never dragged.....yet. But I worry about it every time I anchor!
Stephen

 

[sahockey]

I understand your design, but moving 5 to 10 feet isn't reasonable. Here in the PNW we have tidal swings greater than 10 feet. Your float's line can't be that tight. Also if your line is that tight and the anchor drags into deeper water your rig goes underwater.

Points for creativity though!

JustBob

If your anchor drags into deeper water you would want to know so that you could increase your rode length to cover the increased scope. If your tensioner was properly designed then hopefully your float would still be above water over the float and your system would show where your anchor is after the anchor was reset. This would allow you to increase your anchor rode length to cover the increased depth. Furthermore after increasing your rode length, your alarm would still be set at this new anchor set position.

I agree that even with this system trying to narrow it down to only 5’ may be too close in many conditions. Yet one of the advantages of this system is that WHEN your anchor does drag and then you get it dug in again you can reset your warning device with the push of a button so that you don’t have to stand guard the rest of the night.

Stephen