Anchor watch - electronic or sit on deck?

[noelex]

So bearing in mind your 55kg Rocna and obvious ability to properly set your gear, how many times have you actually dragged when an anchor alarm would have been of help? Genuine question, not just being argumentative.

The point I was making in an earlier reply (actually to someone else) was that in settled weather in the Solent he had been woken by a false alarm or maybe more than one, in conditions when a genuine problem would be most unlikely.

The Rocna has not dragged. The anchor alarm has woken me on 2 occasions, with other anchors, when I would not have realized I was dragging without it. The other times I have dragged the GPS alarm confirmed what was already knew (or were before GPS was fitted)
Saving the boat from damage twice in the last 20 years not much, but enough to earn its keep. Certainly more use than the life rafts and EPIRBS which have never been used, but I wouldn’t be without.

 

[Cruiser2B]

Oh no you haven't

I've been Lakesailored!

bbq's post was before yours. My advice was additional to both bbq's and your recommendations. When you plan for a safe swinging circle you calculate max scope, length of boat and a safety margin that will keep you from swinging onto the rocks; when you set your guard range, it should only be length of scope out and distance from bow to GPS antenna - and it should be centred on the actual position of the anchor.

 

[supra30]

The point I was making in an earlier reply (actually to someone else) was that in settled weather in the Solent he had been woken by a false alarm or maybe more than one, in conditions when a genuine problem would be most unlikely.

Ah... I think you've failed to grasp what I was trying to do with the alarm setup.

I wanted to be woken when the boat swung significantly, so I could eyeball proximity of other vessels.

Once I had seen several swing events, I was happy and slept the remainder of the night.

If I'd been in an anchorage with less nearby vessels but more worry about dragging, then I'd have set the alarm very differently, and probably not been woken at all.

Regards,

Mike

 

[noelex]

There is also the question of power used, even though we were not short of capacity or ability to charge at anchor (big solar panels and wind genny), because even a small GPS/Plotter will use about 0.5A. That may be relatively small but is still 12Ah per day and we often anchor for long periods.
.

A b/w GPS with a plotting function such as the Furuno GP-32 will consume less than half of this (under 0.2A). A handheld GPS will consume will use less again about 1/4 of the Furuno. Mount one of these near your bed. If you anchor often it will be cheap insurance and it will give you a backup GPS if your primary unit fails.
A couple of AHrs is not much to "spend" on a crewmember that keeps a constant watch on your position and will wake you up if there is a problem.

 

[Robin]

A b/w GPS with a plotting function such as the Furuno GP-32 will consume less than half of this (under 0.2A). A handheld GPS will consume will use less again about 1/4 of the Furuno. Mount one of these near your bed. If you anchor often it will be cheap insurance and it will give you a backup GPS if your primary unit fails.
A couple of AHrs is not much to "spend" on a crewmember that keeps a constant watch on your position and will wake you up if there is a problem.

Never felt a need for a handheld GPS as we had backup main units. On our last boat we had fixed 3 plotters, one with built in GPS and two with separate GPS. We had three entirely separate battery banks, 2 services and one engine & windlass so were well covered with backup GPS. The Yeoman was additional paper plotter but did run from any one two of the main GPS senders. A handheld would have seemed a bit OTT.

An alarm would only wake me if the boat, or at least the electronic doppleganger of it, had strayed beyond a certain amount. It would not tell me if another boat was about to swing into or drag down on us, it isn't that intelligent and it only yells out loud after the event not before! A radar guard alarm might warn of an approaching bumper beforehand but at a very high cost in amps indeed.

Anyway power usage is a side effect only not my main reason for not employing a bunch of alarms. If we had a history of dragging anchor or maybe just felt too insecure as I know some people do, it might be different, but we have years of confidence in doing things as we do and see no need.

From Supra30

Ah... I think you've failed to grasp what I was trying to do with the alarm setup.

I wanted to be woken when the boat swung significantly, so I could eyeball proximity of other vessels.

Once I had seen several swing events, I was happy and slept the remainder of the night.

If I'd been in an anchorage with less nearby vessels but more worry about dragging, then I'd have set the alarm very differently, and probably not been woken at all.

Regards,

Mike

That makes more sense to my original interpretation, although other than in wind over tide situations which I try hard to avoid, usually most boats swing more or less in unison.

I still say if I was concerned about dragging enough where we were anchored to want to set an alarm, that I would prefer the other (better IMO) option of re-anchoring where I was more confident of staying put. The problem to be solved surely is not to know when a feared drag starts but to ensure that it does not happen in the first place!

I probably come from a different era. Marinas were very rare beasts back when I started even on the South Coast UK and anchoring was therefore second nature. By the same token there were no electronic aids much other than the original Seafarer echosounder. I can understand it must seem very different now to people taking up cruising when most boats are marina parked and a night on a visitor buoy is almost an adventure.

Anyway safe sailing and anchoring to all.

 

[noelex]

An alarm would only wake me if the boat, or at least the electronic doppleganger of it, had strayed beyond a certain amount. It would not tell me if another boat was about to swing into or drag down on us, it isn't that intelligent and it only yells out loud after the event not before! A radar guard alarm might warn of an approaching bumper beforehand but at a very high cost in amps indeed.

The main use of an anchor alarm is to warn when your boat is dragging. If, however, you have a unit with an offset anchor alarm (where you can choose any position and the GPS will alarm if you move your chosen distance from that position) The GPS can be set to raise an alarm when the your boat swings in a certain direction. I have used this on many occasions and it is reliable.
The GPS will then wake you when a suspect boat is front of you (if concerned about the other boat dragging). Or when a suspect boat would be likely to swing into you (because it anchored to close). It doesn’t tell you when another boat is going to hit you, but it does at least warn you when you need to worry and allows for sleep the rest of the time.
Usually in these situations it is better to move but an offset anchor alarm especially if combined with a wind speed alarm is a useful alternative to moving, or staying up all night.

I have only used a radar alarm on 2 occasions as usually the GPS and or wind alarm are enough warning. As you mention the energy cost is high, but no more than a fridge, and it can be reduced with timed transmissions.

I think we will probably have to agree to disagree on the usefulness of alarms, but I started sailing before GPS was available and learnt when you lie at anchor almost everyday these electronic toys do make life easier and more secure. Think of them as an extra inexperienced crew member that can be told to wake the skipper if the boat drags, swings a certain way, or the wind picks up.

 

[DaveS]

I haven't been Lakesailored!

Apologies! bbq's post and mine were 5 minutes apart, so effectively contributed in parallel. Because I read the thread "threaded" rather than "flat" I didn't spot this, but I should of course have checked properly. Mea culpa.

Your point re. setting the guard radius is fair: my GPS aerial is mounted about 0.5m from my stern so I simply add scope to boat length, but with other installations the difference could be more significant. For ultimate accuracy, presumably (unless you've got the offset facility others mention) the "mark" button should be pressed when the plotter's aerial rather than the bows is directly over the anchor? I can see practical difficulties in knowing exactly where that is unless you use an anchor buoy and motor up to it once the anchor is set. (Hopefully the chain won't snag on anything too important as it's dragged under the boat... ) A less accurate but more practical option would be to position the boat head to wind a few metres ahead of where you want to lay the anchor, press the "mark" button then go astern for a few seconds followed by a burst of ahead before lowering, hoping that the anchor will hit the sea bed close to your marked position with the boat moving astern more slowly than the chain speed.

There is of course also the issue of what units are available to set the guard radius. My plotter lets me set to multiples of 0.01nm i.e. about 18m, so with 35m of chain out and a distance of 8.5m between bow and GPS aerial, the ideal guard radius (assuming we've somehow managed to correctly place the centre) would be 43.5m. In practice I can choose 36m or 54m. The former would give nuisance alarms so I would choose the latter, accepting that a drag of 10m or more would be needed to trigger the alarm.

 

[Bosun Higgs]

I think a GPS based alarm will cover most situations, but it needs to be a flexibile setup to cope with all of the possible scenarios.

Last weekend we anchored on a quiet night in a well known solent anchorage with reasonable holding and good shelter, but a lot of relatively nearby boats lying to either their own anchors or to laid moorings. The nearest boats were a little too close for real overnight comfort, even with settled weather... an unusual swing could have made things a bit tight.

Consequently I marked the anchor position, and also set a 3/4 scope alarm centered on a position between the boat and the anchor. This obviously went off whenever we had a major swing. This allowed me to get up and eyeball the situation each time we swung, confirm distances to everyone else, and reset the alarm based on the new position.

After four or five swings in the first half of the night (based on a combination of current leaving/entering the anchorage in two ways at different points in the tide, and the onset of the land breeze) I had still not seen any movement on our anchor and none of our neighbours had ever been close enough to be of concern. So I reverted to a more liberal watch centered on the anchor itself and enjoyed the rest of my night's sleep.

Regards

Mike

Four or five sleep disruptions? Why not simply put out your fenders? If you touch another boat you arent going to do it hard in the weather you describe.

 

[supra30]

Four or five sleep disruptions? Why not simply put out your fenders? If you touch another boat you arent going to do it hard in the weather you describe.

I didn't hit the sack until after the first two. As for fendering... if things had looked like there could be a need for that, I'd have upped sticks and gone to anchor outside ;-)