Anchor Alarms?

[noelex 77]

Originally Posted by tedsherrin

I use my chart plotter anchor alarm. I've never had a problem with it, seems to be accurate. I turn it on after I set the anchor. As long as I put in enough radius, say .02 or .03 in heavier conditions it works exceptionally well.

It sounds like you are not setting a remote waypoint. Some chartplotters do not allow you to do this so you might not have an option.

The problem is that 0.02nm= 40 m (approx) and 0.03m =60 m. So the boat has to move more than 40-60m (or 120 to 180 feet) back before you get an alarm. In some cases with open anchorages this is fine. In other cases you will be on the rocks or colliding with other boats.

If you try to set a lower limit say 0.01nm you will get a lot of false alarms because as the boat swings from side to side the distance from the anchor alarm centre will exceeded this.

If you set a remote waypoint over your anchor as the centre of the alarm. With the distance = to the total of your rode length + distance from the bow to the GPS aerial then you only need to have a very small excess. The alarm will go off if you move only 5-10m further back. (5 is quite achievable with no false alarms, but you need to set things carefully)

You can fudge this with a chartplotter that does not allow a remote waypoint by setting the anchor alarm just before you drop the anchor (assuming you are moving backwards)

Setting the anchor alarm correctly is a bit more trouble but well worth it for the extra protection and lack of false alarms. (Apologies if I have misunderstood and you are already doing this)

The other consideration is that the chartplotter needs quite a bit of power (most vary between 1 and 3 amps even with the screen on full dim). If you use the anchor alarm all the time (and you should do) this is a lot of AHrs that need replacing.

[HappyMdRSailor]

Originally Posted by Wotname

Several threads recently have drifted into anchor alarms and rather than continue the drift, I thought to start a new more fixed focus discussion on anchor alarms - all poor puns intended

First a disclaimer, I'm not current with using anchor alarms, GPS, phone apps or whatever. In fact the last time I used an alarm was with a flashing rotary style depth sounder. Since then (decades back), I have just used shore transits, listening to the chain move over the bottom and so on. I do accept that time moves on and this thread should be about current and new technologies; so forgive me if what is now written is already old .

It seems to me that the best solution is to know if the anchor has moved , rather than the boat.

So do the GPS style alarms create a waypoint of the anchor position and then calculate if the anchor has moved? It seems to me in order to do that, you would need to enter in the scope and for the GPS to have a heading input. Do current alarms do that or do that just tell you if you have moved out of a circle whose diameter is entered by you?

Alternately, once the anchor is set, can you use the boats position and enter in the length of rode deployed along with the boats heading to establish the anchor position. From there, the alarm could monitor the boats changing heading and position and knowing the rode length, it could determine if the anchor has moved.

Comments???

I think you're dating all of us who comment on the rotary depth display... Hey... where is everybody???

And oh yea... That one thin band at 1/4 sounding must be a big bluefin parked under the boat...

Originally Posted by Palarran

I think your right that a lot of threads have touched on this but maybe none have solely focused on it. I use a Vesper Watchmate 850 AIS with anchor alarm. It uses almost no power when on. I then wired the dry alarm contacts to a Radio Shack security alarm in the boat (the watchmate is at the helm) and put a rheostat in series with it to adjust the loudness. It will for sure wake everyone up on the boat when it goes off.

We set it by dropping the anchor to the seabed. When it hits, the anchorman signals the helmsman to set the alarm and begin reversing. I have it set for meters and it's pretty accurate. We set out the scope we want based on chain markings then set the anchor. After setting and attaching the bridle we then back down for quite a while, like a minute, at 1000 to 1500 rpm and check to make sure the distance doesn't change. It will maybe vary by one meter back and forth during this process. We also record what the distance is away from the anchor for future reference. Then we set the alarm radius about 10 to 15 meters more than that distance and power down the diesels.

I'm sure someone will point out that if we swing 180 degrees the alarm will go off. It seldom does because the chain won't tension back up that much. If it does that's good so I can check out our new position.

I love this alarm - really it's way up there on my list of must haves.

Good illustration of what I prefer... Normal procedure for unknown anchorage or unfamiliar location=Setting the swing radius so that if I move more than 90 either way it goes off... If it's dead calm, radius is scope at the drop point...

[noelex 77]

This is how to look at the chartplotter trace and centre the anchor alarm radius at the correct spot. The chartplotter will display the track and it is usually obvious when the anchor was dropped. However this point needs to be displaced forward to allow for the displacement of the GPS antenna which is not normally at the bow.

[rwidman]

Originally Posted by Weyalan

Most boats these days have a GPS plotter and most GPS plotters have an anchor alarm. My experience of 3 or 4 different plotters is that they all work pretty much the same way - you input a distance slightly longer than your total length of rode and activate the alarm as the anchor hits the sea bed. It isn't fool-proof but it seems to work. I should say that the alarm volume on our plotter does seem a little less loud than desirable but fortunately I am a relatively light sleeper.

That works just fine and that's what I use. Most plotters have provisions for an external alarm and I have connected one to mine so I can hear it from the sleeping area.

If you didn't activate the alarm when you began to anchor you can just input double the length of rode to account for swings in a reversing tidal situation.

[noelex 77]

Originally Posted by rwidman

If you didn't activate the alarm when you began to anchor you can just input double the length of rode to account for swings in a reversing tidal situation.

You actually need 2x the length of the rode + 2x the distance from the GPS aerial to the bow + a margin for error.

In a typical anchorage for me with 40m of chain + 10m from the bow to the aerial +5m margin for error = 105m

This means in the original location, before the tide turns, the boat can drag over a 100m (330 feet) before any alarm occurs. Note that if your chartplotter does not allow a remote waypoint to serve as the centre of the anchor alarm and you forget to set the alarm when you drop there is no way around this (other than motoring back up to the anchor). If you try and set the alarm tighter than this you are guaranteed to get a false alarm.

There is a big difference between an anchor alarm that will trigger if you drag 5m, and one that will for 50% of the time need a shift of 105 m before it is triggered.

[zeehag]

set one and leave your boat..
let the others in the anchorage deal with the constant beeping when you are not there to correct it due to the normal wandering boats do when at anchor in windy and tidal areas....

[nigel1]

I also have the Vespermate 850.
For anchor watch, if the GPS antenna offsets have been correctly entered, and there is a heading input, then the unit plots the position of the bow when the anchor alarm is initiated.
Palarran mentioned fitting an external alarm. The inbuilt buzzer is not loud, but connecting an external buzzer is enough to wake the dead.
Lost count of the cups of coffee I have thrown over the deck when I forgot to disable the alarm leaving an anchorage.

[rwidman]

Originally Posted by noelex 77

You actually need 2x the length of the rode + 2x the distance from the GPS aerial to the bow + a margin for error..

If you want to get technical, you also have to remember that the rode is at an angle (the long side of a triangle) so the horizontal distance from the boat to the anchor is less than the length of the rode.

Me, I'm not that technical and my antenna is not that far from the bow so I just set the distance on the plotter to a little more than the length of the rode (and that's only marked every 30 feet anyway) and go to sleep. If the alarm wakes me I just go up and look outside or at the plotter screen to see if we are dragging. If not, I just add a few more feet to the circle and go back to bed.

Some folks like to do things the hard way. I'm not one of those folks.

[noelex 77]

Originally Posted by rwidman

If you want to get technical, you also have to remember that the rode is at an angle (the long side of a triangle) so the horizontal distance from the boat to the anchor is less than the length of the rode.

True, but it makes very little practical difference. For example with 40m of rode in 9m of water the difference is 1m. So the correct number is 39 rather than 40. For all practical purposes the trigonometry can be ignored at normal scopes.

[Paul L]

I'll third the Vesper WatchMate. I use its anchor alarm all the time. Supper low power, hooked to the boats main battery, attached to a loud external alarm. Just a simple, easy to use, reliable tool that doesn't consume much power.

[sy_gilana]

The best anchor alarm is a 100' long nylon cord with a diving weight on the end.
If you feel you need to set one, I feel that if I need to set an anchor alarm I have not anchored well enough, but hey sometimes circumstances demand you anchor in the less ideal spot.

I anchor as normal, then I dump the weight over next to my cabin hatch, pay out another 20' or so, and then drop the wooden X winder on the floor in my cabin. (Once I tied it around my toe) IF we drag or swing, the winder goes klunk-klunk on the sole, and I wake up. If we have just swung, I pull the weight under the boat again and go back to sleep.

No apps, no battery, no gps, no power drain its idiot proof.

[zeehag]

gilana--awesome!!!
i think the ones with LOUD external alarms need to sit their boat on anchor immediately next to someone with a briggs and stratton generator constantly running.
and, for that matter, please turn DOWN your cockpit vhf speakers.

[estarzinger]

I have anchor alarms in the plotter and in my vesper and my phone (4 different ones) and my ipad . . . . but I don't much use any of them as for me the best anchor alarm is me . . . . I pretty much instantly wake up if anything changes.

In any situation where I have any concern I do often leave either the plotter or vesper or ipad on with 1hz track points, so when I wake up I can just quickly glance at the screen and it will tell me what has happened/how the boat is now vs how it was.

[rwidman]

Originally Posted by sy_gilana

The best anchor alarm is a 100' long nylon cord with a diving weight on the end.
If you feel you need to set one, I feel that if I need to set an anchor alarm I have not anchored well enough, but hey sometimes circumstances demand you anchor in the less ideal spot.

I anchor as normal, then I dump the weight over next to my cabin hatch, pay out another 20' or so, and then drop the wooden X winder on the floor in my cabin. (Once I tied it around my toe) IF we drag or swing, the winder goes klunk-klunk on the sole, and I wake up. If we have just swung, I pull the weight under the boat again and go back to sleep.

No apps, no battery, no gps, no power drain its idiot proof.

I'm usually anchored in an area with reversing tidal current so I have to account for a 180 degree swing. That system wouldn't work well for me.

[Palarran]

I'm not sure I would be all that upset if I heard someone else's alarm going off. First, the alarms are usually inside and the boat is locked so the sound from 100' away isn't going to be that great. And it's better to be warned that something is amiss with your neighbor then find out when they bump into you. It gives you a chance to mossy over and check it out too. We are supposed to be friendly and helpful right.

We set ours every time we anchor, period. Even when we stern tie we set it. Why not?