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Old 28-02-2010, 22:09   #31
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How about this? (It's a bit like "a train leaves Chicago going 80MPH ..) Come to think of it, 306 feet is a long drag, so it would be better to calculate the point directly above the anchor and allow 153 feet of drag from that point.
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Old 28-02-2010, 22:26   #32
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I would like an anchor alarm that would send a message on my cell phone when I am ashore.
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Old 28-02-2010, 22:32   #33
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I want my anchor alarm cell phone to call the boat that I am dragging down on.

Then I could a peacefull nights sleep not having to worry about the batteries running down as I would not need an anchor light.
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Old 28-02-2010, 22:34   #34
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Going ashore

I'm trying to train my dog so that when I'm ashore he reads the chartplotter and barks out a warning if the anchor starts to drag...he's doing good but he's kind of a slow learner...so far he's just up to crapping in the cockpit.
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Old 01-03-2010, 07:19   #35
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How about this?
There's one complication that you're not considering. When you drop your anchor and press the "set anchor alarm" button or obtain a waypoint, you're getting the position where the GPS is located and not the anchor/bow position. This adds 2G to the error when you swing around assuming the GPS stays in the same position on the boat.
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Old 01-03-2010, 07:47   #36
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The attached .doc file contains an explanation of the issues surrounding the anchor alarms that are implemented today on almost all devices. It shows measurements on "graph paper" to show what happens. After you look at it, I think you'll begin to appreciate how bad almost all anchor alarms are.

It's true that if you can take the GPS to the bow when you drop the anchor, a lot of the error can be removed. But that's a pretty rare type of alarm. It's one of the advantages of R_C's portable anchor alarm. Dropping his portable device overboard while letting out rode would be a disadvantage. Adding a heading sensor would allow all of the error to be removed and the box could be placed anywhere.

Another thing I'd like in an anchor alarm is an angular warning. In other words, there are times when it would be nice to have an alarm when you swing into an area that you don't want to be in. It kind of needs to be a "bundt-cake" alarm area because if the winds die, I'm OK with turning around close to the anchor position. Slide a little further out and I'd like to know.

The other thing that I'd like in an alarm is the ability to show a track of where you've been graphically - displaying a ring after a day or so. That would give you an idea about where you've been and how far you've been pushed back there before at each angle. It would also give you an idea about anchor reset as it flips. Finally, I'd like the option of displaying the whole thing on a nautical chart because if I get woken up, I want immediate info about where I am and what I need to do.

Anchor alarms are much more complicated than the simple implementations provided by all manufacturers today.
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Old 01-03-2010, 07:49   #37
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i like the anchor alarm .. very creative. i have been looking for a simple low priced handheld gps that gives an LCD readout of the lat/lon (no maps or waypoints or anything). i know they should be cheap cause i bought a usb gps device for 20 bucks.
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Old 01-03-2010, 07:53   #38
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There's one complication that you're not considering. When you drop your anchor and press the "set anchor alarm" button or obtain a waypoint, you're getting the position where the GPS is located and not the anchor/bow position. This adds 2G to the error when you swing around assuming the GPS stays in the same position on the boat.
I agree. The best anchor alarm geometry begins with a good approximation of the location of the anchor. Once you know the center of the circle, you just calculate an appropriate radius.

With my anchor alarm, our anchor mark position is usually within 20 feet of where the anchor sets. If I wanted better accuracy, I could always add a trip line and float to the anchor then dinghy out with the anchor alarm, pull the trip line taught and mark the position. I don't use a trip line because I'm not too concerned with the 20 foot error. It does mean when I swing around 180 degrees I'd need to drag 40 feet before the alarm would sound. But I always pad the radius to accommodate GPS error anyway.

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Old 01-03-2010, 08:12   #39
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Your alarm is beautiful.

But I think a word or two needs to be said in the defense of conventional implementations. Don't forget we've got a certain amount of position error. This by itself makes it futile to try to precise the position of the anchor beyond a certain point. A conventional anchor alarm does NOT, as a poster above explained, distinguish between swinging/no drag, and dragging off in the same direction you set the anchor. This is not a big deal if you set the alarm radius right. I don't mind being woken up for a swing -- obviously that is not the immediate crisis that a drag is, but you need to know whether you're swinging into other boats, which you may well do if people around you are anchored with different scope.

But what is really missing from your otherwise lovely device is a picture of WHERE you are. In my opinion, the best possible anchor alarm system is a chartplotter in the master cabin, if you have a multistation electronics system. You can not only set and monitor your anchor alarm from there, you can see at a glance, without getting out of your bunk, what's going on, where you are pointed, whether you are swinging or dragging, etc., giving you complete spatial orientation. A swing shows up as a heavy arch on the plotter. A deviation from the normal swing radius is immediately visible. How many skippers, like me, lose sleep because you feel compelled to get up every hour or two, poke your head out of a hatch, and check your landmarks to get oriented? A chart plotter in the master cabin would be so much better.

You can also set a depth alarm as a second warning.

On top of that, you can use it on passage when you're off watch, to see speed, progress, direction, even depth and wind information.

I think it's an overall better solution, not requiring new product development to boot. But I do say that for the narrow purpose of a very precise measurement of where you are in relation to your anchor, your widget looks fantastic.
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Old 01-03-2010, 08:23   #40
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The other thing that I'd like in an alarm is the ability to show a track of where you've been graphically - displaying a ring after a day or so. That would give you an idea about where you've been and how far you've been pushed back there before at each angle. It would also give you an idea about anchor reset as it flips. Finally, I'd like the option of displaying the whole thing on a nautical chart because if I get woken up, I want immediate info about where I am and what I need to do.
But why add these features to an anchor alarm when they already exist in your chartplotter? I firmly believe in keeping things simple especially where software and electronics are concerned. I only want my anchor alarm to alert me when my anchor has dragged. That's its primary purpose and the more advanced features you describe can probably be accomplished with other tools.

- Rick
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Old 01-03-2010, 08:34   #41
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But why add these features to an anchor alarm when they already exist in your chartplotter?
Because the chartplotter isn't laying there next to me in the bunk. And just like the previous poster remarked, there's a nice advantage of being able to see the status at night.

Maybe I'm alone in thinking it's important. All I know is that it's what I've been doing for the past 3 years and I couldn't imagine going back to a numeric display.

Here's another twist for your product. In addition to the LCD display (or even replacing it...) put in a simple WiFi radio. Now you can keep the anchor alarm in a nice, safe place, and allow me to use my phone for the output, alarming, etc. All phones today have incredible graphics ability. And a picture is worth how many words?
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Old 01-03-2010, 09:14   #42
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I like the idea of the second anchor and bucket idea.... I have in the past, anchored where to bottom was muddyand hooked up a simple alarm of a second anchor and pan and a fender tyed to it.. run the line fron the front to the back of the boat.. if the anchor drags, the pan and fender bounce down the side of the boat.. The reason for the fender.. I lost the first pan and an anchor the first time it draged...
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Old 01-03-2010, 09:23   #43
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Jeffrey,

In my NavMonPc (I know, Windows PC app, power drain, etc.), you are able to display the 24-hour track of your boat (its GPS position), and you can set/reset the center of the anchor watch circle. This lets you swing on your anchor for a while and you can then set the watch-circle center and radius to best fit the situation.

If the alarm sounds you can look at your position track and determine if you are dragging or if you just need to modify the watch-circle. I've had good reports about the usability of this design. It lets you manually eliminate the built-in watch-circle centerpoint error caused by the typical anchor@bow, GPS@stern situation.
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Old 01-03-2010, 09:51   #44
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RC,
Since you asked what others are using...
I use a Garmin 76CSx handheld plugged into a 12V outlet in the forward cabin where we sleep. It draws less power all night than the two reading lights we use for an hour before bed. It draws a track of where we have been so if the alarm does go off I can see clearly where we are compared with where we have been. Keeping it in the forward cabin right next to my head it is <10' from the bow so no worries about the swing arc of the stern vs the bow. Best of all, the alarm goes off when we pull anchor if I have forgotten to turn it off and unplug it keeping our backup GPS physically isolated from the electrical system on the boat.
Hope that helps.
--Eric
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Old 01-03-2010, 10:18   #45
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There's one complication that you're not considering. When you drop your anchor and press the "set anchor alarm" button or obtain a waypoint, you're getting the position where the GPS is located and not the anchor/bow position. This adds 2G to the error when you swing around assuming the GPS stays in the same position on the boat.
I've allowed for the 2G, it's in the equation where the circumference of the swing circle = 2(Y+G).

Also, you do not log the anchor set point until you are dug in, at scope, and reversing at half revs stretching the rode out straight. The issue is that even at a moderate 5:1 scope in 15 to 20 feet of water, this results in a very large allowance that must be made. Better to figure out where the anchor is and allow the radius of the circle plus a margin.

It's "just" mathematics, but what is needed is something to offset the GPS position with the calculated Y+G to get the actual placement of the anchor.

Cheers
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