Anchoring

[SaltyC]

I

I know what you mean.

It used to be so easy before they invented online forums.

AND new generation anchors! CQR, Danforth and Fisherman. Yet don't remember any more problems with dragging anchors than people have now.

I will exclude Mevagissey in a SE gale overnight, for a 12 year old that was SCARY!

 

[lustyd]

It has to reasonable holding. All bets are off in, for example, rock substrate.
People overestimate the force on the anchor from current. This article gives a good analysis:

Forces
A quote from this article :
"We can see a 6 kt current - which is unlikely in most anchoring situations - has about the same effect as a 20 kt wind." (This is for a yacht with a 10m waterline).

The force on the anchor system from a 4kt current is only about 30 daN (about 31 kilogram-force).

I just don't believe that site at all. I've seen my 11m boat in a 6kt current and a 20kt wind and can assure you the 6kt tide had a much more rapid effect which equates directly to greater force.

 

[noelex]

The bottom line is that you do not want an anchor design that breaks out with a change in the direction of pull, whether from wind or current.

Some anchor designs develop a very high list as they shuffle in response to a change in direction of pull. often these designs never set well. There is a greater risk that the anchor will break out completely. If this happens the anchor has to try and set while moving rapidly. A difficult job for any anchor.

 

[ylop]

I use an anchor app. I’ve tried a few. They do give false positives, but I’d rather that than not go off - worth considering that when I set it at the helm I am about 8m aft of where my phone sits when I am asleep, plus some gps error and that’s probably a 12+m diameter circle before the boat has even moved around! Once it’s gone off - no matter how much I know it’s just an error I can’t sleep properly and tend to move to the saloon where I can more quickly respond / investigate future alarms.

I’m sure there is a slick routine for setting it on the foredeck, just as the anchor starts to dig in, so that you can just add the scope and a bit for boat length and be Confident in the radius but i am instructing a crew, making sure I am ready to go backwards, watching for other people, etc so often only set the anchor alarm after the boat is stopped and have to guess the true location of the anchor. (I’m a bit surprised the apps don’t attempt to learn/estimate it).

 

[noelex]

worth considering that when I set it at the helm I am about 8m aft of where my phone sits when I am asleep, plus some gps error

This is an astute observation. An anchor alarm needs to centred over the anchor, not the position of the GPS aerial when the anchor is dropped. Many people get these basics wrong.

Modern GPS units are very accurate. If you centre the alarm over the anchor you are very unlikely to every have any false positive alarms. Many set the anchor alarm incorrectly and then become frustrated by the false alarms. This is a pity.

It is a great tool when set correctly.

 

[dunedin]

One thing that does cause some confusion for novices - and often amusement for spectators - is the people who remember that they should “pay out the chain going backwards, and use some revs to set the anchor”.
They forget, or don’t realise, that this is shorthand for “pay out the chain going GENTLY backwards and only then LATER, once the anchor has gripped, check that it is secure by using some revs to set the anchor”

Much is the fun (if safely away from the line of fire) watching a (often charter) boat hurtle into an anchorage at 7 knots, start dropping the anchor as the skipper hits reverse with a vengeance, then disappear back out of the anchorage reversing at 5 knots. When 1/4 mile or so outside the anchorage, lift chain and repeat two more times, before going elsewhere or picking up anything that looks vaguely like a mooring buoy (woe if this is your anchor trip buoy]

One thing not seen mentioned here. We put on the “lunch hook” (a short rope snubber) to take the strain off the windlass before reversing to set the anchor. Didn’t used to do this but after 500 or so iterations the bearings were rather poorly.
Overnight we have a long stretchy snubber with hook, plus the short lunch hook in case the snubber parts or the hook comes off.

 

[Baggywrinkle]

This is an astute observation. An anchor alarm needs to centred over the anchor, not the position of the GPS aerial when the anchor is dropped. Many people get these basics wrong.

Modern GPS units are very accurate. If you centre the alarm over the anchor you are very unlikely to every have any false positive alarms. Many set the anchor alarm incorrectly and then become frustrated by the false alarms. This is a pity.

It is a great tool when set correctly.

I set the anchor alarm to cover the track of where the boat is moving when I go to bed. It wakes me up if the wind shifts and pushes me out of this area.

Where I cruise this is usually the first sign of a localised thunderstorm ... and I like to be up and observant as the plethora of charter boats start swinging about as the wind builds. This has saved my bacon on a number of occasions when boats with half cut or half asleep crews start to tangle and drag in overcrowded anchorages. I'll set the alarm with more space if the anchorage is empty.

 

[Baggywrinkle]

One thing that does cause some confusion for novices - and often amusement for spectators - is the people who remember that they should “pay out the chain going backwards, and use some revs to set the anchor”.
They forget, or don’t realise, that this is shorthand for “pay out the chain going GENTLY backwards and only then LATER, once the anchor has gripped, check that it is secure by using some revs to set the anchor”

Much is the fun (if safely away from the line of fire) watching a (often charter) boat hurtle into an anchorage at 7 knots, start dropping the anchor as the skipper hits reverse with a vengeance, then disappear back out of the anchorage reversing at 5 knots. When 1/4 mile or so outside the anchorage, lift chain and repeat two more times, before going elsewhere or picking up anything that looks vaguely like a mooring buoy (woe if this is your anchor trip buoy]

One thing not seen mentioned here. We put on the “lunch hook” (a short rope snubber) to take the strain off the windlass before reversing to set the anchor. Didn’t used to do this but after 500 or so iterations the bearings were rather poorly.
Overnight we have a long stretchy snubber with hook, plus the short lunch hook in case the snubber parts or the hook comes off.

Seen that loads of times .... watching their chain bounce as they skip the anchor over the bottom at 5-6 knots

 

[[2574]]

I avoid jellyfish stings by deploying our 12m nylon snubber on deck. Attached to the chain just after the roller then led back through blocks to either midship or aft cleat. Necessity is the mother of invention……

Oh, as a footnote, show an anchor light and day shape.

 

[noelex]

I set the anchor alarm to cover the track of where the boat is moving when I go to bed. It wakes me up if the wind shifts and pushes me out of this area.

Where I cruise this is usually the first sign of a localised thunderstorm ... and I like to be up and observant as the plethora of charter boats start swinging about as the wind builds. This has saved my bacon on a number of occasions when boats with half cut or half asleep crews start to tangle and drag in overcrowded anchorages. I'll set the alarm with more space if the anchorage is empty.

It is sometimes useful to deliberately set an "anchor" alarm that will alert you if the wind changes direction (rather than if the anchor drags). This setting can be especially useful if there is a hazard in the swing circle.

However, many set their anchor alarm incorrectly. The resulting false alarms give anchor alarms a bad reputation when in reality this is just user error. Modern GPS units are very accurate so false alarms are nearly always an error when setting up the alarm, most commonly not setting the alarm centre over the anchor.

 

[srm]

Life was so much easier when most boat's electronic aids were an echo sounder and a hand held RDF. We anchored, checked the anchor was not dragging with ad hoc transits, and settled down. At dusk looked for a shore light to help confirm position at night, (in many anchorages I used no shore lights were visible), lit the anchor light and later turned in. Having a reliable anchoring system allowed a sound night's sleep.

 

[noelex]

Life was so much easier when most boat's electronic aids were an echo sounder and a hand held RDF. We anchored, checked the anchor was not dragging with ad hoc transits, and settled down. At dusk looked for a shore light to help confirm position at night, (in many anchorages I used no shore lights were visible), lit the anchor light and later turned in. Having a reliable anchoring system allowed a sound night's sleep.

I started cruising before GPS was available, but I do not long for the "good old days". To have an alarm that is always on watch and will signal an alert, if the anchor moves a few meters, even if I am asleep is a modern marvel. It works even in areas with no shore lights, in fog, or even in the many occasions when I am not paying attention to our position.

I agree that an excellent anchoring system is the most important priority for cruising sailors that anchor frequently, but why not supplement this with an electronic alarm that will provide an alert if things go wrong? The cost is minimal (most yachts already have this equipment) as is the power consumption. I don’t understand the resistance.

 

[rib]

I have added Google earth to my method.. Cruising the Turkish coast if anchoring at night in a new anchorage checking where the weedier side of the bay is helps and cuts down the risk of anchoring in weed.. Not % but gives a fighting chance for this solo sailor

 

[Baggywrinkle]

It is sometimes useful to deliberately set an "anchor" alarm that will alert you if the wind changes direction (rather than if the anchor drags). This setting can be especially useful if there is a hazard in the swing circle.

However, many set their anchor alarm incorrectly. The resulting false alarms give anchor alarms a bad reputation when in reality this is just user error. Modern GPS units are very accurate so false alarms are nearly always an error when setting up the alarm, most commonly not setting the alarm centre over the anchor.

I agree that you need to understand what you are using your anchor alarm for, changes in wind direction, dragging, hazards, ... and it is important to geofence the area of interest as accurately as possible while avoiding false alarms.

If only interested in dragging, then a circle centred on the anchor position taking into account amount of chain released makes absolute sense.

If interested in hazards then an area centered on the boat position which excludes the hazard with a margin of error would be the way to go.

If interested in wind shifts or change of tide direction then a track collected over an hour or so can form a good basis for a geofence that will exclude the boats normal movement at its current location and in the prevailing conditions.

.. and then there is the plethora of Smartphone Anchor Alarm apps on the Apple and Android stores.

Users need to be aware that there are a number of caveats with smartphone apps that can affect the position the phone calculates - the Android FusedLocationProviderClient API will return positions that use WiFi RTT, BT, as well as GPS to provide a "more accurate" position than GPS alone. It is also possible for the user or the developer to mess up the Apps location accuracy dependent on how the developer has chosen to use the various Android APIs available, and what permissions the App asks for, or what the user allows in terms of App permissions, or has set in terms of location accuracy.

For example this is a comment from the developer of "Anchor Alarm" on the Android App Store in response to a one-star review ...

Hello, the app uses the location services of your device. This can be GPS and BT/WiFi. Sometimes it helps to disable the "Google location accuracy" (BT/WiFi) in the system settings of your device, because this can introduce location jumps, especially near ports with multiple WiFi points. After disabling, only GPS is used. Contact us for more help.

Anchor Alarm - Apps on Google Play

Basically, a well established Anchor Alarm app with a large user base and a good App Store rating is prefereble IMO to anything more obscure, with either low ratings or low install base - regardless of user interface or extra bells and whistles. User beware and don't rely 100% on the App, use the Alarm function on the Plotter too if available.

 

[johnalison]

I take the usual care when anchoring, but what is really irritating is that all around me I see people anchoring any-old-how, slow, fast, forwards or whatever, and the results of their lack of attention are just as good as mine.

 

[B27]

It has to reasonable holding. All bets are off in, for example, rock substrate.
People overestimate the force on the anchor from current. This article gives a good analysis:

Forces
A quote from this article :
"We can see a 6 kt current - which is unlikely in most anchoring situations - has about the same effect as a 20 kt wind." (This is for a yacht with a 10m waterline).

The force on the anchor system from a 4kt current is only about 30 daN (about 31 kilogram-force).

The force in a given speed of current will depend on a few things, including the waterline length.
My little boat is making waves at 6 knots, a 40ft trimaran isn't.

Also, the drag of the current on the chain is probably quite high?

A current of a few knots can combine with a modest wind to kick up a significant chop.
Waves, even small ones can create a lot of force, if the rode snatches, a great deal of instantaneous force is available.

Even in flat water, I can tell that the load on my mooring increases a lot when a cross wind pushes the boat across the current a little!

Likewise, a 20 knot wind that's swirling down the river is probably a lot more potent than a steady 20 knots bang on the nose.

 

[Roberto]

The force in a given speed of current will depend on a few things, including the waterline length.
My little boat is making waves at 6 knots, a 40ft trimaran isn't.

Also, the drag of the current on the chain is probably quite high?

A current of a few knots can combine with a modest wind to kick up a significant chop.
Waves, even small ones can create a lot of force, if the rode snatches, a great deal of instantaneous force is available.

Even in flat water, I can tell that the load on my mooring increases a lot when a cross wind pushes the boat across the current a little!

Likewise, a 20 knot wind that's swirling down the river is probably a lot more potent than a steady 20 knots bang on the nose.

There is also another factor which is relevant in anchor setting: that XXdaN force is a static load for a hull perfectly aligned with the current. While dropping anchor in a current, if one does not want to end a hundred metres downstream of the intended spot it has to let go the chain quite rapidly. The boat gathers momentum a lot more quickly than if it was pushed by the wind, and when the chain is eventually made fast and the anchor sets the load is huge, easily XXXdaN. I have a 10m LWL boat, there is no way I could hold the chain with my hands when the boat is stopped even with a 2kt current.
I use a short rope strop with a chain hook in these situations, the shrieking sound it makes when the chain goes taut and stops the boat tells a long story

 

[srm]

I agree that an excellent anchoring system is the most important priority for cruising sailors that anchor frequently, but why not supplement this with an electronic alarm that will provide an alert if things go wrong? The cost is minimal (most yachts already have this equipment) as is the power consumption. I don’t understand the resistance.

No resistance, I have a full set of electronic toys that I can play with as and when appropriate. They can make single handed sailing much safer. However, from many years of experience I know that once my anchor is set I will still be in or very close to the same place the next morning with something better than 99.8% probability.

I was simply commenting on the disproportionate number of posts discussing how to or how not to set up an anchor alarm. Is it really so complicated?

 

[noelex]

I know that once my anchor is set I will still be in or very close to the same place the next morning with something better than 99.8% probability.

That 0.2% is a bugger.

I was simply commenting on the disproportionate number of posts discussing how to or how not to set up an anchor alarm. Is it really so complicated?

Setting an anchor alarm that is properly centred on the anchor rather than where the GPS aerial is located is not difficult, but not many people get it right.

 

[srm]

That 0.2% is a bugger.

No, just inconvenient and annoying. However, it was a delivery trip and I only had the lightweight anchor and chain that came with the boat so no great surprise.