Anchor watch - electronic or sit on deck?

[pagoda]

Having arrived at Craighouse on Jura on Saturday - missing the last mooring, we anchored in about 4m of water slightly NE of the moorings. There are various warnings about the poor holding here - due to weed, so I let out 30m of 8mm chain on a Bruce anchor (35 ft boat). The transits looked fine as we went to bed, but it was ramping up to a 5 with squalls, so I set a 15m alarm on my hand held GPS. It went off twice during the night, but I was able to see nothing dreadfull happening -a modest arc as the wind shifted- so back to sleep Ok.
What'e the collective wisdom on either depth alarms or proximity - GPS alarms?
20m might have ensured no alerts at all , but had we slipped astern - there was another boat came in behind us- and 20m could have been a touch exciting to find in the morning?

thanks, Graeme

 

[snowleopard]

I'd never sit up all night in less than a gale but I always set the GPS alarm and sometimes leave the depth alarm on as well.

A few weeks ago I posted a poll on this subject and was amazed at the number of people who had a GPS alarm but didn't use it, trusting to their favourite anchor and confidence in their ability to waken at a change of motion.

 

[pvb]

Probably using both depth and GPS alarms is the optimum answer, but the precision of GPS alarms is very appealing.

 

[prv]

I have done old-fashioned anchor watches on a yacht, but only in the Army.

I've also done anchor watch on a square-rigger, where they tend to trace the picture on the radar screen with a grease-pencil and you call the duty officer if the picture drifts away from the lines.

My GPS is too quiet to wake me.

My anchor is the much-maligned CQR, but it is pretty big for the size of the boat. I have a lot of chain and I'm generally anchoring in forgiving Solent mud. I sleep easy.

Pete

 

[Danny_Labrador]

GPS

I'd never sit up all night in less than a gale but I always set the GPS alarm and sometimes leave the depth alarm on as well.

Isn't the problem with GPS that with a wind direction shift, (not a drag) the radius you sweep sets off the alarm when in fact all is well and normal ?

 

[PhilipH]

Depends on weather and location. If calm and plenty of swinging room then don't bother with any alarms, but in F4/F5 and upwards then anchor alarm (GPS) - depth alarm only useful if there's a significant change in depth within similar range as that of anchor alarm.

 

[shmoo]

First, make sure the hook really is in. The alarm is for exceptions so let's try to make it so!
GPS set to twice the scope (d = 2r) plus 10m should avoid false alarms due to swinging. I usually set my phone alarm for swinging time anyway, just to put my head out for a look.

 

[bbg]

Isn't the problem with GPS that with a wind direction shift, (not a drag) the radius you sweep sets off the alarm when in fact all is well and normal ?

You could resolve that by setting the alarm when you drop the anchor (or after the anchor is set, motoring up until the boat is above the anchor again) and setting an alarm that is consistent with the amount of rode out. That way the center of the alarm zone is over the anchor, and you can swing anywhere in the radius of the rode.
Swing outside the radius of the rode (i.e. drag) and the alarm goes off.

 

[Poignard]

I usually set my phone alarm for swinging time anyway, just to put my head out for a look.

Yes I do that.

 

[DaveS]

GPS Anchor Alarm

Certainly agree about the poor holding at Craighouse. It's the only place I've ever seriously dragged despite having out huge scope. The problem seems to be that you pick up a ball of kelp that stops the anchor digging in. Once the stem(s) attached to the bottom break you're away.

I read that the ideal time to set the anchor alarm is just as the anchor is lowered, so that the guard radius can be set to just greater than scope + boat length, rather than twice that to allow for 180 deg shift. Actually remembering to press the right buttons at the right time is another matter however. Despite good intentions I forgot on every occasion on this year's summer trip!

 

[agurney]

Having arrived at Craighouse on Jura on Saturday - missing the last mooring, we anchored in about 4m of water slightly NE of the moorings. There are various warnings about the poor holding here - due to weed, so I let out 30m of 8mm chain on a Bruce anchor (35 ft boat). The transits looked fine as we went to bed, but it was ramping up to a 5 with squalls, so I set a 15m alarm on my hand held GPS. It went off twice during the night, but I was able to see nothing dreadfull happening -a modest arc as the wind shifted- so back to sleep Ok.
What'e the collective wisdom on either depth alarms or proximity - GPS alarms?
20m might have ensured no alerts at all , but had we slipped astern - there was another boat came in behind us- and 20m could have been a touch exciting to find in the morning?

thanks, Graeme

Every time there's dip in GPS reception, whether for lack of satellites in optimal positions or RF effects, you're likely to end up with a false alarm.

BTW why choose a busy anchorage with poor holding? Lowlandman's Bay a mile or so to the north (http://sailing.agurney.com/list-of-anchorages/lowlandmans-bay) is far quieter, has better shelter and holding, and avoids that horrible swell that you get in Craighouse.



Alisdair

 

[maxi77]

I think like everything else it is horses for courses. GPS and depth alarms can be good if they will tell you in time to take action before disaster happens, if they don't then you really need to take other precautions including an on deck watch.

I ca remember once in a submarine moored between two bouys in Loch Goil spending the whole night a full sea going watches during a nasty gale because if our moorings went we needed full power instantly to avoid hitting the rocks. The usual anchor watch would have been totaly inadequate.

 

[snowleopard]

I've also done anchor watch on a square-rigger, where they tend to trace the picture on the radar screen with a grease-pencil and you call the duty officer if the picture drifts away from the lines.

Me too. Which one?

 

[noelex]

Every time there's dip in GPS reception, whether for lack of satellites in optimal positions or RF effects, you're likely to end up with a false alarm.



Alisdair

With the number of gps satellites available this is very rare cause of false alarms. With EGNOS enabled I cannot remember the last false alarm due to this and my anchor alarm is on 24/7 (when not sailing to a new destination).

 

[Robin]

Have a decent sized and decent design anchor that you trust (sorry but the Bruce or more likely a Chinese copy of one is not one of my favourites), plenty of chain and dig the anchor in under power, starting gently and increasing gradually to lean hard on it all with near full revs astern. If it will stand that treatment on arrival it should stand a little F4/5 and then some whilst you sleep, if it won't then try again somewhere else. Once the anchor is set, go to bed and relax! A GPS alarm will drive you nuts when sooner or later it will jump position or the boat will swing enough to set it off. Depth alarm only works if there is sufficient change of depth close outside of position A (and when tide rise and fall is factored in). In 4m of water which is relatively shallow you need more than the usual 3-5 times depth out, chain works better on the seabed than it does in the anchor locker. Use a nylon snubber line preferably with a stretchy rubber mooring compensator wound in it, between the chain and a foredeck cleat and with the chain in a slack loop below it. The snubber will stop the 'snatch' loads from jerking the anchor out as the boat swings in the gusts.

The only other options for a decent kip is a better anchorage or a handy marina because if you need a beeper you will not sleep well listening for it!

All IMHO, but we never drag..

 

[Bosun Higgs]

In a situation which requires an anchor watch I always get up and look at the transits. I wouldnt sleep if I didnt do so.

The key is a good anchor, something better than a Bruce which is consistently near the bottom of every anchor test. You might disregard one or two tests but not every one.

 

[pagoda]

Thanks all,

We didn't drag at all as it happened - though there was the most hideous ball of kelp and bootlace weed came up with the anchor eventually. The bay at Craighouse is pretty shallow- but with a small tidal range thank goodness - or it would be a hopeless place to visit. A 4-spreader yacht turned up on Sunday and was confined to west of Pladda due to water depth.. we had about 75m to reach the pier/pontoon.
I reckon I'll try about 75% of scope for a GPS alarm next - to see how that works out.
Comments were much appreciated.

Graeme

 

[ColdFusion]

Have a decent sized and decent design anchor that you trust (sorry but the Bruce or more likely a Chinese copy of one is not one of my favourites), plenty of chain and dig the anchor in under power, starting gently and increasing gradually to lean hard on it all with near full revs astern. If it will stand that treatment on arrival it should stand a little F4/5 and then some whilst you sleep, if it won't then try again somewhere else. Once the anchor is set, go to bed and relax! A GPS alarm will drive you nuts when sooner or later it will jump position or the boat will swing enough to set it off. Depth alarm only works if there is sufficient change of depth close outside of position A (and when tide rise and fall is factored in). In 4m of water which is relatively shallow you need more than the usual 3-5 times depth out, chain works better on the seabed than it does in the anchor locker. Use a nylon snubber line preferably with a stretchy rubber mooring compensator wound in it, between the chain and a foredeck cleat and with the chain in a slack loop below it. The snubber will stop the 'snatch' loads from jerking the anchor out as the boat swings in the gusts.

The only other options for a decent kip is a better anchorage or a handy marina because if you need a beeper you will not sleep well listening for it!

All IMHO, but we never drag..

All good stuff. The only thing I'd add is to also slide a chum*/angel** down the anchor chain until it's a couple of metres off the bottom. This will also help to reduce snatch loads on the anchor.

* not your best friend
** not your guardian angel

 

[agurney]

With the number of gps satellites available this is very rare cause of false alarms. With EGNOS enabled I cannot remember the last false alarm due to this and my anchor alarm is on 24/7 (when not sailing to a new destination).

It isn't everyone that has an EGNOS enabled GPS.

 

[pagoda]

It isn't everyone that has an EGNOS enabled GPS.

I discovered my older Raymarine plotter happily uses the new Egnos satellites in the same way it was expecting to use the WAAS function which was not originally available in Europe.
I reckon it is more available than expected - just try enabling WAAS if you can find the menu option!

Graeme