Conachair
Guest
F3 isn't strong wind, the comments about the catinery dissappearing were refering to more extreme conditions.
F3 isn't strong wind, the comments about the catinery dissappearing were refering to more extreme conditions.
noelex
Well-Known Member
There is no need to measure the forces, just look how the boat behaves when the wind swing through 180 degrees while you are anchored. The GPS will show the boat swinging around dragging all the chain until the chain is lying in the new direction. The anchor is the only bit that is fixed. The chain has not held the boat at all.
The force of wind to completely straighten out the chain in the new direction varies a bit depending on the bottom structure, but it happens at light to moderate winds typically 15-25K.
If the anchor was not there at all the one end would be unfixed and the boat would move in even lighter winds.
A practical example I was woken a couple of years ago by the anchor alarm. The anchor was still there, but it was completely unset because the anchor trip line had caught around my stern ladder. The chain and dead weight of the anchor could not hold the boat (broadside) in winds that were only about 10k. I had 50m of 13mm chain out on a 47 foot boat.
Another indication of the poor holding power of chain alone is to look at boats dragging. If the anchor becomes unset they will drag quickly in only moderate winds, imagine how poor the chain alone would perform without any resistance at all from the anchor.
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Mark-1
Well-Known Member
Nobody disputes that anchors rather than chain takes weight in strong winds. The dispute is about the light stuff, specifically F3.
rogerhudson
Member
Kobra anchor in Croatia
Does anyone know where in Croatia I can buy a Kobra2 anchor?
The chandlers around here are pathetic, anchorplait rope anyone?
Does anyone know where in Croatia I can buy a Kobra2 anchor?
The chandlers around here are pathetic, anchorplait rope anyone?
rogerhudson
Member
Just try to buy a Kobra2 in Croatia though, even the best chandlers in Split has less choice than found in a small Cornish seaside town.
rogerhudson
Member
Yes, it is the weight that is most important in Croatian anchorages, 45kg is far more than some 'experts' recommend for a 45ft boat.
You must have a very good windlass.
You must have a very good windlass.
Gallant Spirit
Well-Known Member
We find Rocna ok maybe scope 8:1 then slow astern to dig in then reduce to normal scope if busy anchorage
1bobt
N/A
This is another old thread resurrected ?????????????????????????????????????????????????/
RichardS
N/A
AMCD300
Well-Known Member
Vyv,
This is a very interesting article - thank you for sharing it.
I thought some very significant points came out:
(Quoting from Peter Smith website: http://www.petersmith.net.nz/boat-anchors/catenary.php)
- A rode consisting of 100% chain is neither desirable nor necessary.
- The catenary from the chain is often assumed to be a good shock absorber, in addition to lowering the angle of pull on the anchor, as it takes some time to straighten. However, this is a fallacy, as this quasi “spring” disappears in bad conditions when it is most needed. A proper shock absorber is a nylon snubber or similar.
- While catenary begins to become more important [in deeper water], scope remains king.
- The larger the boat, the more focus does need to be placed on the rode, particularly chain. Conversely, the smaller the boat, the more focus needs to go on the anchor (and providing good shock absorption).
- In the 2006 testing conduction by West Marine in association with SAIL magazine, the Rocna 15 (33 lb) held 4,800 lb-force at only 5:1 scope. The testers used 20′ of 5/16″ chain, the rest of the line 1″ nylon, in about 25″ of water, and reported the rode “bar tight”. In other words, such an anchor will not be troubled by weather conditions which easily eliminate the contributions of catenary to the angle of pull on the anchor. The “window” in which catenary does have some benefit is well below the ultimate limits of the anchor’s capability.
We might conclude that chain is entirely pointless, and 100% rope may be used. In theory there is some truth to this. However, chain is used with anchors for several other good reasons. These include abrasion resistance on the seabed and chaff resistance on the boat, the minimization of swinging circles in light conditions, and the dampening of a boat’s tendency to “sail” at anchor. However, rather than use very heavy chain, it is reasonable to use lighter chain which still meets strength requirements. A considerable amount of weight can be saved by using high tensile chain as opposed to regular BBB, hi-test, or G40.
- ...the benefit of catenary is mostly lost in strong winds, with the exception of very deep water, and since the anchor is probably quite capable of holding given an adequate angle of pull, the sole remaining thing you can do to help the anchor is veer more rode. If you want to increase the potential holding power of your system for the same scope, then the answer is to put the focus back on the anchor. If you have adequate scope deployed yet your anchor tends to drag, consider upgrading to a superior modern design. At the same time you could also increase the size of the anchor. Taking a few kilograms of weight out of the chain and putting it into the anchor results in a significant increase in holding power.
As you said, the anchor is where it is mostly happening, the rode and catenary helps take the load off the anchor and the angle of attack of the chain.
Good Sunday reading. Thank you
Andy
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D
Deleted User YDKXO
Guest
Not necessarily true. We do our boating in Croatia; we have a 53ft motorboat with a 40kg Delta and 70m of all chain rode. You will know how much motorboats swing at anchor due to their much larger windage than sailing boats. I often snorkel out to observe how well our anchor is set and I am always surprised how little movement there is in the chain that is lying on the sea bed even in windy conditions. At least with our boat, it seems only the first few metres of chain on the sea bed moves at all in response to the boat swinging. I am convinced that the weight of the chain itself and the frictional force which resists movement of the chain on the sea bed play a significant part in the holding power of the anchor and chain system.
Btw, I am a big fan of the Delta anchor. We have boated in the W Med as well as Croatia and the Delta has never let us down, unlike Bruce anchors
1bobt
N/A
Not wishing to start a new thread .
I have a 26kg Delta anchor and as most of you know its plough shaped. In all honesty I have had no problem with it, in fact I have another of the same size that I couple to the first in a big blow.
It has occurred to me that it shape is designed to plough in.. And I have considered having steel shoulders welded on to the sides of the anchor about 20cm from the point at an opposite angle to try and prevent it ploughing through the bottom .I can easily weld these shoulder on as I have all facility's to do so...
Only wondering if it would make any difference?
I have a 26kg Delta anchor and as most of you know its plough shaped. In all honesty I have had no problem with it, in fact I have another of the same size that I couple to the first in a big blow.
It has occurred to me that it shape is designed to plough in.. And I have considered having steel shoulders welded on to the sides of the anchor about 20cm from the point at an opposite angle to try and prevent it ploughing through the bottom .I can easily weld these shoulder on as I have all facility's to do so...
Only wondering if it would make any difference?
noelex
Well-Known Member
Most boats swing the chain in around 15-25k. If the chain was not fixed at one end by the anchor the holding power of the chain alone is less again, more like 10k will see the boat drag.
There are exceptions such as chain jammed under rock and in weed (which is common in Croatia) the wind speeds tend to be towards the higher level, but at these low wind speeds the forces are minimal and the security of the anchoring gear is not in question.
Around 25k is where an unset or very poorly set anchor will drag.
There are exceptions such as chain jammed under rock and in weed (which is common in Croatia) the wind speeds tend to be towards the higher level, but at these low wind speeds the forces are minimal and the security of the anchoring gear is not in question.
Around 25k is where an unset or very poorly set anchor will drag.
noelex
Well-Known Member
Concave anchors have certainly been more successful than the older convex alternatives.
I have a friend that modified his CQR in the way you describe and he has managed to improve the performance considerably.
However the Delta is reasonable performing anchor and modifications unless carefully done with a lot trial and error risk making the anchor performance worse. I would not do it.
If the Delta is old with worn galvanising you could consider sharpening the leading edges. This improves the performance especially in difficult substrates. However, it is hard to keep galvanising or paint on the sharper edges so life of the anchor suffers.
Jamesuk
Well-Known Member
40kg Lewmar Delta 300 drops in Adriatic, problem in silt and problem on flat bottom rocks (although all anchors would struggle with the latter)
The bruce is a bruce, it will be fine. If your worried there is always the marina for you MOBOs ;-))
The bruce is a bruce, it will be fine. If your worried there is always the marina for you MOBOs ;-))
D
Deleted User YDKXO
Guest
Yeah I'd be very interested in an anchor that sets in rock
The Bruce is indeed a Bruce and in my experience that means it won't penetrate a hard or weedy seabed. We had a couple of bad experiences in South of France anchorages with a Bruce. Of course, if it does get a bite, it has a lot of surface area and therefore can develop high holding power. IMHO, a Delta is a better all round anchor for a wider variety of conditions but I know discussions about anchors can often get heated so I say this is just my personal opinion
oldvarnish
Well-Known Member
Somewhat OT, so apologies, but my excellent Manson Supreme (20kg) is on the For Sale board. It would look lovely on a Croatian seabed.
BrianH
Well-Known Member
I completely agree. The last time I used a Bruce was in the anchorage between the islands of Ugljan and Pasman, about 6nm SE of Zadar. I tried everything short of diving with a shovel to set it in, but no, it just sat on the sandy surface and slid over it as the boat drifted back in the brisk wind. The embarrassing thing was that others arrived and tipped their assorted ironmongery over and dug in immediately. I eventually resorted to the backup Danforth and it held first time.
The problem seemed to be a thin covering of grass that the blunt,curved tip just didn't penetrate. I never used the Bruce ever again and stayed with the Danforth until I changed boats. It is again my backup but never needed as the Rocna has never (yet) failed me.
