Anchor Size: Multihull v. Monohull

[44'cruisingcat]

Originally Posted by Xlantic

True but in oil rig use, setting and resetting is not as important as it is for a cruiser.

The Bruce has a very high holding power (twice as much for a given weight as a Danforth according to oil-rig anchor manufacturer Vryhof) but from the tests I have read about and my own experience it is not very good or quick at setting and resetting.

Funny, but that's the exact opposite of my experience.

[44'cruisingcat]

To the OP, in general it seems you use an anchor about the same size as you would for a similar length mono. ie. One size up from what the anchor manufacturers recommend.


Your boat is much lighter, but has more windage.

[tomfl]

Just my two cents.

Threads about anchors (and guns and global warming) often get way out in the woods very quickly. A search on the topic will usually reveal agreement on a few things.

First off you will often see the term ground tackle which includes the anchor, the combination of chain and rode used to connect the anchor the boat and the idea of a bridle and how it can change some things. Another concept is that different anchors work better or worse on different types of bottoms, leading to the idea that a boat should have two different types of anchors.

In general lots of chain will make any anchor perform better. Good anchoring technique like looking for a good place to anchor, letting chain out in stages, waiting to see if the anchor is set, and then backing down on the anchor greatly reduces the chance of dragging. Most multihulls use a bridle when anchoring. A well designed and deployed bridle can reduce the effective freeboard so you may be adding a couple of feet or less instead of the five feet many monohulls need to add. A well designed bridle can also greatly reduce sailing at anchor. Tris in particular often have a bridle attached to the amas which often have as little as a foot of freeboard. Another factor is many bridles have snubbers which reduce the force of jerks from bobbing on waves.

The point is a well thought out ground tackle system is a whole lot more than the choice of anchor. It is easy to make a good anchor look bad and a bad anchor look good depending on the skill used in setting the anchor and the choice of ground tackle.

That being said I have a 15kg Manson with 150 feet of chain and 150 feet of 3/4in nylon and a bridle with snubbers on both links of the bridle and a 35 pound Bruce with 50 feet of chain and 200 feet of nylon on the bow of my Seawind 1000. It works for me.

[Sailing55]

Originally Posted by Xlantic

True but in oil rig use, setting and resetting is not as important as it is for a cruiser.

The Bruce has a very high holding power (twice as much for a given weight as a Danforth according to oil-rig anchor manufacturer Vryhof) but from the tests I have read about and my own experience it is not very good or quick at setting and resetting.

I carry Bruce, CQR, Danforth [original seaplane anchor], and fisherman style...when I need to stay put in heavy conditions, it's the Bruce that goes down.
I never leave my boat if there is any chance of sailing around the anchor, and the Bruce lets me rest easy.

And your first sentence makes a good point, but there is something comforting about envisioning a North Sea Oil Rig being solidly held in position by my favorite anchor. :]

[thinwater]

What is Ideal Snubber Size? - Practical Sailor Print Edition Article

I did a lot of load cell testing with different snubbers and winds with a 34' cat. Also compared experiences with some reasonably well known cruisers/authors.

Displacement matters. Length matters, to the extent that it is related to windage. As for anchors, the bottom matters more than anything else; small anchors work in sand, but bad bottoms have few fixed rules.

[thinwater]

Originally Posted by Xlantic

True but in oil rig use, setting and resetting is not as important as it is for a cruiser.

The Bruce has a very high holding power (twice as much for a given weight as a Danforth according to oil-rig anchor manufacturer Vryhof) but from the tests I have read about and my own experience it is not very good or quick at setting and resetting.

Bruce rig anchors have nothing in common with Bruce recreational anchors. They do some good things, but have at least 10 less hold in sand and much than, say Fortress. Not to say I wouldn't use one for rock and gravel.

[donradcliffe]

Originally Posted by 44'cruisingcat

Funny, but that's the exact opposite of my experience.

ditto for me.

Once the danforth is set it has really high holding power, but will foul on tide/wind reversals. The Bruce has very little surface area and slides easily through soft bottoms. The Bruce has a lot of trouble setting in weedy bottoms like the Med--I would have to dive down andwork the anchor by hand as my wife backed down

[TrentePieds]

What we call a "Bruce" is indeed a miniature version of the anchor Peter Bruce designed for use by oil rigs in the North Sea way back in the 60's. I don't know what the gizmo in the pic is, but it ain't a "Bruce" :-)

I knew Bruce slightly through a hengeneer-type friend in Vancouver and had a conversation with him about why his device was so "exotic". Among the things he told me was that it was specifically designed for the sandy ground that you find in the North Sea, and that these anchors (at a coupla tons apiece) were laid out in bridles from each corner of the rigs then in use, each leg of the bridles having three anchors in tandem. Therefore there would be no question of the pull on the shanks changing direction. He also told me that "surface roughness" of the anchor casting in relation to the anchor's dimensions had an effect on it's holding power.

Other posters have made significant comments: 1) the hook itself is only one part of the "system". 2) Total weight of gear on the bottom (hook or no hook) is of the utmost importance and 3) anchors have to be selected for the specific combination of holding ground, wind and wave that obtains at the time of anchoring. I thot that was a very timely reminder. There really isn't such a thing as a universally "best" anchor. I think it's possible to select an anchor that works best for you in most of the places you "normally" go, in the conditions you "normally" go there. But universally "best"? Well, if you expect the impossible, you WILL be disappointed :-)!

TrentePieds came with a 35lb Bruce for a bower with 40 feet of 5/16" chain and 200 feet of 1/2" nylon and a 7 lb Fortress with 150 feet of 1/2" nylon, but no chain for, a "stern" anchor. I added a 250 foot "shot" of 1/2" nylon to deploy when, and if, needed. For what we do, that is adequate.

The notion that and anchor should be "lightweight" (a "selling point" for the Fortress) misses the whole point, in my opinion. If you are a kayaker, then okay. But for a yacht? No! What's needed is LOTSA weight on the bottom and as long a scope as circumstances and you gear will permit. And, if it blows, a scrupulous anchor watch!

TrentePieds

[tomfl]

Originally Posted by thinwater

What is Ideal Snubber Size? - Practical Sailor Print Edition Article

I did a lot of load cell testing with different snubbers and winds with a 34' cat. Also compared experiences with some reasonably well known cruisers/authors.

Displacement matters. Length matters, to the extent that it is related to windage. As for anchors, the bottom matters more than anything else; small anchors work in sand, but bad bottoms have few fixed rules.

I would point out there are multiple types of snubbers. I was talking about the rubber ones you basically wrap some line around. My bridle is composed of two length of line both attached to a single chain hook so if one side breaks there is still one side intact.

[RaymondR]

My experience with Bruce style anchors in comparison to plow and Danforth types is that the Bruce style set much faster and more reliably than the plough and about the same as the Danforth. However the stabilizers on the danforth often foul the anchor chain.


The Bruce style do not hold as well as either the plow or Danforth but they do reset much more reliably than the plow and Danforth and stow nicely on a bowsprit.


The commonest anchor used by oil rigs before the development of a number of improved designs for use in the North Sea was the LWDT or Light Weight Delta Type. These had insufficient fluke area to be a high holding power anchor and had the bad habit of burying themselves so deep into the clays which characterize many offshore sea beds that they often could not be retrieved. There was a rash of development in response including the Bruce and Flipper Delta.

[Lucky]

Originally Posted by Gone2long

Thanks, will check it out.

G2L

I have replaced the 45lbs CQR on our Belize 43 cat to a Rocna 33kg approx 77lbs and it is absolutely fantastic, sets directly and has not let us down. Before the switch I spoke to a person in the harbour that had a 20 kg Rocna on a 40' light cat and he claimed that my only problem would be to get the anchor out of the ground!

The Rocna also claim they are the ony one to set in seagrass. I have not tested this but the extreamly sharpe edges at the point should probably help in doing this.

As advised earlier in the tread a 20kg Rocna would do the trick. Also to help limit swinging it would be good if you could have a bridle from each of the ama's rather than the central hull.

Safe lead free sailing from Lucky

[Gone2long]

Originally Posted by kas_1611

As a convert from a Delta to the Rocna Vulcan I can vouch for the performance of the Vulcan. Sets extremely quickly, normally in less than an anchor length, and will hold you secure in normal conditions on 3:1 quite happily.

Other similar new generation anchors such as the Rollbar Rocna, Mantus, Manson Supreme are also good options to look at. For my boat at the size of anchor I was looking at the Rocna and Mantus would not fit on the roller but then I was looking at 30kg+ anchors. Compare that to the 16kg Delta I had originally! We plumped for the 33kg Vulcan based on the theory that the bow anchor should be a storm anchor capable of holding us in 60kts.

Hope that helps

Keiron

I do not mean that as a joke or an insult.

What I am wondering is, do you think that there would be any way to stay anchored I such a storm? I assume that the only safe thing one could do is to head for a mooring in a harbor where one could tie up to a sturdy pontoon. Unfortunately, that may be impossible where I will be sailing in the next few months, and such storms are known to frequent that region on occasion.

Your thoughts?

G2l

[Gone2long]

Originally Posted by roland stockham

You are right to think that ground tackle for a multi does not work the same as a mono. Basically a traditional mono with plenty of keel area should lay relatively stable pointing into wind and not yaw aroud. She should also be a very good load carrier. So not so much anchor stress and the ability to carry big anchors and chains (the chain being a vital part of the system). In my case my 'storm' anchor is 2 35lb bowers rigged in tandem with 100m 10mm chain that can be extended to 150m with a second rode. That's 700lb, how much difference is 10lb in the anchor going to make? I once tried winching a rode with 30m of 8mm chain and no anchor set across a mud/gravel bottom from a boat aground (trying to pull a boat into deep water when the tide did not make). Using 2 primary winches via a bridal for 2:1 purchase I could not get enough power to drag the chain, remember there was NO anchor on the end!
Most mult's (or lightweight monos) don't want to be carrying 1000lbs+ in ground tackle so use short chains, light anchors and rope roads. In my book it is what the new generation anchors are specifically designed for, high holding power in a light weight, basically go for the biggest one you can carry, think about using tandems and don't anchor up wind from me!!!

Yes, I understand. However, like one of the other posters above, I AM the windlass, and I am not a young man anymore. Pulling up even 50 or 60 feet of chain over a rocky/coral bottom is pretty taxing, so we really do need to go as light as is reasonable.

Thanks for your advice,

G2l

[Gone2long]

Originally Posted by 44'cruisingcat

To the OP, in general it seems you use an anchor about the same size as you would for a similar length mono. ie. One size up from what the anchor manufacturers recommend.


Your boat is much lighter, but has more windage.

Roger that. Thanks.

G2L

[Gone2long]

Originally Posted by tomfl

Just my two cents.

Threads about anchors (and guns and global warming) often get way out in the woods very quickly. A search on the topic will usually reveal agreement on a few things.

First off you will often see the term ground tackle which includes the anchor, the combination of chain and rode used to connect the anchor the boat and the idea of a bridle and how it can change some things. Another concept is that different anchors work better or worse on different types of bottoms, leading to the idea that a boat should have two different types of anchors.

In general lots of chain will make any anchor perform better. Good anchoring technique like looking for a good place to anchor, letting chain out in stages, waiting to see if the anchor is set, and then backing down on the anchor greatly reduces the chance of dragging. Most multihulls use a bridle when anchoring. A well designed and deployed bridle can reduce the effective freeboard so you may be adding a couple of feet or less instead of the five feet many monohulls need to add. A well designed bridle can also greatly reduce sailing at anchor. Tris in particular often have a bridle attached to the amas which often have as little as a foot of freeboard. Another factor is many bridles have snubbers which reduce the force of jerks from bobbing on waves.

The point is a well thought out ground tackle system is a whole lot more than the choice of anchor. It is easy to make a good anchor look bad and a bad anchor look good depending on the skill used in setting the anchor and the choice of ground tackle.

That being said I have a 15kg Manson with 150 feet of chain and 150 feet of 3/4in nylon and a bridle with snubbers on both links of the bridle and a 35 pound Bruce with 50 feet of chain and 200 feet of nylon on the bow of my Seawind 1000. It works for me.

Thanks a lot Tom,

I appreciate your holistic approach; it was very informative to a new skipper like me, and it makes a heck of a lot of sense. One's "chain" has to be solid. One weak link, and all the strength is for naught.


Will be doing more research on bridles, etc., so you may hear from me again in the future.

Best Regards,

G2L