Anchoring question

[zboss]

If 95% of cruisers use all chain and in a hurricane all the boats dragged anchor, that’s data that indicates correlation not a causation. I personally dislike it when the one guy in the packed anchorage has to put out 250 feet of rope when everyone else is using 100. If you want to use all rope be my guest but be considerate of everyone else that may want to anchor in the same cove.

[waeshael]

Originally Posted by zboss

If 95% of cruisers use all chain and in a hurricane all the boats dragged anchor, that’s data that indicates correlation not a causation. I personally dislike it when the one guy in the packed anchorage has to put out 250 feet of rope when everyone else is using 100. If you want to use all rope be my guest but be considerate of everyone else that may want to anchor in the same cove.

The length of the rode needed is a function of the water depth and doesn't depend up the type of rode material. A burying anchor works by being slowly sucked under the sand, and requires a particular angle for the rode. For instance a CQR requires a 7 degree slope. This means that the length of the rode must be about 8 times the height from the bowsprit to the sand. Any steeper angle and the CQR begins to pull out and not slide deeper. Whether you use chain to do this or nylon makes hardly any difference because under load when the wind blows the chain will be straight like a rod and there is no benefit from its weight - it has no catenary. Anchored in 20 feet of water with 5 feet from the LWL to the bow requires a rode length of 8 x 25 = 200 feet. Now, since you have no idea what type of anchor your neighbor is using and his rode length, you have to make sure you are well clear, because if he has miscalculated his anchoring system it will drag in a blow.
Now you can reduce rode length with special anchors that bury at higher rode angles, such as a fortress.
But generally speaking in 20 feet of water you should see a 200 foot rode.
Now if the wind gets up and the waves get high, the angle will be reduced and the anchor might be pulled upwards rather than down, so in a blow you have to let out more rode, or allow for this increase in height by anchoring in a shallower spot to begin with.
You might test this yourself: When leaving an anchorage try to pull the anchor out of the sand using the windlass and see if it slides. If it is solid walk the boat forwards and try again. Find the point where the anchor breaks free, and mark the rode where it comes into the windlass with a red felt pen or a piece of duck tape. Then haul in the anchor and when you get a chance measure the length of the rode where the anchor broke out, then calculate the angle of the road at that point. You will begin to see the relationship between rode angle and the angle that causes the anchor to release from the sand. The holding power of a CQR anchor and most burying anchors depends upon the rode angle while the system is under tension when the wind blows. For burying anchors an angle of 10 degrees reduces its holding power significantly.
You must understand that a burying anchor must drag in order to develop its holding power which depends only upon the weight of sand above the flukes that has to be moved out of the way to allow the anchor to surface. Buried down two feet even a small CQR will hold the force of 1000 lbs pull on the rode. But to bury it that far requires a 1000 lb force! Yes the strength comes when a strong wind forces the anchor to dive, and it dives as deep as needed to counter the wind force. If there is no wind to force it to bury, it has to be dug in using the engine, and no small sailboat has an engine powerful enough to bury even a 25 lb CQR so that the flukes are buried in hard sand.
My experience is that many people in an anchorage are not well attached to the bottom and in a blow they will drag if the angle of burying is too high for the design of the anchor, and you need to be well clear of them.

In Cabo one winter almost all the boats anchored outside were lost when a storm blew in. They were anchored with chain in a shallow bay, and the waves came in and jerked the chains taught and pulled anchors. The only boat that escaped made its way out the anchorage and offshore.
Even a nylon rode would not have helped much as the anchor rodes all got tangled up as boats sailed off dragging their anchors behind them.

Now, in a quiet anchorage people can do all sorts of stupid things and no one is hurt by bad anchoring. But if you are anchoring to avoid bad weather, then you had better stay clear of anyone who doesn't know how to anchor properly, and if you are like me you dinghy around the anchorage asking people what they are using and how long is the rode.

Hope this helps somebody. It came from many years anchoring around Mexico, Hawaii, Bermuda and the Caribbean Islands.

Cheers all.

[noelex 77]

Originally Posted by waeshael

If there is no chance the rode can be chafed because of bottom conditions, then use all nylon rode, otherwise six feet of chain or so.

The advantage of nylon rode is in its ability to stretch. The biggest drawback is its vulnerability to chafe. Six feet of chain does not eliminate this concern. The ideal solution is to use an all chain rode with a nylon snubber. The nylon snubber provides the stretch and the chain provides a backup if the snubber is broken.

[daletournier]

[QUOTE=waeshael;2684490]

Originally Posted by thinwater

You will be wrong about this. On forums the deck is heavily stacked in favor of all-chain, but I can think of a few respected authors that have sailed far and at least one anchor manufacturer (Spade) that favor rope (with some chain for the bottom).


As I said the vast majority of boats that are lost due to anchors dragging in bad weather are anchored on all chain rode, or mostly chain rode.

There is a big difference in experience between those of us who are cruising as a lifestyle for years at a time anchoring in all sorts of harbors, and someone who spends only a few weeks anchored out. Most people are the latter. Few people experience very high winds at anchor, and never have to test their anchoring system's capabilities. For ordinary day anchoring where winds are under 25 its, the boat lies to the weight of the anchor and drag of the chain on the bottom and the anchor never gets solidly attached to the bottom (especially if in hard sand.)
Van Dorn is an expert on anchoring, and I would follow his advice for the most part, modified only by limitations of the vessel itself such as open stern which could fill with water and depress the stern to waves, roller furling (which causes more drag fwd of the CLR, and more yawing.) I think the best advice is to anchor where there is a short fetch to windward, and in protected waters where the waves can't build to more than a few feet. And of course only anchor in hard sand if you expect a blow. I think that knowledge of anchoring systems, of bottom conditions, strength of materials provides confidence and a good sleep. After sleeping aboard at anchor for more than 3 years at a time, It was very important to me that I knew without any doubt that no matter what happened that night, the anchor was properly bedded in and the boat very comfortable at anchor. My wife always felt safer on the boat at anchor than on dry land!

Cheers

How do you explain all the boats that have all chain that don't drag?

I can assure you that most of the cruisers I know that live in the the hook full time use all chain, there must be a reason for this? Some cats are an exception to this but most still have 50-60m of chain then ride.

[Jim Cate]

As I said the vast majority of boats that are lost due to anchors dragging in bad weather are anchored on all chain rode, or mostly chain rode.

And just how have you identified and quantified this sweeping statement? Sounds like another made up statistic, generated to support a questionable position.

You fail to mention the boats that are lost when their nylon rodes are chafed or cut by underwater sharp things, or that got them wrapped around their own keels. We have seen a few of those events personally in our years of cruising... if you are as experienced as you claim, I bet you have too.

You poo-poo the idea of the catenary of a chain rode being of benefit. We've found that the energy absorbed in straightening out catenary is a very important factor in reducing anchor loads. When coupled with the absorption of a nylon snubber, it is quite effective in reducing loads on the anchor.

And in the real world, laying out 10:1 scope as you suggest is required is bloody awkward in many anchorages... and if all those other ill informed yotties anchored on chain are not careful, you will be wandering about the anchorage quite differently than they will, and tangles and collisions may easily result. Not often appreciated, that practice!

But I guess I should thank you for setting us straight... those of us who live on the hook for days, weeks, years, and in our case, decades. We must just be lucky, since we've been doing it all wrong all that time.

Jim

Oh... did you ever see a ship anchored on nylon? Think how much more cargo they could carry if they didn't have those tonnes of chain up forr'ad.

[Bean Counter]

Originally Posted by captprogreso

If you are spending the night in a place 70 miles from any help with a good holding bottom at 10 feet but all around you there is a coral reef, would you trow a second anchor?
If yes, i allways deploy the second one with my tender, and if i try to retrive it with my sailboat, i allways get tangle so i need to retreve with the tender too, do you do the same ? In this place the wind is at least 15 knots, all night long.

Back to the OP, if the holding is good as you say, in sand I imagine surrounded by coral reef, then if it was me, I would anchor nearer the side with wind/wave protection, let out 7:1 scope (all chain) using a modern anchor such as Rocna, Spade, Mantus etc. I would allow a swing radius of 90 ft on my anchor alarm (to allow for GPS error and not getting exact co-ordinates of where anchor is set) and make sure that circle did not intersect with shallow water or another boat or structure (use the radar if you have one). If anchorage is too tight you could probably go to 5:1 in only 15knots of breeze.


If there is a strong tidal current which might over ride the wind then you might want to do a Bahmamian moor where a second anchor is set behind the boat but connected to the bow, this limits swing room and also the anchor is preset for the current reversal. We have never had to do this as we don't usually anchor in such places that need this arrangement, depends on how much room you have. The one time we did anchor in a swift tidal run surrounded by rocks (Double Breasted Cay, Bahamas) we set a stern anchor, a Fortress, it dug into soft sand so far it took ages to retrieve and a lot of mucking around.

[thinwater]

Just a few things.


Ships can use all chain because they are not affected by gusts and waves in the same way as yachts. They simply don't "feel" waves of the size you find in a river or harbor situation, and gust don't start the boat moving much. For a major storm, they will head outside. Thus, this is a false comparison.


Catenary is not an all or nothing thing. Over about 40 feet deep, you keep a lot of curve up to 50 knots. In 5 feet, it pretty straight at about 15 knots. Even then there is often a little curve, and most "all-chain" sailors do have some manner of snubber, which absorbs a little.



Additionally, like the ship example, as the water gets deeper and folks have 300 feet of chain out, there are other damping effects; it takes time of the wind or wave to move the boat to where the chain would snap tight, and by that time, the wave has passed; there is decoupling.


---


I'm with Nolex; a middle road with some nylon gives you the best of both worlds.

[waeshael]

[QUOTE=daletournier;2684553]

Originally Posted by waeshael

How do you explain all the boats that have all chain that don't drag?

I can assure you that most of the cruisers I know that live in the the hook full time use all chain, there must be a reason for this? Some cats are an exception to this but most still have 50-60m of chain then ride.

Answer:
In good weather when rode tension is only a hundred pound or less, any anchoring system will work, and that's what most people are exposed to. But in a storm even in a protected area like the pond in St Martin, an all chain rode will snatch at the anchor and pull it out. In shallow water there just isn't enough weight with the chain to provide the elasticity to deal with the pull and the chop. The nomographs for this are in Van Dorn's book Oceanography and Seamanship.

If as you say, everyone is using chain all the time, then all the boats that ever dragged had to have been using chain! And in Grenada in 2004, most of the anchored boats dragged in the hurricane and ended up ashore. Same in St. Martin.

My personal experience and that of my good friends who follow my advice, has been that the elastic anchoring system in which 1/2 inch nylon rode provides the elasticity, has kept their boats safe in bad conditions. I have anchored for more than 1000 nights on a nylon rode and it is still good. I never had any chafe on the bridal attached to the boat itself, and it is good after some 3 years on the hook. The rode is attached to the bridal ten feet away from the boat itself so it never is chafed. I would never anchor on a bottom that wasn't clean hard sand. I stay away from coral, of course, and rocky bottoms. If you have to anchor on those bottoms, though not me, a short length of chain would be good from the shank to the nylon rode.

Here is a PDF on what I do. Click on STERN ANCHORING link in the text
http://waeshael.com/waeshael.com/Anchor.html

Before you poo poo this idea asa well, I realize that Stern anchoring is not possible on many yachts because the stern is open or flat and exposed to the chop. But stern anchoring suits the boats natural tendency to put its bow downwind so it lies quietly to anchor even in gusting and changing winds. Loads on the rode are 30% less with stern anchoring, because the sides of the hull are not exposed to the wind, only the stern, so the boat can withstand higher wind speeds safely. This is all in Van Dorn's oceanography and seamanship book. I started doing the stern anchoring in 2000 in the Caribbean and ever since. For hurricane mooring at home I always stern anchor on sandy deposits in estuaries. And we get lots of hurricane scares in South Carolina.
We have weathered every near hurricane and storm with no damage to the gear. So from experience I am convinced that Van Dorn is right. he is a Naval Architect who also specializes in small boat anchoring.

But every man can do whatever he wants with his own boat. And most people have good experience with many different anchoring systems. But it can be a worry if you aren't absolutely;utely certain that the system you lay down will hold the boat in every weather condition whether you are aboard or not, and you have to know this from engineering principles, not from hearsay, otherwise you will worry. And I can see from this thread that some people, perhaps most people are not absolutely certain they are always doing the right thing regarding anchoring.

As far as myself: there is no longer any discussion on what makes the best and safest anchoring system. WhatI have is perfect.
I am just trying to educate others on what is best to do for a boat like mine anchoring in a good bottom of hard sand. Anchoring in mud is an entirely difference science, and anchors have to be selected for that type of bottom which depends on stiction to the mud. Sand is a plastic solid and behaves entirely differently.

Sailors ought to know the engineering principles of anchoring and not depend on sales brochures to make the decision on what is best for their boat. There is plenty of scientific data from the manufactures of commercial anchoring system, and from books like Van Dorn's who designs systems for large steel ships, Coast guard, and small traditional sailboats. Cats are a whole other situation, and I have no advice for them.

cheers

[noelex 77]

[QUOTE=waeshael;2684824]

Originally Posted by daletournier

I have anchored for more than 1000 nights on a nylon rode and it is still good.

With a bit more experience you will change your mind .

[waeshael]

[QUOTE=noelex 77;2684844]

Originally Posted by waeshael

With a bit more experience you will change your mind .

Iy has been a pleasure to contribute to this net as there are so many questions that I have the answer to from many years of engineering and sailing experience.
Now as to your comment:
Perhaps you would enlighten me was to your experience with anchoring? Can you point me to any engineering papers you or others have written on the subject? Have you experienced a hurricane at anchor? What type of ground tackle are you using for storm conditions?

I think we have entirely different boats, mine is quite light and easily handled alone, and my experience applies to similar sailboats as I have made clear in the posts. It doesn't suit all boats, nor anchoring in soft sand or mud.

I'm not sure whether your comment indicates that you think I am inexperienced with anchoring or you are being sarcastic. I have been cruising since 1970 in many parts of the world, in several sailboats, and have spent some six years at sea. I am an engineer, and now 75 years old. so be kind to an old man, and at least agree I have experience.
I have lots of experience lying to a chain rode, and it was years before I understood how to anchor a small boat safely.

Hopefully, others will be encouraged to investigate how anchoring systems work, and will not be discouraged through disparagement of nay sayers.

Thank you for at least reading the article. How about some advice from your end on how to anchor a larger yacht? Or perhaps you have already written about this? You may be some famous engineer and sailor, and I am just out of touch with the sailing community.

P.S,

I don't often comment on NETS like this, because most nets are encouraged to support the opinions of the majority. Hopefully this is not the case here. If responses to my posts were a put down, then I would see no point in continuing in contributing. Otherwise I look forward to future posts on subjects that I am an an expert on.

[Mike OReilly]

Originally Posted by Jim Cate

…You poo-poo the idea of the catenary of a chain rode being of benefit. We've found that the energy absorbed in straightening out catenary is a very important factor in reducing anchor loads. When coupled with the absorption of a nylon snubber, it is quite effective in reducing loads on the anchor. ...

Although my experience pales in comparison to the Cate’s, this too is what I’ve found.

I can see there is a benefit to all-rope with a smallish run of chain rode (my previous boat had this setup). The shock absorption is built into the system. But the catenary effect, along with decent snubbers, produce the same benefit. PLUS, all-chain comes with some clear benefits as has been outlined already.

The other thing I notice is that even in significant blows (50+ knots), my rode is rarely bone-hard for long. The catenary and the well-sized snubbers create a bounce-forward motion. The boat might then slide forward, and then fall back against one snubber (I always run dual snubber in a bridle). Seems to me with all-rope this larger bounce could more produce a higher shock load than the more gentle catenary/snubber thereby producing the exact effect waeshael claims is a problem.

Perhaps in a small, light boat the calculus swings to all-rope rode as being the best option. But on my 15 ton, full keel, I would not choose all-rope as my main rode. Not saying it couldn’t work, but I don’t think it would be as effective (having lived with rope rode in a previous boat).

… And yes, we anchor out most of the time, and have been for over a decade. I write this from a Newfoundland anchorage where we just managed a four-day gale, with winds hitting 40s. Never budged.

[noelex 77]

Waeshael, sorry if you took offence. My apologies.

However, there are many forum members that have more anchoring experience that have reached different conclusions to your suggestions.

The forum is about the exchange of ideas. No one has all the answers, but the concept of using mostly rope rode, even in coral waters, and anchoring via the stern in strong wind are practices that are not normally recommended.

[daletournier]

[QUOTE=waeshael;2684824]

Originally Posted by daletournier

Answer:
In good weather when rode tension is only a hundred pound or less, any anchoring system will work, and that's what most people are exposed to. But in a storm even in a protected area like the pond in St Martin, an all chain rode will snatch at the anchor and pull it out. In shallow water there just isn't enough weight with the chain to provide the elasticity to deal with the pull and the chop. The nomographs for this are in Van Dorn's book Oceanography and Seamanship.

If as you say, everyone is using chain all the time, then all the boats that ever dragged had to have been using chain! And in Grenada in 2004, most of the anchored boats dragged in the hurricane and ended up ashore. Same in St. Martin.

My personal experience and that of my good friends who follow my advice, has been that the elastic anchoring system in which 1/2 inch nylon rode provides the elasticity, has kept their boats safe in bad conditions. I have anchored for more than 1000 nights on a nylon rode and it is still good. I never had any chafe on the bridal attached to the boat itself, and it is good after some 3 years on the hook. The rode is attached to the bridal ten feet away from the boat itself so it never is chafed. I would never anchor on a bottom that wasn't clean hard sand. I stay away from coral, of course, and rocky bottoms. If you have to anchor on those bottoms, though not me, a short length of chain would be good from the shank to the nylon rode.

Here is a PDF on what I do. Click on STERN ANCHORING link in the text
http://waeshael.com/waeshael.com/Anchor.html

Before you poo poo this idea asa well, I realize that Stern anchoring is not possible on many yachts because the stern is open or flat and exposed to the chop. But stern anchoring suits the boats natural tendency to put its bow downwind so it lies quietly to anchor even in gusting and changing winds. Loads on the rode are 30% less with stern anchoring, because the sides of the hull are not exposed to the wind, only the stern, so the boat can withstand higher wind speeds safely. This is all in Van Dorn's oceanography and seamanship book. I started doing the stern anchoring in 2000 in the Caribbean and ever since. For hurricane mooring at home I always stern anchor on sandy deposits in estuaries. And we get lots of hurricane scares in South Carolina.
We have weathered every near hurricane and storm with no damage to the gear. So from experience I am convinced that Van Dorn is right. he is a Naval Architect who also specializes in small boat anchoring.

But every man can do whatever he wants with his own boat. And most people have good experience with many different anchoring systems. But it can be a worry if you aren't absolutely;utely certain that the system you lay down will hold the boat in every weather condition whether you are aboard or not, and you have to know this from engineering principles, not from hearsay, otherwise you will worry. And I can see from this thread that some people, perhaps most people are not absolutely certain they are always doing the right thing regarding anchoring.

As far as myself: there is no longer any discussion on what makes the best and safest anchoring system. WhatI have is perfect.
I am just trying to educate others on what is best to do for a boat like mine anchoring in a good bottom of hard sand. Anchoring in mud is an entirely difference science, and anchors have to be selected for that type of bottom which depends on stiction to the mud. Sand is a plastic solid and behaves entirely differently.

Sailors ought to know the engineering principles of anchoring and not depend on sales brochures to make the decision on what is best for their boat. There is plenty of scientific data from the manufactures of commercial anchoring system, and from books like Van Dorn's who designs systems for large steel ships, Coast guard, and small traditional sailboats. Cats are a whole other situation, and I have no advice for them.

cheers

Hmmmm...... You never anchor near coral or rocks or anything sharp, only hard sand?

No offence but you must have limited cruising experience.

I must of lived on the hook 3-4000 nights and I can assure you I haven't had the luxury of anchoring on hard sand all the time , it just doesn't work like that.

I understand what you are trying to say but unfortunately I disagree, in fact if cruising extensively I believe using rope rode to be dangerous. There's all sorts of things on the ocean floor.

[Cheechako]

No. Every time I have deployed a second anchor it has been a bitch to retrieve everything. Often with a big tangle. In your situation you want to be able to exit fast if things go wrong.
When you anchor, note a clear heading to exit out in the night.

[Cheechako]

Originally Posted by Jim Cate

And just how have you identified and quantified this sweeping statement? Sounds like another made up statistic, generated to support a questionable position.

You fail to mention the boats that are lost when their nylon rodes are chafed or cut by underwater sharp things, or that got them wrapped around their own keels. We have seen a few of those events personally in our years of cruising... if you are as experienced as you claim, I bet you have too.

You poo-poo the idea of the catenary of a chain rode being of benefit. We've found that the energy absorbed in straightening out catenary is a very important factor in reducing anchor loads. When coupled with the absorption of a nylon snubber, it is quite effective in reducing loads on the anchor.

And in the real world, laying out 10:1 scope as you suggest is required is bloody awkward in many anchorages... and if all those other ill informed yotties anchored on chain are not careful, you will be wandering about the anchorage quite differently than they will, and tangles and collisions may easily result. Not often appreciated, that practice!

But I guess I should thank you for setting us straight... those of us who live on the hook for days, weeks, years, and in our case, decades. We must just be lucky, since we've been doing it all wrong all that time.

Jim

Oh... did you ever see a ship anchored on nylon? Think how much more cargo they could carry if they didn't have those tonnes of chain up forr'ad.

Yep. In the Tobago Keys we were anchored in a two day big blow. The one day the anemometer was reading a steady 34 knots of wind, with gusts near 40. Fortunately the water was flat as we were protected, but a lot of load on the all chain rode. SO I decided to snorkel the anchor (Delta 44 on a 42 cat). The white sand bottom was easy to see that the Delta had buried itself completely ... no sign of the shank at all. The all chain rode still had probably 10-12" minimum of catenary in those winds. It's the WATER that jerks the rode tight if you are exposed.