Anchoring with two anchors

[M. R. Bober]

I have anchored with two anchors set Bahamian style (two rodes with a wide "V" in their set) twice. In both cases I had one anchor set when conditions worsened. In one case, I had a snapped shaft and had no other option to protect the boat and the crew (I was single handing).

Given my choice, I would have preferred to have set the two anchors in tandem on a single sturdy rode with a length of chain between the anchors. The idea of a kellet has great merit--IMHO--in that it can be retrieved independently, with less muscle power than hoisting a heavier rode/anchor combination.

Like so many other seamanship issues, anchoring is a matter of personal experience and opinion. In the end, you must know the capabilities of your equipment and crew.

John: I would not trust that rubber dock line snubber with my rode.

Mitchell Bober
Sunny Lancaster, (where Mother Nature sides with the hidden flaw) VA

[Maine Sail]

Snubbers, stretchy ones, are a necessity with all chain. If you think the weight of a chain or kellet will keep your caternary in storm conditions think again. The shock loading from all chain can be very harsh on equipment.

This is very, very heavy mooring chain in under 40 knots snapped near bar tight.

[/img]

[Jim Davis]

John

I don't think I would use that shock absorber on a snubber. While it would reduce shock load, it might cause the hook to drop off the chain when you surge back toward the anchor. If you were to "mouse" the hook on your snubber it would probably be OK. For me the answer is a long snubber, with a "moused" hook. If I expect storm conditions I will break out a mooring line and secure it to the chain with a rolling hitch.

For those who do not like chain I want to point out that chain chafes rock and coral. Rock, coral and other obstruction chafe rope. Also I have had other boats cross close enough to my bow to have picked up a nylon rode if I had been using one.

As to the affect of storm winds/waves on the rode. When I'm anchored I try to use a seven to one scope (ten to one for heavy weather). I know I can lift a lot of chain when wind/waves push me back, however the load on the anchor stays a lot closer to horizontal than if I were using a short length of chain and an equivalent length of nylon. Again a snubber is vital to reduce shock loading.

To compare what chain does by referencing how it works on a mooring isn't really a valid comparison. Most moorings only use a scope of two (or three) to one, with a 300+ mushroom. This is not comparable to what is considered prudent for normal anchoring with standard anchors.

[Klem]

To the OP's question, using 2 anchors is simply not very effective for several reasons. Primarily, the issue is that you can never do a very good job of balancing the load between the two anchors so one will still tend to take most of the strain and drag. This will self equalize somewhat but the dynamics of the situation mean that it never equalizes for very long. Making the situation worse is that there are often wind shifts involved in major weather events. During a wind shift, it is likely that the anchor taking the strain will drag into the other anchor and they will foul each other. Using significantly different length rodes can lessen the chances of this but it is still a distinct possibility. Retrieval can be a pain but a short piece of line and a rolling hitch carefully placed usually allows everything to be untangled. On larger vessels with very large chain, it can be an absolute nightmare (I have spent half a day working on one).

The biggest benefit to 2 anchors in my opinion is that the boat will be less likely to "sail" around on the anchor. Cape Dory's tend to sit fairly well to an anchor but they do start to move around a lot in really high winds. If you are ever dragging your primary anchor, put at another by all means but it should only be as an emergency measure instead of something routine.

The OP mentioned that he is hesitant to go bigger than a 22lb bruce for various reasons. Have you tried looking at other anchors in the same size range such as a Rocna, Manson Supreme or Spade? The Bruce anchor was great in its day but there are anchors that set faster, stay set better and have higher holding power for the same weight these days. Personally, I would not feel comfortable with the ground tackle that you have in any form of severe weather. Many tests have found the holding power of those anchors to be on the order of several hundred pounds while the published expected 60 knot load on the boat is well over 2000lbs (these tend to be a bit high). For comparison, I use a 33lb Rocna on my 30k and I have had 50+ steady over the deck with this arrangement.

To the other debate in here about catenary and snubbers, good scope and a good snubber are by far the best solution. Catenary in chain is almost non existent in severe conditions where you need it the most. Anyone who has ever seen 40+ over the deck will tell you that the chain is absolutely straight. The picture posted by Maine Sail is a great representation of this. The conditions in the picture are not that rough, yet there is no catenary to either lower the angle of pull or provide shock absorption. If you have never played around with a catenary calculator (just google it), the expected storm windload for you boat and the chain you use, you should. It is truly eye opening how little deflection there will be in the chain and how little elongation has so much effect on the force applied. This is really the subject for another thread but as mentioned above, put the weight in the anchor itself and give it a lot of scope and a good snubber.

[Maine Sail]

To compare what chain does by referencing how it works on a mooring isn't really a valid comparison. Most moorings only use a scope of two (or three) to one, with a 300+ mushroom. This is not comparable to what is considered prudent for normal anchoring with standard anchors.

No your right it's not valid mooring chain usually weighs more than 1/4" or 5/16" anchor chain..

75' of mooring chain: = 790 pounds (45' USCG @14 Lbs ft X 25' 3/4" top chain @ 5.3 lbs. ft)

250' 3/8" chain = 392 pounds
250' 5/16" chain = 250 pounds
250' 1/4" chain = 182.5 pounds

250' is 7:1 35' of water my mooring is in 30' at high tide for a 2:5.




50 Knots, 40' boat, 33 pound kellet, 100' of 3.8" chain near bar tight. Having a good anchor in this scenario is the only thing that will help.

Images Courtesy Peter Smith:


50-60 knots no effective caternary remaining in this all chain rode.


Keep in mind that a 10:1 scope really does not help much other than to increase your swing circle. At an 8:1 scope the max angle of pull on the anchor will be approx 7° even with bar tight rode. In order to half this number you'd need to double your scope. Going beyond 7:1 or 8:1 does not gain much and the gains require lots more scope. Of course it can't hurt either if you have all the room in the world.

I have no problem with all chain, heck I have 250' of 3/8" in my anchor locker, but I'd take 8:1 nylon/chain over 5:1 all chain every day of the week in a storm. In fact I use all chain in tight anchorages and nylon/chain 60' chain/300' nylon in storms. I would much rather put my money into a better or bigger anchor than chain and I like the shock loading protection that nylon gives that I just don't get in a 20'-30' snubber. In real storms caternary quickly dissipates and the anchor & scope becomes what you rely on..

This is what ONE good anchor will do..
http://www.youtube.com/watch?v=luWJwTRkTUo[/url]

[WaywardWind]

Keep in mind that NO one chains a boat to a dock, or a rock on shore.

Why?

Because it breaks things, even in small wave conditions.

People who chain their boat to an underwater rock also break things. Unless they get lucky. And the odds almost always catch up with those who feel they are somehow luckier than the average guy.

Best use of an all-chain rode is running through the electric windlass easier in lite air conditions.

Effective snubbers need AT least 5 feet of stretch, with more being far, far better. 30 to 50 feet or more of three-strand nylon or plait is prudent seamanship in storm conditions. Anything less is negligence.

~~~"Also I have had other boats cross close enough to my bow to have picked up a nylon rode if I had been using one. "~~~

Hang a 10# mushroom anchor on your stretchy nylon rode out about 15 feet from the bow. That will pull the nylon under the water so no other boats can catch it. Use a nylon line to the mushroom with a large loop in it, wrap the line around your rode twice and thread the bitter end through the loop for an instant Prusik knot, then clip the bitter end to the mushroom. Instant kellet.

[SurryMark]

Having dealt with twisted lines, I'm for the single anchor with all the parts in good order, and good chafing gear. (Though I did have a second anchor plus my mushroom during a hurricane, and the second anchor line served to catch and hold a drifting boat until the storm blew out.) My question is about the large anchor everyone talks about. My 10kg Rocna (40' 5/16 chain + 200' 3/4" Brait w/snub) has worked fine in all conditions so far, though never more than about 30+ kts. The 10kg Rocna is listed as OK for a 30' 5 ton boat, which means mine would be over-sized. Is that what people talk about when people mean "heavy," or do they mean woppingly over-big? And then there's the issue of what you want to pull up day-in and day-out.

[M. R. Bober]

Having dealt with twisted lines, I'm for the single anchor with all the parts in good order, and good chafing gear. (Though I did have a second anchor plus my mushroom during a hurricane, and the second anchor line served to catch and hold a drifting boat until the storm blew out.) My question is about the large anchor everyone talks about. My 10kg Rocna (40' 5/16 chain + 200' 3/4" Brait w/snub) has worked fine in all conditions so far, though never more than about 30+ kts. The 10kg Rocna is listed as OK for a 30' 5 ton boat, which means mine would be over-sized. Is that what people talk about when people mean "heavy," or do they mean woppingly over-big? And then there's the issue of what you want to pull up day-in and day-out.

Mark,
IMHO, you cannot have an anchor that is too big, unless you can't hoist it back on deck. When I had TIA MARI (1979 CD27) I used a Danforth 20H as my primary anchor. This anchor was/is rated for a 50 footer in up to 20 knots of wind. It always held, and I slept well.

I just bought a 20kg (44lb) Rocna for STARVIEW.

A good anchor is cheap insurance.

Mitchell Bober
Sunny Lancaster, (where the season is just getting started) VA

[Duncan]

Mitchell, your puns are twice as funny on this thread

Duncan Cameron
Frozen Montreal (where all the boats have been dragged ashore for the winter), QC

[wstringer]

Mitchell,

How does the 44 lb Rocna fit on a CD 36 bowsprit? Is there room for a bigger one? I have been looking at replacing my 35 lb CQR and 44 lb Bruce with a single big anchor, maybe a 55 lb or even the 73 lb Rocna.

Thanks,

Warren Stringer
s/v Eendracht
CD 36 #54, 1981

[Klem]

Having dealt with twisted lines, I'm for the single anchor with all the parts in good order, and good chafing gear. (Though I did have a second anchor plus my mushroom during a hurricane, and the second anchor line served to catch and hold a drifting boat until the storm blew out.) My question is about the large anchor everyone talks about. My 10kg Rocna (40' 5/16 chain + 200' 3/4" Brait w/snub) has worked fine in all conditions so far, though never more than about 30+ kts. The 10kg Rocna is listed as OK for a 30' 5 ton boat, which means mine would be over-sized. Is that what people talk about when people mean "heavy," or do they mean woppingly over-big? And then there's the issue of what you want to pull up day-in and day-out.

Everyone seems to have their own definition of over-size so here is my take on it. A lot of people seem to simply base their definition on weight or looks but I base it on expected holding power.

As an engineer, I approach the problem by saying what does the anchor need to do? In my opinion, anyone that gets more than an hour or so away from their mooring/berth and is in places where squalls are a possibility needs to at least have ground tackle capable of working in squall conditions with the expected bottom conditions. Whether you then opt for an anchor that has better holding than that is a question as to whether you expect to ever face conditions worse than that. This depends on your hurricane plan. Turning the expected conditions into a required holding power isn't an exact science but the formula used by the ABYC is a good conservative start. This is where I personally apply my "over-size" factor. Sizing for 20 knots more than expected gets you a pretty large anchor. There are also other, just as important consideration such as setting ability and veering behavior but they don't have an effect on the anchors size really.

To correlate this required holding power to an anchor size is tricky again. By carefully looking through the data from anchor tests and the bottoms that they were done on, some idea of holding power can be gathered. Additionally, some manufacturers publish helpful data in terms of holding power. Fortress is probably the most helpful here although their anchors do not meet some of my other requirements for a primary anchor. Rocna is reasonably helpful in what size anchor they recommend by using 50 knots and average holding bottom. Ideally, I would want to see a mean and standard deviation of holding for every possible bottom type. You shouldn't be sizing with the mean because approximately 50% of the time, you will have less holding power. You should really be sizing so that 95% or so of the time your holding power exceeds your requirements. I have yet to see this data though so I use a bit of a fudge factor.

This exercise yields wildly different size anchors depending on the model for the same boat. For example, a fortress might need to be 1/4 the weight of a cqr. Pertaining to your boat with the Rocna, I would say that it meets the squall requirement that I laid out for most bottom types (and meets all of the other anchor requirements I didn't go through here). If it were part of a hurricane plan, I would get a 15kg at least and it would certainly be "over-size". Compared to the vast majority of people out there, I think that your anchor is already over-sized based on holding power.

This is a relatively conservative way to pick an anchor size and is based on the worst case scenario but you can't redesign your ground tackle when you suddenly see a severe thunderstorm heading your way, it is too late. There is nothing worse than sitting in a hurricane hole watching another boat come and anchor near you with undersized ground tackle. I have had the owner of a 50' trawler tell me that his 45 lb cqr was "massive" while anchoring for a tropical storm. Needless to say, I moved and he was up on the beach the next morning.

I hope that this helps. It is only one definition.

[M. R. Bober]

Mitchell,

How does the 44 lb Rocna fit on a CD 36 bowsprit? Is there room for a bigger one? I have been looking at replacing my 35 lb CQR and 44 lb Bruce with a single big anchor, maybe a 55 lb or even the 73 lb Rocna.

Thanks,

Warren Stringer
s/v Eendracht
CD 36 #54, 1981

Warren,

I will let you know.

My original intent was replacing the CQR #35--on the boat at time of purchase--with a CQR #45. The CQR #45 does not fit "through" the uprights on the Spartan R610S (anchor roller) so I investigated the options and liked the reports on the Rocna.

Rocna has an online template that you can download: http://www.rocna.com/product-range/boat-fit/. I did and it seemed to fit, but I have just received the anchor and it looks very close.

I will be taking the winter cover off very soon and then I will see just how close the fit is.

Mitchell Bober
Sunny Lancaster, (where nothing ever goes wrong) VA

[mike ritenour]

Over the years of voyaging LaVida, in all sorts of anchoring conditions, through the Great Lakes, Canadian Maritimes, East Coast, Bahamas and Northern Caribbean, we've evolved several techniques and equipment configurations that have worked for us.

LaVida's ground tackle equipment: we carry a 35# CQR, 22# Delta and a 75# Luke breakdown (our last stand anchor), 150' of s.s. chain, a backup 250' of 5/8" nylon, a 10# kettle and my own designed snubber and an anchor float tied to a small kevlar line for pulling the anchor out backwards, if necessary.

The snubber consists of 8' of 5/8" three strand nylon woven through the snubber and terminating in a spliced eye with a chain hook at the end.

Another critical piece of gear in our anchoring system is our riding sail. The riding sail stabilizes our swing, helping to limit the sailing at anchor caused by our cut away forefoot.

Usually I lay out a 5 to 1 scope, out of habit, no matter the holding ground, using full chain and my snubber (with the snubber in place, the surge loads shocks are eliminated) which creats a bight of about 4' of chain hanging down loose and not under tension.

The four foot is about the max the snubber and nylon will stretch. At that point of max stretch, the full weight of the chain comes on line and takes up the full anchor load.

In severe storm conditions I will shackle my Delta onto a 10' chain pigtail to the eye of my CQR putting them into "tandem". With both anchors laid out in tandem, I find it limits plowing, even through soft bottoms. In addition to the tandem setup I will, in severe conditions, add the kettle downstream of the snubber connection into the mix.

Diving on this setup after a Northern front hit us in Chub Cay, Bahamas (winds gusting to 50kts, many times with solid water coming over the bow, for over 40 hours) I found the Delta buried in about 3' of sand, the chain pigtail completely buried and the CQR just barely visible. We didn't move an inch, while three other boats around us, on full chain, were driven onto a nearby reef.

It was a hell of a job getting it all out, as we were so firmly set, but I did not have the complications of twisted anchor lines and only the roar of the wind kept us awake, not the fear of dragging.

Over the years, if I have any doubt of my holding ground while I sleep, the full chain, snubber system and tandem anchor spread provide some peace of mind.

[Dick Barthel]

This has been a very good thread which seems to put to rest my thoughts of deploying two anchors. I haven't had time to study every response but I take from what I have read that if I had my boat anchored in an area effected by significant tides where you can normally expect a 180 swing on the ebb and flood and if you might be anchored for a week at a time that you would definitely not use two anchors in an offsetting V arrangement and if you had concerns you'd go bigger.

I have a 25 lb CQR that has never failed me in this situation which has sandbar for bottom. I assume when the boat turns the anchor resets. Maybe Cathy's suggestion would provide some further protection for the chance that the CQR doesn't reset on the swing for some reason.

The V arrangement still seems to make some sense if you're expecting a real blow of short duration and you will be on the boat and keeping an eye on things.

That GPS image of the movement at anchor is mind blowing.

Dick

[Evergreen]

Warren:

A couple of years ago we traded out a CQR 35 and a similar size Bruce for a Rocna 55 as our bow anchor, with all chain rode, on our CD 36. It is one of the best moves that we have ever made! We also use a Best Marine anchor chain claw with double snubber lines (expensive but well worth it). We have never dragged in a wide variety of bottoms and conditions! The anchor fits well on the bow roller, although the chain needs to be kept tight so that the anchor does not wobble side to side. After one year of back breaking anchor hauling we also added an Ideal horizontal windlass.

I knew we were getting close to the appropriate anchor size when I started to see eyebrows go up when people walked the docks looking at boats. We have become strong believers in Rocna anchors and also the fact that size does matter. Now we look a boats with smaller anchors and just shake our heads and wonder how people could possibly believe those tiny little lightweight anchors could hold such large vessels.

Regarding second anchors --- we have found that the rodes nearly always end up twisted! Consequently we took our second anchor off the bow. If we ever do use a second anchor ---we use a fairly light Delta 22 with fifty foot of chain and the rest nylon rode for the sole purpose of limiting the boat from sailing on her anchor (which causes significant loading on the primary anchor in storm conditions). We dinghy it out at a 90 degree angle and then snug it up so the boat does not swing. If the two rodes get twisted it is no big deal since the bitter end of the smaller anchor is not permanently attached. We just pass the end around the chain to get the two untangled.

Aside from using too small an anchor the other biggest problem that we frequently observe is that folks chronically use too little scope. If there isn't enough room to put out scope then you should move to another spot.

In summary, our opinion is to go Rocna and GO BIGGER (a 55 is NOT too big for a CD36). You will sleep much better.

Hope you find this useful.

Best wishes,