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Old 02-23-2013, 02:54 PM   #61
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It was as my old time actual, and not hearsay, experience illustrates, successful to a degree. A boat clocking in a tidal current will usually trace and retrace a 180 degree arc, so little to no tangling involved. When wind shifts get crazy, combined with current shifts, and your track starts looking like a ball of twine after a cat got a hold of it... well then not so successful, just as Ron imagined. That's why people maintained an anchor watch in the form of a live person when things got complex.
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Old 02-23-2013, 03:04 PM   #62
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It was as my old time actual, and not hearsay, experience illustrates, successful to a degree. A boat clocking in a tidal current will usually trace and retrace a 180 degree arc, so little to no tangling involved. When wind shifts get crazy, combined with current shifts, and your track starts looking like a ball of twine after a cat got a hold of it... well then not so successful, just as Ron imagined. That's why people maintained an anchor watch in the form of a live person when things got complex.
That's why I added the caveat.....
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Old 02-27-2013, 11:24 AM   #63
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Some more!

Some additional Information from Active Captain

https://activecaptain.com/index.php :

More Anchoring Mathematics >>>

Wow, last week's item about anchor alarm math generated a lot of
comments, arguments, and ideas. It's amazing how anchoring brings this
out in people - and we didn't even say which type of anchor is the best!
Comments from multiple boaters pointed out that our anchor alarm distance
formula needed to take tide swing into consideration in order to add to
the accuracy. Perhaps it doesn't add much when you're in a 1 foot tidal
area but surely when the tide swing is something like 8 feet or more, it
really matters, right?

Well, actually, no. And after many nights at anchor in our home port
on the Penobscot Bay with 10-12 foot tides, trust me, it doesn't matter
at least as far as an anchor alarm goes. Good old Pythagoras and his
a^2 + b^2 = c^2 triangle theorem provides the proof.

Consider the triangle formed by your bow, anchor position, and the
location on the sea floor where your boat is located. That's a right
triangle which makes the math pretty easy. The hypotenuse (c) is the
anchor rode.

So let's go back to last week's example - a 42 foot sailboat with a bow
that's 5 feet off the water. We'll add that the anchor is set exactly at
high tide in 15 feet of water with a tide swing of 8 feet and a good
scope of 5:1 let out. This means 5 * (15 + 5) = 100 feet of rode is let
out. Using the Pythagorean theorem, the distance the boat is back along
the sea floor is: sqrt((100 * 100) - ((15 + 5) * (15 + 5))) = 97.98'
Fast forward to low tide and the distance the boat is actually pushed
back is now: sqrt((100 * 100) - ((7 + 5) * (7 + 5))) = 99.27'
Subtracting the two gives the amount the boat moved backwards because
of the tide swing: 99.27 - 97.98 = 1.29 feet or about 15.5 inches.
So that huge tide swing that took more than half the water away from
the anchorage will push the boat back by about a foot. That's something
that would be difficult to detect with today's technology.

Tide doesn't really matter for anchor alarms but tide swing has a huge
effect on scope. Now that's something to sit up and notice when you're
in an area with larger tides. Looking at this same example with our
sailboat anchoring at low tide this time, they'd drop their anchor in
7 feet of water and put out 5 * (7 + 5) = 60 feet of rode to get 5:1
scope. Now switch to high tide with 8 feet more water and their 60 feet
of rode is only giving 60 / (15 + 5) = 3:1 scope. Now that's dramatic
and might very well not be enough. We hear about boats dragging at high
tide in Maine all the time. This is why it happens.

We realize that the old salts among us know this well but recognize that
there are many skippers new to cruising who are part of our community.
It's a valuable lesson to remember to always put out scope for the
water depth at high tide. At anchor, we don't want either our anchor
alarm or yours going off!

One more thing.

Last week we mentioned that there wasn't a manufacturer who used heading
as an input into their anchor alarm along with the GPS location offset to
create a much more accurate anchor alarm. We were wrong. We were contacted
by Vesper who's AIS WatchMate 850 has a heading input capability and does
everything we've been wanting in an anchor alarm. It is an AIS transponder,
feeds back AIS info to other chartplotters or PC's, and has it's own low
power display for showing AIS or anchor alarm data.

Now we can be wrong about many things. But in this case, it is especially
embarrassing. You see, on January 25, 2012, the Vesper 850 was our Defender
1st product of the week. Honest - you can look it up in the newsletter
archive. For that week, the 850 was offered at about $900 which was an
unheard of price. As AIS has continued to get less expensive, prices have
dropped - the normal Defender price is $830 today and dropping it into your
shopping cart saves a few more dollars because of minimum advertised pricing
(just sayin').
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Old 02-28-2013, 10:33 AM   #64
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For those who are having trouble using the GPS anchor drag feature or feel that GPS is not accurate enough, here is a link to a device that's self contained and supposedly works better than the GPS anchor drag feature on a GPS:

Deep Blue Marine USA - Anchor Alert - Anchor alarm and monitoring system

Quote:
Deep Blue Anchor Alert is a revolutionary SONAR BASED electronic anchor alarm designed for any size power or sail boat. Anchor Alert monitors anchor movement and not boat movement so only if your anchor drags will it sound an alarm. This eliminates false alarms that are common to GPS anchor alarm systems. Additionally, this sonar based system will not fail due to interrupted satellite reception and can not be downgraded or turned off by third parties. GPS is great for navigation but don’t trust your boat or the safety of the people onboard to a 40 year old navigation technology.
No matter which way the winds blows or the current shifts your position the Deep Blue Anchor Alert knows exactly where your anchor is and if it is secure. Anchor Alert will keep track of anchor movement, accurate to less than a foot, and the alarm sounds only if your anchor moves beyond the limit you set.
The Anchor Alert’s computer processors will track all anchor movement and will know exactly where the anchor is at all times. This allows an anchor to swing 180 degrees in set and back again, all of which will be indicated, and only sound an alarm if the anchor moves beyond the allowable distance you set on the control panel.
No more sleepless nights worrying if your anchor is dragging or being jarred awake by false GPS anchor alarms. The Mobile Display works anywhere on your boat so, if it is one of those nights, take it to bed with you. If ever unsure of your anchor security a quick glance at the Mobile Display will let you know if you are dragging anchor or if you are secure. In the morning the Deep Blue Anchor Alert system will indicate any and all anchor movement that took place.
It is easy to install and Do-It-Yourself friendly with wireless technology. It can be permanently mounted with a thru hull fitting or simply lowered over the side
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Old 02-28-2013, 01:22 PM   #65
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Originally Posted by rwidman View Post
For those who are having trouble using the GPS anchor drag feature or feel that GPS is not accurate enough, here is a link to a device that's self contained and supposedly works better than the GPS anchor drag feature on a GPS:

Deep Blue Marine USA - Anchor Alert - Anchor alarm and monitoring system

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Very nice, but they sure want a lot of gold for this thing!
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Old 03-02-2013, 10:09 AM   #66
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Here's another approach to an anchor drag alarm: Anchor Alarm Project
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Old 03-02-2013, 12:26 PM   #67
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Here's another approach to an anchor drag alarm: Anchor Alarm Project
Very interesting...a slight improvement over the $3 string and weight trick but substantially less than the US Navy approved SONAR system priced at $3000 something!!!!!!
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Old 03-02-2013, 10:43 PM   #68
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Surely I can't be the only one on here who feels all the above is just too much kerfuffle..? Isn't it easier to just get a decent anchor, then check things if a wind or water movement change wakes you, as it always does. Another check when you go to the loo, as most of us do at our time of life, and all is well. Just ask yourselves, when was the last time you dragged....yeah...hardly ever, right..? And if you ever did, did it ever catch you unawares, or were you not already up, and checking anyway, because the weather change caught your attention already. Eggsactly.
I sometimes feel that posts like this make others who don't go to all this trouble fell they are somehow bad sailors. I feel with the gear we can get now, this sort of stuff is a bit passť. How many others out there don't go to all this extra trouble?
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Old 03-02-2013, 10:49 PM   #69
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Isn't it easier to just get a decent anchor, then check things if a wind or water movement change wakes you, as it always does.
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Old 03-03-2013, 03:06 AM   #70
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Surely I can't be the only one on here who feels all the above is just too much kerfuffle..? Isn't it easier to just get a decent anchor, then check things if a wind or water movement change wakes you, as it always does. Another check when you go to the loo, as most of us do at our time of life, and all is well. Just ask yourselves, when was the last time you dragged....yeah...hardly ever, right..? And if you ever did, did it ever catch you unawares, or were you not already up, and checking anyway, because the weather change caught your attention already. Eggsactly.
I sometimes feel that posts like this make others who don't go to all this trouble fell they are somehow bad sailors. I feel with the gear we can get now, this sort of stuff is a bit passť. How many others out there don't go to all this extra trouble?
Yeah I'm with you old mate! But perhaps "they" like it?! Gives them a sense of purpose?! Dunno .... Im not directly attacking anyone so keep to the sensitive members please ya knickers on, but me on the other hand, would rather direct my attention to more important things like what I am going to drink, where i am going to fish and dive and sleep peacefully knowing full well my SARCA's hold the floor like shit on a blanket.

On a side note tho, it is rather amusing watching it all tho lol
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Old 03-03-2013, 09:55 AM   #71
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Surely I can't be the only one on here who feels all the above is just too much kerfuffle..? Isn't it easier to just get a decent anchor, then check things if a wind or water movement change wakes you, as it always does. Another check when you go to the loo, as most of us do at our time of life, and all is well. Just ask yourselves, when was the last time you dragged....yeah...hardly ever, right..? And if you ever did, did it ever catch you unawares, or were you not already up, and checking anyway, because the weather change caught your attention already. Eggsactly.
I sometimes feel that posts like this make others who don't go to all this trouble fell they are somehow bad sailors. I feel with the gear we can get now, this sort of stuff is a bit passť. How many others out there don't go to all this extra trouble?
I don't think you read all the post, or possibly you read something into them that the poster didn't intend.

I have good ground tackle and know how to use it. I anchor, set the alarm on my chart plotter (why not, it's already there), and sleep soundly. I'm not looking for anything more, but some folks are, that's why I posted the link I posted.
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Old 03-03-2013, 10:09 AM   #72
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Quote:
Originally Posted by Peter B View Post
Surely I can't be the only one on here who feels all the above is just too much kerfuffle..? Isn't it easier to just get a decent anchor, then check things if a wind or water movement change wakes you, as it always does. Another check when you go to the loo, as most of us do at our time of life, and all is well. Just ask yourselves, when was the last time you dragged....yeah...hardly ever, right..? And if you ever did, did it ever catch you unawares, or were you not already up, and checking anyway, because the weather change caught your attention already. Eggsactly.
I sometimes feel that posts like this make others who don't go to all this trouble fell they are somehow bad sailors. I feel with the gear we can get now, this sort of stuff is a bit passť. How many others out there don't go to all this extra trouble?
If I let wind/wave ALWAYS wake me, as a liveaboard, I would never get any sleep. Plus sometime you have to anchor after an exhauting leg (for numerous possible reasons) and staying awake till the tide/wind changes isn't even in the cards.

As an assistance tower...dragging is far more common than you think.

If you anchor in some tight places...waiting for nature to wake you could mean you are already aground and in some places that could mean losing your boat.

So whether electronic or neanderthal, anchor alarms are a backup for the short handed or those few times that the unthinkable happens...kinda like why people have backups for everything else on a boat (or not )....either electronic or neanderthal...once familiar with whatever you choose only takes a few moments more to back up the great anchoring job/tackle we all are so proud of...
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Old 03-03-2013, 10:50 AM   #73
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The problem, Peter, is that we don't all KNOW that we have the correct ground tackle or have pushed it to the brink of failure. We sometimes can't do everything right and I sleep better knowing that IF the weather turn unexpectedly AND we may not have "the perfect anchor" that we can be awaken should we drag. Heck, there are countless anchor threads that say to me that there is no perfect anchor, nor, if we only have anchor x or anchor y on our boat but need anchor z (and we don't know it), again, I feel better with an ACCURATE alarm. That's all *I* am saying
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Old 03-03-2013, 11:03 AM   #74
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People, we're looking at this all wrong. We are trying to find a system to warn us if our anchor has moved on the sea floor but we are trying to do it by measuring the movement of the boat. At best, we can only set this up to warn us if the boat moves more than two times the length of the rode we have deployed.

The solution is simple - put a GPS on the anchor itself and have it warn us on the boat if the anchor has moved. Accuracy should be about ten feet.

All we have to do is find a way for the GPS to read the satelite signals underwater!
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Old 03-03-2013, 12:10 PM   #75
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People, we're looking at this all wrong. We are trying to find a system to warn us if our anchor has moved on the sea floor but we are trying to do it by measuring the movement of the boat. At best, we can only set this up to warn us if the boat moves more than two times the length of the rode we have deployed.

The solution is simple - put a GPS on the anchor itself and have it warn us on the boat if the anchor has moved. Accuracy should be about ten feet.

All we have to do is find a way for the GPS to read the satelite signals underwater!

LOL...Love it!
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Old 03-03-2013, 12:29 PM   #76
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This product takes into consideration that the skipper ALWAYS puts the anchor in the right place, lets out the correct amount of rode and knows without doubt every rock or shallow place in the anchorage.

WAY WAY too many assumptions. Contacting the bottom w/o dragging is easy to do. Of course I have experience.
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Old 06-06-2013, 09:58 AM   #77
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People, we're looking at this all wrong. We are trying to find a system to warn us if our anchor has moved on the sea floor but we are trying to do it by measuring the movement of the boat. At best, we can only set this up to warn us if the boat moves more than two times the length of the rode we have deployed.

The solution is simple - put a GPS on the anchor itself and have it warn us on the boat if the anchor has moved. Accuracy should be about ten feet.

All we have to do is find a way for the GPS to read the satelite signals underwater!
It would be great, but you don't need to be so precise.

You actually need to be informed when you are going out of a zone you have set as secure.

There are mobile apps that do that job pretty good. Some of them let you set a exclusion sector for you to be warned if the wind changes.

I have read comments about the problem of setting the right anchor position. This can be accomplished too in some mobile apps with a fine adjust after the anchor position has been set. You just need to input the actual bearing and the estimated distance to the anchor and the app changes the location of the anchor automaticaly.

And you don't need cell coverage, just GPS signal, to get it work.

Have a look to Sailsafe (for Android phones though):
https://play.google.com/store/apps/d...t.sailsafeFree

This app can be use even if you leave the boat. You can configure the app to call a second phone in case something happens. It even respons to sms commands with useful information like the current location of the boat, the bearing, a link to a google map with the position of the boat...

Hope this can help to those people that doesn't want (or can't) spend money in other specific on-board devices.
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Old 06-08-2013, 10:14 AM   #78
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Besides Drag Queen on my smart phone, I use "My Tracks" app on phone. it keeps detailed track info and is easier to tell what's going on.
Also use it whenever i'm underway.

i could use polar View on laptop, but it is getting a bit much.

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