Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 17-03-2016, 07:08   #106
Registered User

Join Date: Sep 2010
Posts: 844
Images: 1
On the Danger of an Unnecessary Stern Anchor

Quote:
Originally Posted by coolboat30 View Post
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
__________________

__________________
Gone2long is offline   Reply With Quote
Old 17-03-2016, 09:27   #107
Registered User

Join Date: Feb 2016
Posts: 8
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by noelex 77 View Post
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.
__________________

__________________
Monkeywrench is offline   Reply With Quote
Old 17-03-2016, 09:45   #108
Registered User

Join Date: Dec 2013
Location: Rogoznica, Croatia
Boat: Bavaria Cruiser 40
Posts: 619
Images: 16
Re: When to Set a Stern Anchor?

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
__________________
kas_1611 is offline   Reply With Quote
Old 17-03-2016, 10:22   #109
Registered User
 
hamburking's Avatar

Join Date: Feb 2013
Location: Kingston Ont Canada
Boat: Looking for my next boat!
Posts: 2,149
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by Monkeywrench View Post
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.
__________________
hamburking is offline   Reply With Quote
Old 17-03-2016, 10:30   #110
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by Rustic Charm View Post
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.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 17-03-2016, 10:44   #111
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by noelex 77 View Post
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.
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 17-03-2016, 10:48   #112
Registered User
 
Cadence's Avatar

Join Date: Dec 2008
Location: SC
Boat: None,build the one shown of glass, had many from 6' to 48'.
Posts: 6,063
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by Rustic Charm View Post
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.
__________________
Cadence is offline   Reply With Quote
Old 17-03-2016, 12:35   #113
Registered User
 
malbert73's Avatar

Join Date: Jun 2008
Boat: Tartan 40
Posts: 1,032
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by noelex 77 View Post
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?)


Sent from my iPhone using Cruisers Sailing Forum
__________________
malbert73 is offline   Reply With Quote
Old 17-03-2016, 13:04   #114
Moderator
 
Don C L's Avatar

Join Date: Sep 2014
Location: Channel Islands, CA
Boat: 1962 Columbia 29 MK 1 #37
Posts: 4,394
Images: 34
Re: When to Set a Stern Anchor?

I recall in the old days, tandem anchoring was considered the preferred method for a hurricane or some other extreme, one-way, situation only.
__________________
DL
Pythagoras
1962 Columbia 29 MKI #37
Don C L is offline   Reply With Quote
Old 17-03-2016, 13:18   #115
Moderator
 
a64pilot's Avatar

Cruisers Forum Supporter

Join Date: Oct 2013
Location: Albany Ga.
Boat: Island Packet 38
Posts: 17,056
Re: When to Set a Stern Anchor?

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.
__________________
a64pilot is offline   Reply With Quote
Old 17-03-2016, 14:39   #116
Moderator
 
Hudson Force's Avatar

Cruisers Forum Supporter

Join Date: Nov 2008
Location: Lived aboard & cruised for 45 years,- now on a chair in my walk-in closet.
Boat: Morgan OI 413 1973 - Aythya
Posts: 7,894
Images: 1
Re: When to Set a Stern Anchor?

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.
__________________
Take care and joy, Aythya crew
Hudson Force is offline   Reply With Quote
Old 18-03-2016, 02:24   #117
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,619
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by malbert73 View Post
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.
__________________
noelex 77 is offline   Reply With Quote
Old 18-03-2016, 03:12   #118
Moderator
 
Dockhead's Avatar

Cruisers Forum Supporter

Join Date: Mar 2009
Location: Cowes (Winter), Baltic (Summer) (the boat!); somewhere in the air (me!)
Boat: Cutter-Rigged Moody 54
Posts: 19,750
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by noelex 77 View Post
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




Sent from my D6633 using Cruisers Sailing Forum mobile app
__________________
"Parce que je suis heureux en mer, et peut-Ítre pour sauver mon ame. . . "
Dockhead is offline   Reply With Quote
Old 18-03-2016, 03:13   #119
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,619
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by Dockhead View Post
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 is offline   Reply With Quote
Old 18-03-2016, 04:24   #120
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Location: Living on dirt waiting for our new yacht to be built.
Boat: Half built Bestevaer.
Posts: 10,619
Re: When to Set a Stern Anchor?

Quote:
Originally Posted by Dockhead View Post
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.
__________________

__________________
noelex 77 is offline   Reply With Quote
Reply

Tags
anchor

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Why Would Cabo Rico's Stern Set Low in Water? Sea_Nymph Construction, Maintenance & Refit 24 15-08-2015 01:28
Stern Anchor Roller or Fairlead Dockhead Anchoring & Mooring 20 13-03-2011 04:11
Stern Anchor and Sugar Scoops ? Sabbatical II Anchoring & Mooring 8 22-04-2010 14:50
Stern Anchor Fitting for an 11m Catamaran rivonia Multihull Sailboats 2 16-10-2009 05:47
Stern Anchor Line Reel Tspringer Construction, Maintenance & Refit 1 16-05-2008 02:38



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:26.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.