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Old 03-26-2019, 01:56 PM   #1
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An Anchor alarm that detects drag in 10’

Hi forum,

I responded to a thread about a Garmin anchor alarm asking opinions on this idea. In hindsite it is probably more appropriate to start my own thread. Please read this and comment on any shortcomings to this concept. I’ve enjoyed the reasoned and knowledgeable responses from members of this group and look forward you critiques.

Most anchor alarms depend on a large circle with the radius being the length of your anchor chain deployed. This is necessary because of swinging at anchor which could even involve up to a 180 degree wind or current shift. Of course the problem with this is two fold. 1. The center of the circle is difficult to mark while anchoring. 2. The length of rode let out is affected by how tight it is to the anchor. If either of these aren’t accurately marked there will potentially be a large error possibility causing false alarms or even worse no alarm in time. In today’s crowded anchorages this is a serious shortcoming.

The concept I’m advocating does not track the boat through its swings. It only tracks the anchor. Thus the boat could move 400’ (with a scope of 200’ out) and the alarm would not sound unless the anchor moved 5’ to 10’ or any longer amount you decided was safe.

Get a gps locator that is powered by a battery in a waterproof design. There are many small variations of this used for tracking wayward dogs. You would want to get one that does not require a monthly fee. They come with software that allows you to set it up most anyway you desire. Attach this locator to a float that would keep it above the water. Tie that float with a rope to the trip location on your anchor with a device in between which keeps the float directly or almost directly over your anchor. This device could be an adjustable shock cord or even a more complicated device that maintains tension on the attachment rope to adjust for tides and currents to keep the float above your anchor. Thus the center of your circle is marked and the alarm is independent of the amount of rode you have out. An additional benefit of this method is if your anchor gets snagged you have a trip rope you can use to get it free. What do you think?
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Old 03-26-2019, 02:19 PM   #2
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While I like the idea, I think the practicality of it will be challenging.

I foresee an expensive water logged device, or worse yet one gone missing.

Coupled with having to retrieve the device to charge it if at an anchorage for multiple days might be more problematic.

I have had excellent results with Anchor Pro. Anchor has never dragged, but we have simulated a dragging and the alarm is very accurate and would wake up the dead.
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Old 03-26-2019, 03:21 PM   #3
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Hi forum,

I responded to a thread about a Garmin anchor alarm asking opinions on this idea. In hindsite it is probably more appropriate to start my own thread. Please read this and comment on any shortcomings to this concept. I’ve enjoyed the reasoned and knowledgeable responses from members of this group and look forward you critiques.

Most anchor alarms depend on a large circle with the radius being the length of your anchor chain deployed. This is necessary because of swinging at anchor which could even involve up to a 180 degree wind or current shift. Of course the problem with this is two fold. 1. The center of the circle is difficult to mark while anchoring. 2. The length of rode let out is affected by how tight it is to the anchor. If either of these aren’t accurately marked there will potentially be a large error possibility causing false alarms or even worse no alarm in time. In today’s crowded anchorages this is a serious shortcoming.

The concept I’m advocating does not track the boat through its swings. It only tracks the anchor. Thus the boat could move 400’ (with a scope of 200’ out) and the alarm would not sound unless the anchor moved 5’ to 10’ or any longer amount you decided was safe.

Get a gps locator that is powered by a battery in a waterproof design. There are many small variations of this used for tracking wayward dogs. You would want to get one that does not require a monthly fee. They come with software that allows you to set it up most anyway you desire. Attach this locator to a float that would keep it above the water. Tie that float with a rope to the trip location on your anchor with a device in between which keeps the float directly or almost directly over your anchor. This device could be an adjustable shock cord or even a more complicated device that maintains tension on the attachment rope to adjust for tides and currents to keep the float above your anchor. Thus the center of your circle is marked and the alarm is independent of the amount of rode you have out. An additional benefit of this method is if your anchor gets snagged you have a trip rope you can use to get it free. What do you think?
Sounds like a great idea and the issues are likely surmountable with current technology. Hope you work on it. I'll buy the first one
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Old 04-03-2019, 05:18 AM   #4
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“It was a dark and stormy night” at least this is what Snoopy’s weather forecast called for. With winds forecast out of the west Snoopy found an island on his chart that showed good holding ground on the eastern side.

Of course the best laid plans of men and dogs may soon need to be changed. So at 2am when the wind shifted 90 to 180 degrees blowing his boat towards the island and pulled his anchor free, Snoppy’s anchor alarm sounded. Snoopy reset his anchor and then with the push of a button rebooted his alarm. Back to dreams of the Red Barron.

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Old 04-03-2019, 07:00 AM   #5
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Most anchor alarms depend on a large circle with the radius being the length of your anchor chain deployed. This is necessary because of swinging at anchor which could even involve up to a 180 degree wind or current shift. Of course the problem with this is two fold. 1. The center of the circle is difficult to mark while anchoring. 2. The length of rode let out is affected by how tight it is to the anchor. If either of these aren’t accurately marked there will potentially be a large error possibility causing false alarms or even worse no alarm in time. In today’s crowded anchorages this is a serious shortcoming.

The concept I’m advocating does not track the boat through its swings. It only tracks the anchor. Thus the boat could move 400’ (with a scope of 200’ out) and the alarm would not sound unless the anchor moved 5’ to 10’ or any longer amount you decided was safe.

Get a gps locator that is powered by a battery in a waterproof design.... Thus the center of your circle is marked and the alarm is independent of the amount of rode you have out. ...What do you think?

Good to go full into problem-solving mode, might work, hard to say whether it might be commercially successful...

Maybe before you set out down that path, try this:
- anchor (confirm well set)
- drive back up to the anchor, so you're directly over where it's set, but without pulling upward on the shank.
- stand on the bow or pulpit directly above the anchor and record position*
- back off and payout a specific -- known -- amount of rode appropriate to your depth and conditions
- use known anchor position and known rode length to start your favorite anchor watch app, set your GPS accuracy alarm and you alarm radius accordingly, etc.

*Drag Queen on a cell phone works well enough for that. Or whatever apps you like.

-Chris
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Old 04-03-2019, 08:29 AM   #6
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Old 04-03-2019, 08:30 AM   #7
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Hope it works out.

For many of us, the right (constantly debated) over sized anchor with the correct rode shouldn't drag. If it does, you've got the wrong setup and equipment - or chose a bad bottom.

The question of course, as you are chasing, is detecting drag. We do it with the plotter track function turned on. Perfect, probably not. When anchored in strong winds, for us +25 knots, the crew goes to anchor watch mode watching the track, nearby boats that could be dragging and for low tide impediments.
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Old 04-03-2019, 09:40 AM   #8
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Chris and Sunchaser, thanks for your well thought out reply’s and suggestions. An additional problem I and some other boaters are faced with is that we are often Short Handed (this is the name of my 30’ Sundowner tug/trawler) being the only person on board. This makes some tasks more of a challenge especially when anchoring. So I try to use any advantage available to achieve the different tasks one must complete to have a safe, easy, successful, and thus fun time.

I must admit that I do also enjoy trying to find solutions to problems I run into. I lose a lot of sleep thinking of different ways to achieve my results but if I can come up with a better solution to a problem than I currently use it’s rewarding for me. Also I’ve always felt some of my best ideas �� were developed from other people’s ideas. So I don’t need ownership of ideas to feel that sense of reward. I don’t have the desire to go commercial with anything but will leave that to those with the drive and entrepreneurial spirit.
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Old 04-03-2019, 09:46 AM   #9
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The only two problems I see are:

1) Float on the anchor. there is a chance that boat passing through the already tight anchorage fouls on your float line and now you're both drifting.

2) wind shift, you drift across your own float and foul your running gear in your float. (I' have seen this happen more than once). Now your anchor and boat are dragging together and the distance never exceeds the alarm threshold.
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Old 04-03-2019, 09:58 AM   #10
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Does anyone know how far GPS signals can go through water?
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Old 04-03-2019, 10:25 AM   #11
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Does anyone know how far GPS signals can go through water?
RF signals can’t propagate well under saltwater.
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Old 04-03-2019, 11:14 AM   #12
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Shrew, I agree this is a potential problem. But since the rope holding the float is tight to the anchor it shouldn’t be any worse than being in a mooring field with all those floats surrounding you. The floats that are tight to the line going down tend to keep the float on the surface next to but not under your boat. It would be worse if the float was not held down tight to the anchor (of course it is still above water) as is the case with some of the lobster traps I’ve had to avoid when boating in Maine. Those traps had two floats tied to each other with one of them tied to the traps below. I regarded these as boat traps since you always tried to avoid going in between the two traps tied together. I noticed some of the ropes tying the floats together were tied with floating line. Hopefully this is illegal. Thanks
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Old 04-03-2019, 11:14 AM   #13
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Sometimes a radius is fine. But more often, when I really need an alarm, it's because I'm anchored close to some hazard, like rocks. Rather than distance from the anchor, it's distance from the rocks, especially if it starts decreasing, that I really care about.

There are anchor alarms which let you set guard zones, but that takes some effort. Usually more than I'm willing to invest. I probably should practice more and get good at it though.

Maybe the solution is a combination of GPS, electronic charts and AI. The AI would replace me getting up every so often to analyze the pattern my track left on the chartplotter. A nice arc means I can go back to sleep. Multiple arcs mean it's either dragging and catching, or the wind kicked up and straightened out the rode, and I can't go back to sleep yet. A straight line means fire up the engine and wake up the crew.
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Old 04-03-2019, 12:56 PM   #14
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"Thus the boat could move 400’ (with a scope of 200’ out) and the alarm would not sound".

Why would you want the alarm to sound within that 400 foot diameter of your anchoring area?

The only time it may be be an advantage, would be in crowded anchorages where another boat is dragging your anchor, and they are pulling your boat against the wind/current towards the original anchor position.

Under any other case you will be outside that 400 foot circle if your anchor drags.
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Old 04-03-2019, 02:03 PM   #15
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AusCan, as you pointed out you wouldn’t want your anchor alarm to sound unless you were outside the 400’ diameter. And in this system and most others it wouldn’t. A 10’ anchor drag equals a breach of the 400’ diameter zone by 10’ on one side. I’m sorry if I muddied the waters by adding that sentence.
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Old 04-03-2019, 02:26 PM   #16
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Someone made a stand-alone anchor alarm that does this: Boathooked.com: Anchor Alarm

I have one, but have never really put it to the test. First is that we don't anchor out much. Second is that the Neuse is pretty calm and we just don't go out if it looks like foul weather... you know, weekenders and all. :-)

I was going to dust it off this year and see if it still is up to the task. I mean, it was built before GPS and cell phones took over (2008). Still, I love the idea. It just needs to be modernized. I may drop a line to Rick and see if he has done anything new, with it.
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Old 04-03-2019, 09:10 PM   #17
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Thanks for the information. I think this is a fairly good system that has the main shortcomings most systems have. 1. Where did my anchor end up after setting? 2. If your anchor does drag at night in high winds or current how do you locate the new location for your anchor after resetting it? Go out in your dinghy and try to pull up the rode until you reach the anchor at the same time your boat is being held in place with this anchor and rode? Good luck with that!
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Old 04-04-2019, 12:23 PM   #18
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Another advantage of this system is it doesn’t matter how much rode you have out. So if your anchorage is getting crowded with a bunch of boats using short rodes you can shorten yours as much as you are comfortable with. You don’t have to change your alarm setting. Then on the other hand if you wake up in the middle of the night and the winds are starting to pickup you can lengthen your rode even though your distance markers are missing because you don’t have to change your alarm settings. And we all hopes this never happens but if the anchor alarm goes off in the middle of the night reset your anchor and then just reboot your alarm and you are ready to go back to your bunk.
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Old 04-13-2019, 09:56 AM   #19
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Completely agree radius isn’t great, however when added with radar overlay and proximity alarm it’s perfect. If you leave the “show my track” on it’s pretty easy to see if you are moving beyond your natural depth/scope radius of swing. The radar helps with other boats, especially those with a different swing pattern.
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