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Old 10-07-2019, 04:22 PM   #1
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Positive Anchor Drag Detector System

I have designed a remote anchor drag detector that uses a sophisticated accelerometer to detect lateral anchor movements, a positive indicator of anchor slippage in real time, and transmits alarm information to a subscribers cell phone.

The advantages of this over GPS geofencing systems are apparent but include:
- detect movements of the anchor not the boat (don't wait until your boat is drifting to know your anchor is slipping)
- system is extremely accurate and eliminates inaccuracy and false alarms with GPS based systems
- gives positive indicator of initial anchor setting and any anchor slipping in real time (can be used to assist in anchor setting and retrieval)
- provides peace of mind allowing the boat owner to relax on the boat or onshore
- system utilizes a buoy to provide visual indication of anchor position to boat owner and other boaters

The system is simple and will be sold at a reasonable price point ($300-$500 depending on optional functionality such as designed for remote locations out of cell phone range).

Looking for feedback on the system and anyone interested in investing to develop the prototype and be part of the business development. I think marine insurance companies might also be interested in this additional safety device aboard their insured boats.
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Old 10-17-2019, 11:18 AM   #2
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Would appreciate any thought people have on this idea
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Old 10-17-2019, 11:36 AM   #3
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An adequate anchor and chain deployed with proper scope and set deeply should not drag.

I've been anchoring in the PNW for over 35 years and have not experienced a dragging anchor after it's set.

With careful anchorage selection and proper anchoring technique boaters should have peace of mind without resorting to anchor watch on plotters and other anchor antidragging alarms.
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Old 10-17-2019, 12:14 PM   #4
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Well, syjos' sentiments described above are admirable but not realistic. I think dragging at anchor is a bit like going aground. There are those who haven't yet but everyone eventually will if they boat enough.

I have found the gps based anchor alarms to be perfectly fine. If you have a smart phone or tablet they are part of many navigation apps as well as dedicated free anchor alarm apps.


I use mine by setting the anchor point where I end up after setting the anchor and just increase the alarm distance accordingly. But after a 180 degree wind shift it will often alarm. That isn't all bad because it wakes me up and lets me confirm that the anchor has set after the wind shift.

The better way is to set the anchor point where you drop your anchor.

So I don't need to spend another $300 on a new gadget.

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Old 10-17-2019, 12:38 PM   #5
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I set an anchor alarm and MOB over the anchor when deploying to monitor my position. Multiple chartplotters displaying my track also aid in monitoring the anchor hold.

I wouldn't bother to spend $100 to add to this level of protection, let alone $300-$500.
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Old 10-17-2019, 12:50 PM   #6
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An anchor "moving" and then re-setting after a current change is pretty common where we cruise. In 1 - 2 knot tidal areas with up to a 15 to 20 foot elevation change every 6 hours, anchor movement seems the norm. Like Flywright, our plotter and range markings seem to work fine.
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Old 10-17-2019, 12:54 PM   #7
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One cannot expect a GPS based system to work, unless rodes are quite short, using a BAhamian moor, or actually on a mooring ball. If you look at the anchored circle described by a fixed anchor and, let's say 100' of rode; that is a pretty large area. Also, you need some time to wake up, start engine(s), turn on CP, spotlights, etc.

The design challenge with an accelerometer based system is medium term drift. You need a double integration to get distance from accel. I would also think about using a heading sensor too, to establish a straight line drift.
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Old 10-17-2019, 12:55 PM   #8
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One cannot expect a GPS based system to work, unless rodes are quite short, using a BAhamian moor, or actually on a mooring ball.
I don't see why not. Ideally, you set the GPS point right over the anchor. And then size the warning circle based on how much rode you have out. If you haven't dragged, you can't move outside the circle. If you get outside the circle, you've dragged.
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Old 10-17-2019, 01:01 PM   #9
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I don't see why not. Ideally, you set the GPS point right over the anchor. And then size the warning circle based on how much rode you have out. If you haven't dragged, you can't move outside the circle. If you get outside the circle, you've dragged.
In addition, set the drag line function on so you can live monitor previous hour's activity. When I do this the minimal dragging and reset are immediately apparent. We do a manned anchor watch if in stronger winds or dodgy bottom.
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Old 10-17-2019, 01:04 PM   #10
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I don't see why not. Ideally, you set the GPS point right over the anchor. And then size the warning circle based on how much rode you have out. If you haven't dragged, you can't move outside the circle. If you get outside the circle, you've dragged.
Point well taken; I'm more thinking of when does a vessel actually hover right above a secured anchor? Answer: when they leave!
Also need to factor in GPS uncertainty; although I don't think that is a major issue, unless the fence is set too tight.
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Old 10-17-2019, 01:10 PM   #11
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Appreciate the responses. The system will also transmit to a cell phone so you can carry it onshore for peace of mind that your anchor is holding. Itís more than a gadget and the cost is just an estimate. I am going ahead with a prototype and hopefully users will see the advantage of a positive indication of anchor movement. A few hundred dollars is a small add to a very expensive vessel.
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Old 10-17-2019, 01:14 PM   #12
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Point well taken; I'm more thinking of when does a vessel actually hover right above a secured anchor? Answer: when they leave!
Also need to factor in GPS uncertainty; although I don't think that is a major issue, unless the fence is set too tight.
The boat won't be right above the anchor, but if I've got 200 feet of rode out, it'll definitely stay within 200 feet of it. If I swing around on a wind shift and it drags 3 feet and re-sets and I'm still within the circle, I'm not worried about that anyway. But if I've moved 20 feet, it'll break the fence and let me know there's a problem.
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Old 10-17-2019, 01:19 PM   #13
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Dave i think you understand what I’m getting at with the problems with a GPS based alarm. If I’m ashore it’s too late when my boat has drifted outside the geofence
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Old 10-17-2019, 01:37 PM   #14
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GPS advertised as 95% confidence in a 7 to 8 meter position. A lot of times, you will hit closer to 3 meters. So far so good. But.. what happens to the other 5%? Does your built in CP anchor alarm weed out that 5%? What exactly is the algorithm to prevent a single 15 meter fix from being used to false the alarm? I don't have all these answers, but these are the kinds of things to understand. And, what if I forget to set the alarm during the initial anchor drop? If I wait until the boat rides out on the hook, my center point of the fence is now 100' offset. And, who is going to drive up their boat to get a better fix above an already set anchor? no one. All part of the use case equation.
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Old 10-17-2019, 02:53 PM   #15
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Well, syjos' sentiments described above are admirable but not realistic. I think dragging at anchor is a bit like going aground. There are those who haven't yet but everyone eventually will if they boat enough.
I disagree that everyone will eventually go aground or drag anchor if boating long enough.. I've been boating since 1963 and big boat boating since 1985. We have never been aground, hit a rock or dragged anchor. Never been towed either.

Experience, knowledge, common sense and being careful and alert will keep a boater out of trouble no matter how long they boat. One should be less likely to go aground or drag, the longer one boats and becomes more experienced.

My wife and I have a rule that if one of us is uncomfortable with a situation whether navigating, anchoring or docking, we stop and asses the issue before proceeding.
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Old 10-17-2019, 02:56 PM   #16
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It's all about how conservative you are. Someone who only anchors in benign conditions with beefy gear is far less likely to drag than someone who plans to anchor anywhere and everywhere that might end up testing their limits more. Same with grounding. Someone who doesn't go into places that aren't at least a few feet above their draft and perfectly marked isn't at much risk. But someone who goes other places will eventually encounter a problem.
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Old 10-17-2019, 03:14 PM   #17
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It's all about how conservative you are. Someone who only anchors in benign conditions with beefy gear is far less likely to drag than someone who plans to anchor anywhere and everywhere that might end up testing their limits more. Same with grounding. Someone who doesn't go into places that aren't at least a few feet above their draft and perfectly marked isn't at much risk. But someone who goes other places will eventually encounter a problem.
We cruised the Broughtons, Queen Charlotte's and the inside passage for over 20 years. There are uncharted and unmarked rocks and shallows everywhere up there. Many of the anchorages get lumpy when the wind shifts direction or the anchorages become full of swells during extreme tide and current. Many anchorages require threading between rocks, trees and shallows entering via narrow entrances. Some require entrance at high tide only. Some narrow entrances required measuring depth with the tender before proceeding with the big boat. We also routinely raft a 40 foot and a 55 foot power boats alongside us on one 66 Bruce without dragging.

A careful knowledgeable boater should not experience any anchoring or grounding mishaps during their entire boating life. I know of at least 11 boaters who have boated longer than my wife and I with no mishaps.
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Old 10-17-2019, 03:27 PM   #18
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I appreciate all the useful discussion. I just donít see why folks wouldnít like a visual of an anchor on their device that shows that their anchor is set and staying set. I am a mechanical engineer and long time boater. I have teamed up with an electrical engineer to design the electronics. I have designed the deployment mechanism which is simple and foolproof. Within cell cover the system is simple and a bit more complicated for remote locations without cell cover. Is a couple hundred dollars for a reliable, positive indicator of anchor movement (distance and direction) really out of reach for most boaters? Certainly for new boaters without the years of experience some have this might be a useful add to their safety systems. The cost of a good meal in a nice restaurant for a boating family puts it into perspective.
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Old 10-17-2019, 03:52 PM   #19
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I also want to point out that this is not a device that floks with decades of experience in the PNW would want or need. However there are a considerable number of new and novice boaters that may not have the experience to give them the peace of mind to rely on a GSP system only, especially when on shore. There are also a lot of bareboat charter companies operating the the San Juan and Gulf Islands with people taking boats out that donít have much or any experience in the area.
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Old 10-17-2019, 04:04 PM   #20
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Well, syjos' sentiments described above are admirable but not realistic. I think dragging at anchor is a bit like going aground. There are those who haven't yet but everyone eventually will if they boat enough.

.
So the repeat offenders keep telling me.
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