Anchor Size: Multihull v. Monohull

[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

[Xlantic]

Originally Posted by Gone2long

I am wondering if these stats are accurate for a multihull. For instance, I have a light boat with negligible displacement; but, on the other hand, the boat is wide, creating a lot of windage on three different hulls. G2l

According to this site, a trimaran will have more windage than a monohull but less than a catamaran.
Forces

[hamburking]

Originally Posted by boatman61

Damn.. and there's me been using a Bruce successfully for 35yrs... but I guess 'Idiot Proof' anchors have their use's.
Just wish more Charter boats had them.. idiot proof anchors I mean

I'm also a fan of bruce anchors. I've been using nothing but for years.

One night, at my favorite anchorage in the islands here, it blew 40knots. Just about every boat dragged, including me (which is rare, cause I never drag). One little Grampian 26 did not drag, and I could see the skipper, confident, as I hauled up my rode in the night. The next day, I asked about his gear...and that was the first time I heard the word ROCNA.

[boatman61]

Originally Posted by hamburking

I'm also a fan of bruce anchors. I've been using nothing but for years.

One night, at my favorite anchorage in the islands here, it blew 40knots. Just about every boat dragged, including me (which is rare, cause I never drag). One little Grampian 26 did not drag, and I could see the skipper, confident, as I hauled up my rode in the night. The next day, I asked about his gear...and that was the first time I heard the word ROCNA.

Ahhhh.. but WHICH ROCNA...??

[barnakiel]

I would consider 35 pounds VERY light. We have a 35 pounds anchor in a 26 ft boat with only 2 ft of topside height and a most moderate displacement.

Unless your anchor is but a lunch hook, go for one that will let you sleep well no matter what.

b.

[Stu Jackson]

Why NEW GEN Anchors are Better:

Anchors & TEST Results of New Generation Anchors EXCELLENT & Important

Anchor System Sizing Tables (Reply #6) & Why Swivels are a bad idea Ground Tackle & Anchor System Sizing TABLES & Swivels

[Sailing55]

Originally Posted by AD28

I have a 40' 16.5K lb cat.

She lays to chain with a 45 lb Manson Supreme, and has done so through a 180 degree shift with a 50kt blow accompanying it; a 60kt blow emergency set; a 50kt squall; and a 30kt t-storm with fetch. (those are my worst so far that I recall)

I do not skimp on scope. To me, short scope is 5:1, and I'm normally setting on more (except that emergency set)

35lb is the low end but you're probably ok. Scope can make up for many of an anchor's flaws.

That said, don't touch a Bruce/claw with a 20' pole. In the 'emergency set' situation a boat which was (not) laying to a Bruce drifted down on me, the only one in the anchorage who came off his hook. Bruce. Not even once.

btw this is a very interesting series of videos of anchor setting that a talented amateur has produced. Read that to mean, 'not done by an interested party.'
https://www.youtube.com/user/flygoodwin

Are you saying that all the oil rigs that use the Bruce anchor are using the wrong anchors?
After all, what would the guys working oil rigs know about heavy seas?
All the same I will keep my 30kg Bruce [storm anchor] for my 10 ton boat, just in case...

[Tom and Maje]

We have a Rocna (I may have misspelled that) and love it. The only time we've dragged has been out fault.

[Gone2long]

Originally Posted by UNCIVILIZED

Yes, your initial post was penned in such a way so that you made it sound as if you were shopping for anchors. And that your primary candidates were 35lb Lewmar; Delta's, & CQR's. Or so I believed after reading it.

As to insights, I've a few:
- 35lb (or a bit more) is perhaps big enough for a Danforth for a boat that size. Your primary hook should be a good bit bigger.

- Scope: You need to use more of it. A LOT more. Because... If you're in 13' of water, & your bow's 5' high, plus, most places, there's a minimum of a 5' range of tide. Then your ground tackle is operating with 23' of "depth" to deal with. So that if you have 50' of rode out, you're on 2:1 scope.
Which is where Tarzan would say: "That's Bad Juju Bwana". Especially if/when, on top of that; the breeze goes up, the boat swings (due to wind or current/tide), or, some seas build... which leads to the next item.

- 20kts ain't much more wind than comes out of someone's backside, after eating a bowl of chili.
As a realistic minimum, you're ground tackle should be up for twice that (which means 4x more load, from wind only). Or better yet, 3x that, aka 9x load. If you're wanting ground tackle for a serious cruising context, that is.

Plus, when it's blowing like that, most any boat's going to be yawing, & or, sailing back & forth a fair bit (some even maniacally). Thus increasing it's windage (& subsequent ground tackle/anchor loading) by that much more.

- And then, there's the "serious bits". Waves & fetch. As the shockloads from them can be pretty unfriendly on your entire ground tackle system. Especially with regards to your anchor's staying in the same zipcode.
Particularly when the weather comes in from an unexpected direction, & you're now on the wrong end of a mile or more of open water, over which the waves can build.
Ever seen guys surfing in 5'er's with a 12 second period? I'm just sayin'...

Sorry if the above's a little harsh. But I ain't sure how to lay the reaility of it out any other way. And as a famous sailor once said: "The sea has little mercy. The rocks, none at all".

... But, on the other hand, sometimes a good knock on the head helps to reinforce the reality of the situation. To clarify further, water line to deck is only 3 feet, and tides are 3 feet, so 6 feet extra would seem what we need to compensate for only those factors. We are not going anywhere immediately and are in a bay that is very protected (from swell) but is very windy at present. Will increase the rode and consider moving the boat where we could let out more line.

Thanks,

G2L

[barnakiel]

Originally Posted by AD28

(...)

That said, don't touch a Bruce/claw with a 20' pole. In the 'emergency set' situation a boat which was (not) laying to a Bruce drifted down on me, the only one in the anchorage who came off his hook. Bruce. Not even once.

(...)

Arggghhhh. OK. That was one case. You cannot make very strong judgements about an anchor type from one observation. There are so many other elements: the bottom, the rode, the scope, the boat, the nut that holds the wheel ...

We have been using Bruces nearly since we started cruising (we converted from a CQR). We used to have a 22 pound copy Bruce during our rtw where we anchored hundreds of times in all possible bottom types. For our West Indies stunt two winters ago we upgraded to a true 35 pound Bruce (and we degraded our chain from 10 mm to 8 mm). The new setup seems to be even better.

The only times we could not anchor well with Bruce was over thick seaweed (kelp?). And we only ever dragged once (thin sand over rock shelf).

So, in my book, a Bruce is a fine hook. Except that possibly one can have a lighter modern style anchor to achieve the same result (say a Spade, a Brugel, a Rocna, etc.)

b.

[Gone2long]

Originally Posted by barnakiel

I would consider 35 pounds VERY light. We have a 35 pounds anchor in a 26 ft boat with only 2 ft of topside height and a most moderate displacement.

Unless your anchor is but a lunch hook, go for one that will let you sleep well no matter what.

b.

Thanks mate. Heavier and or better seems to be the consensus here.

Will contemplate all the above.

Regards,

G2L

[Gone2long]

Originally Posted by Xlantic

According to this site, a trimaran will have more windage than a monohull but less than a catamaran.
Forces

Thanks, will check it out.

G2L

[Gone2long]

Originally Posted by Stu Jackson

Why NEW GEN Anchors are Better:

Anchors & TEST Results of New Generation Anchors EXCELLENT & Important

Anchor System Sizing Tables (Reply #6) & Why Swivels are a bad idea Ground Tackle & Anchor System Sizing TABLES & Swivels

Thanks for the links.

G2L

[Xlantic]

Originally Posted by morven55

Are you saying that all the oil rigs that use the Bruce anchor are using the wrong anchors?
After all, what would the guys working oil rigs know about heavy seas?
All the same I will keep my 30kg Bruce [storm anchor] for my 10 ton boat, just in case...

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.

[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!!!