When to Set a Stern Anchor?

[Gone2long]

Originally Posted by coolboat30

Years ago I agreed to crew on a friend's 26 ft fixed keel sloop for a two week island hopping trip out of Puerto Escondido in Baja California. Neither of us were very experienced. The first night out he decided to anchor bow and stern for reasons i didn't fully understand since there was plenty of room to swing. I worried about not being able to swing into the wind if it changed. We awoke at night when a small, local, violent squall (chubasco) hit. Before we had a chance to do hardly anything, the boat was pushed onto the rocks and holed. Within 24 hours one entire side was eaten away and the boat was a total loss. I have always believed that having two anchors out was the problem. The wind hid us abeam and neither one could hold a proper set.

Thanks,

I appreciate you sharing this anecdote about how bad it could be, taking the wind on the beam w. an anchor stern and aft.

Lots of folks up thread have made the point, but a scary story does help to reinforce it and show how bad things can get.

Of course, there could have been lots of intervening circumstances and conditions, but good to hear the tale.

Regards,

G2L

G2L

[Monkeywrench]

Originally Posted by noelex 77

As the wind increases, the chain loses most of its catenary. It is important to add some stretch to the system and a reasonably long (think 10m+) nylon snubber is the best way to do this. In mild winds a short snubber is fine.

Without some elasticity in the system the peak loads are directly transferred to the anchor. The snubber reduces the peak loads considerably.

There was a recent test in Practical Sailor that showed in strong wind the maximium force with a decent snubber was about 1/4 that of all chain with no snubber.

Here is a theoretical analysis:
Rode - Dynamic Behavior

Yes many rookys make this mistake. And usually folks don't have multiple snubers for different conditions. Longer is always better. So I think these rookys in the video dodged the bullet. An Oyster is a very nice boat to risk.

[kas_1611]

In their defence, and mine, snubbers is not something many training places discuss in much detail (if at all). In fact anchoring is not a subject covered in a great amount of detail either (although the school I did my RYA Day Skipper at were very good at anchoring).

Much of my knowledge of anchoring has come from experience and from the shared wisdom of people like Noelex and Mermaid, along with others who have taken the time to discuss the subject in forums like this.

Until Noelex said he used a 13m snubber from the stern cleats I'd never considered using one that long or that my bridled snubber might be considered short, even with the compensator built into it. We all live and learn

Keiron

[hamburking]

Originally Posted by Monkeywrench

Yes many rookys make this mistake. And usually folks don't have multiple snubers for different conditions. Longer is always better.

The same is true of dock lines. So often I see lines tied practically cleat to cleat, with only inches of line. The boat cleat almost always fails due to the huge, unnecessary forces.

[Dockhead]

Originally Posted by Rustic Charm

The time I have double anchored I used just one rode, not two. Thought I guess you could call it a rode from the first anchor to the second anchor of 3 meters. But, whether these get tangled is really not a hassle as the entire lot comes up.

I guess the problem I could face one day is if one anchor get's snagged, Ill loose both of them

That's called "tandem anchoring", and presents its own set of problems. Particularly, getting both anchors well set, but also, it only works in one direction, so what happens when the wind shifts?

Here is what Peter Smith says about it:

"There is one point that should be strongly emphasized, and that is the fact that any multiple anchor rig introduces a complexity to an anchoring set-up that is undesirable. Your primary anchor should be sized to be good enough on its own for most all situations – if it is not, reconsider your choice of that anchor. Tandem anchoring is for extreme situations, in which a single anchor large enough alone would not be practical for daily use.

"Let’s pause to reiterate this. It is a mistake to think to tandem anchor regularly. You must have a primary anchor of a good size and type for your boat. If not, get one."

Two to Tandem: Maximizing Holding Power by Tandem Anchoring

The article is really interesting and is worth reading. Peter Smith, of course, is the inventor of the Rocna anchor.

The inventor of the Spade anchor has similar views on tandem anchoring:

“Attaching two anchors to one rode, known as tandem anchoring, should be avoided.

“The double approach attaches a second anchor with around 15′ of chain in front of the first anchor. I personally almost lost my boat trying out this idea. At the time, my first anchor dragged. Needless to say, it was an old generation model, so I decided to try something new. I added a smaller anchor in front of the large one. This worsened the holding power as opposed to doubling it, drifting swiftly on the smaller anchor while the larger one couldn’t grip at all.

“When an anchor has dragged, a trench formed behind it and this quickly backfilled with loose un-compacted sand. These areas can be still visible after several tides and may explain why some popular anchorages are criss-crossed with patches of poor holding. Then, if the most proximal anchor set, they are very good chances that the [far] anchor will fall down in this loose bottom, with, as a consequence, a poor holding!

“I have done a series of approximately 70 tandem anchorages in the clear waters of the Med, diving on nearly all of them. In 62% of the cases, only one anchor was set. During bad weather, you will not have the possibility to dive to check your anchors, and you only have to ‘trust’ your anchors, which is what I call ‘the Russian Roulette’ anchoring.

“At first, I tried to attach the smallest flat anchor (a 16 kg Brittany) with 5 meters of chain to the hole at the back of the shank of the CQR (20 kg), and I noticed that it will more or less change the equilibrium of the CQR.

“Then I move the five meters chain and attach it at the shackle of the CQR (the extremity of the main chain) but I didn’t notice any difference.”


Cited in Smith's article.

[Dockhead]

Originally Posted by noelex 77

As the wind increases, the chain loses most of its catenary. It is important to add some stretch to the system and a reasonably long (think 10m+) nylon snubber is the best way to do this. In mild winds a short snubber is fine.

Without some elasticity in the system the peak loads are directly transferred to the anchor. The snubber reduces the peak loads considerably.

There was a recent test in Practical Sailor that showed in strong wind the maximium force with a decent snubber was about 1/4 that of all chain with no snubber.

Here is a theoretical analysis:
Rode - Dynamic Behavior

Some eccentric on this Forum argued, a few years ago, that you don't need a snubber at all with heavy chain.

I tried it and realized that indeed, with 50 meters or more of 12mm chain out, it takes pretty strong conditions to get the catenary out.

You can clearly feel whether there's a problem or not -- there's no mistaking the moment when the catenary comes out -- wham!

So nowadays if I'm in good shelter and wind is less than 20 knots, and if I'm staying on board, I don't even bother.


But yes, if you're going to use a snubber, it should be stretchy enough.

In order to be stretchy AND strong (I think at least 20% - 25% of the strength of the rest of the ground tackle), it must be long -- at least 10 meters.

In light conditions, I used to use a lighter, shorter snubber, but now I realize it was never doing anything, anyway, and have repurposed the bit of rope I used to use.

[Cadence]

Originally Posted by Rustic Charm

The time I have double anchored I used just one rode, not two. Thought I guess you could call it a rode from the first anchor to the second anchor of 3 meters. But, whether these get tangled is really not a hassle as the entire lot comes up.

I guess the problem I could face one day is if one anchor get's snagged, Ill loose both of them

If someone it so possessed to set two anchors that would appear to be the way.
Two independent rodes is ridiculous in my humble opinion.
Thanks, sounds like a great idea for soft bottom.

[malbert73]

Originally Posted by noelex 77

My snubber is attached to one of the stern cleats. It passes over the second bow roller extending a metre or so (a lot more when it stretches), where it is attached to the chain with a soft shackle.



I also have a couple of soft shackles that are used as "blocks" or fairleads to keep the snubber away from anything that will cause chafe.



The length is about 13m.

Is there any reason to do this in deep water or where bottom isn't abrasive (i.e. Easier to just rig 30 feet of snubber from bow to chain, right?)


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[Don C L]

I recall in the old days, tandem anchoring was considered the preferred method for a hurricane or some other extreme, one-way, situation only.

[a64pilot]

I had never considered using the stern cleat for attaching a snubber, I need to look and see if that is an option on my boat, I don't know what may be inline or may chafe etc.

[Hudson Force]

I had to go back and review the video of the Oyster anchored in the 35-40 kt wind with the short snubber again. I did note that the waves are more than the mere "ripples" that I had said, but the Oyster is not hobby-horsing or lunging in this, no more than one foot, state. Although the snubber is short, there is no instance in the film where the snubber coiled on the added rubber shock absorber is ever near full extension. There is no indication in the film that the boat is experiencing any shock loaded effects. We are not informed about the size of anchor, type of anchor, rode length to depth ratio, bottom condition, anchor drag monitoring plan or the proximity of a lee shore, but everything looks pretty peaceful to me.

I have to disagree with those that feel this crew was putting the Oyster at risk by what is disclosed in the video. This all looks fairly calm and well secured to me.

[noelex 77]

Originally Posted by malbert73

Is there any reason to do this in deep water or where bottom isn't abrasive (i.e. Easier to just rig 30 feet of snubber from bow to chain, right?)

Rigging a long snubber from the bow is fine and is what most boats do. In light wind the snubber may rub on the bottom. This is not a big problem, but there is potential chafe, the snubber can get grubby, and if you use a chain hook it can fall off if it is not the type that is secured.

In light wind a long snubber is not needed, so many boats rig a short bow snubber (just to take the load off the windlass). This can be lengthened if stronger wind arrives. If you simply let out more snubber and chain it has the added bonus of letting out a bit more scope in the stronger conditions.

Unfortunately, a long snubber from the bow can occasionally wrap or spiral around the chain.

A snubber rigged from the stern is not viable on many boats. There is just not a practical path from the stern to the bow. It is also another deck line to potentially trip over. Some lead a snubber rigged from the stern forward via the stanchion bases, but I wonder if these are strong enough? Has anyone used this system in strong winds? The stanchion bases only slightly alter the angle of the snubber, so have only a fraction of the load. perhaps they are adequately strong.

The advantages of a snubber rigged from the stern is that it easy to always use a long snubber. While this is overkill for most situations, it saves having to get on deck and lengthen the snubber if conditions unexpectedly deteriorate. Unexpected strong wind always arrives at 2am .

The second significant advantage of a snubber rigged from the stern is that it easier to lengthen the rode (increasing the scope) even if a lot mere rode is needed.

With a long bow snubber, if conditions deteriorate unexpectedly, and you decide more scope is needed, letting out more chain is not always easy. Normally you need to retrieve 10m of chain to get to the chain snubber connection. This can be very difficult in strong conditions. The foredeck is a wet, uncomfortable and dangerous place. The engine will struggle to make headway into the wind and it is very hard not to impose significant snatch loads during the transition period. Scary.

There are alternatives with a bow snubber. You can extend the snubber. This need not be nylon rope but a long length of rope is a pain, especially if it wraps around the chain. You can simply release the snubber and attach another when more chain has been let out. However when you need to retrieve this you need need to be careful the rope cannot be caught around the prop. This is an added problem especially if the boat is dragging.

A snubber rigged from the stern has advantages in these extreme conditions. It will be attached to the rode just over the bow (it can even be inboard). More chain can be let out reasonably easily without having to pull in a lot of chain to disconnect the snubber. Easy and reasonably safe .

In short, a stern rigged snubber is superior if it is practical. If not a bow rigged snubber is fine, but make sure it long (10m+) if conditions are severe.

[Dockhead]

Originally Posted by noelex 77

Rigging a long snubber from the bow is fine and is what most boats do. In light wind the snubber may rub on the bottom. This is not a big problem, but there is potential chafe, the snubber can get grubby, and if you use a chain hook it can fall off if it is not the type that is secured.

In light wind a long snubber is not needed, so many boats rig a short bow snubber (just to take the load off the windlass). This can be lengthened if stronger wind arrives. If you simply let out more snubber and chain it has the added bonus of letting out a bit more scope in the stronger conditions.

Unfortunately, a long snubber from the bow can occasionally wrap or spiral around the chain.

A snubber rigged from the stern is not viable on many boats. There is just not a practical path from the stern to the bow. It is also another deck line to potentially trip over. Some lead a snubber rigged from the stern forward via the stanchion bases, but I wonder if these are strong enough? Has anyone used this system in strong winds? The stanchion bases only slightly alter the angle of the snubber, so have only a fraction of the load. perhaps they are adequately strong.

The advantages of a snubber rigged from the stern is that it easy to always use a long snubber. While this is overkill for most situations, it saves having to get on deck and lengthen the snubber if conditions unexpectedly deteriorate. Unexpected strong wind always arrives at 2am .

The second significant advantage of a snubber rigged from the stern is that it easier to lengthen the rode (increasing the scope) even if a lot mere rode is needed.

With a long bow snubber, if conditions deteriorate unexpectedly, and you decide more scope is needed, letting out more chain is not always easy. Normally you need to retrieve 10m of chain to get to the chain snubber connection. This can be very difficult in strong conditions. The foredeck is a wet, uncomfortable and dangerous place. The engine will struggle to make headway into the wind and it is very hard not to impose significant snatch loads during the transition period. Scary.

There are alternatives with a bow snubber. You can extend the snubber. This need not be nylon rope but a long length of rope is a pain, especially if it wraps around the chain. You can simply release the snubber and attach another when more chain has been let out. However when you need to retrieve this you need need to be careful the rope cannot be caught around the prop. This is an added problem especially if the boat is dragging.

A snubber rigged from the stern has advantages in these extreme conditions. It will be attached to the rode just over the bow (it can even be inboard). More chain can be let out reasonably easily without having to pull in a lot of chain to disconnect the snubber. Easy and safe .

In short, a stern rigged snubber is superior if it is practical. If not a bow rigged snubber is fine, but make sure it long (10m+) if conditions are severe.

I like your long snubber arrangement and have imitated your technique.

But I was a bit alarmed by the phrase "short snubber to take the load off the windlass"

As the only means of belaying the chain ahead of the windlass? I hope not. I know you would never do this, but I see people regularly with nothing holding the chain to the boat but a snubber. Which, in order to be effective as a snubber, is generally 3 to 4 times weaker than the chain. Or more likely even weaker after months or years of service stretching and chafing as snubbers do.

A chain is only as strong as its weakest link - don't reduce the strength of your ground tackle to this. The method of attaching the chain to the boat should be as strong as the chain. It's a different function from snubbing.

/rant




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[noelex 77]

Originally Posted by Dockhead

So nowadays if I'm in good shelter and wind is less than 20 knots, and if I'm staying on board, I don't even bother.

Yes, that is fine. At 20 knots there is plenty of catenary to provide stretch. A snubber is not necessary for holding.

For those boats that don't have a chain stopper (I seem to recall you have one) I think a short snubber to take the load off the windlass, and preserve the bearings, even in these light conditions is a good idea, especially while setting the anchor. I think giving mechanical components as easy a life as possible is a good idea, but it is difficult to know in cases like this if it makes any practical difference.

Personally, I generally use a long snubber even in settled conditions. It means I don't have to sleep with one ear listening for deteriorating conditions.

If you can set up a snubber rigged from the stern (this is not practical on many boats) there is little effort involved in deploying the snubber and no difference between using a long or short snubber.

Systems like this that use best practice as a routine are worth employing where possible. The sea is full of surprises .

[noelex 77]

Originally Posted by Dockhead

As the only means of belaying the chain ahead of the windlass? I hope not. I know you would never do this, but I see people regularly with nothing holding the chain to the boat but a snubber.

Yes, I agree. Snubbers do break. I have broken many. To work properly snubbers need a lot of stretch so they are working close to their limit. The chain needs to be secured as a back up. This can be a chain stopper, a short strong "snubber" or a hook/shackle arrangement.

In addition, in severe conditions it is worth considering having a back up second long snubber.

Snubbers break with an enormous bang that would wake the dead, so you will be generally aware of the failure, but it takes some time to rig an additional snubber. Loosing the stretch is bad enough but placing this load on the directly on the gypsy is a recipe for dragging with a broken windlass.