Fork or 'V' anchoring
- Thread starter Neeves
- Start date
NormanS
Well-Known Member
I'm not saying that you need a bigger anchor. All I'm saying is that some anchor makers base their size/weight recommendations on 30 knots of wind. You can draw your own conclusions. I KNOW that there will be times that my boat WILL be anchored in greater wind strengths, and so I equip accordingly.
thinwater
Well-Known Member
Fortress presents an interesting case, specifically in firm bottoms. I did a lot of anchor testing with both large and small anchors.
If I set a Fortress FX-16 off my 34-foot catamaran with 20 hp in firm sand I will just bury the flukes. This is the recommendation for 30 knots. For a storm they recommend a 23 or 37. The setting force available is about 275 pounds, and the probable 60-knot storm load is about 1200 pound with the bridle I use. If I set a 23 the shank won't even be on the bottom and with a 37 the tips will just be in. A child could lift the 37, the 23 will trip if I bump it at all, and the 16 may come out if the wind shifts hard.
On the other hand, I set a Guardian G-4 (same dimensions, price-point version) with 400-750 pounds in the same location several times. I thought I was going to loose it several times, it was burried so deep. That little 2-pound anchor would have held a good blow in any direction, and certainly 30 knots would have been no challenge in that bottom. In fact, that is how I set it (30 knots, all chain, Dyneema snubber, lots of shock loading).
If a Fortress trips out of a sticky bottom (and to so some extend other anchors) there is perhaps a 15% probability it will reset. Normally the flukes are clogged and will not flop over.
So what does this tell us?
a. The holding capacity of Fortress anchors in good bottoms is quite a lot.
b. In firm bottoms they are not secure in a wind change unless well set. An over-sized, or even conservatively sized anchor cannot be well set with the power available to many sailboats.
c. They are a bugger to recover if deeply set.
I'm not sure this applies to other anchors. It does not apply to A Fortress that is set in a wide V, since the angle will not change that much. But it is interesting. It leads to an important question for NG anchors, which I will not try to answer. Is it better to set the anchor deep, or to leave it near the surface so it can more easily rotate when the wind shifts? With nice sand the latter may be true. With soft mud, full of trash as it often is, I'm not at all sure I want the anchor moving much.
Personally, I can't favor the wisdom of going big with a Fortress unless it is for real storm (hurricane) anchoring in really soft mud. It may actually be less secure, though it will be easier to recover. On the other hand, I never use a Fortress in a way with the angle of pull will change much. Remember also that Fortress is made in soft mud country, so that colors their thinking.
If I set a Fortress FX-16 off my 34-foot catamaran with 20 hp in firm sand I will just bury the flukes. This is the recommendation for 30 knots. For a storm they recommend a 23 or 37. The setting force available is about 275 pounds, and the probable 60-knot storm load is about 1200 pound with the bridle I use. If I set a 23 the shank won't even be on the bottom and with a 37 the tips will just be in. A child could lift the 37, the 23 will trip if I bump it at all, and the 16 may come out if the wind shifts hard.
On the other hand, I set a Guardian G-4 (same dimensions, price-point version) with 400-750 pounds in the same location several times. I thought I was going to loose it several times, it was burried so deep. That little 2-pound anchor would have held a good blow in any direction, and certainly 30 knots would have been no challenge in that bottom. In fact, that is how I set it (30 knots, all chain, Dyneema snubber, lots of shock loading).
If a Fortress trips out of a sticky bottom (and to so some extend other anchors) there is perhaps a 15% probability it will reset. Normally the flukes are clogged and will not flop over.
So what does this tell us?
a. The holding capacity of Fortress anchors in good bottoms is quite a lot.
b. In firm bottoms they are not secure in a wind change unless well set. An over-sized, or even conservatively sized anchor cannot be well set with the power available to many sailboats.
c. They are a bugger to recover if deeply set.
I'm not sure this applies to other anchors. It does not apply to A Fortress that is set in a wide V, since the angle will not change that much. But it is interesting. It leads to an important question for NG anchors, which I will not try to answer. Is it better to set the anchor deep, or to leave it near the surface so it can more easily rotate when the wind shifts? With nice sand the latter may be true. With soft mud, full of trash as it often is, I'm not at all sure I want the anchor moving much.
Personally, I can't favor the wisdom of going big with a Fortress unless it is for real storm (hurricane) anchoring in really soft mud. It may actually be less secure, though it will be easier to recover. On the other hand, I never use a Fortress in a way with the angle of pull will change much. Remember also that Fortress is made in soft mud country, so that colors their thinking.
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zoidberg
Well-Known Member
I've never been convinced by the 'more weight is better' argument, for once an anchor is set, the weight becomes irrelevant. More weight may have relevance to causing the flukes or point to commence to dig in but IMHO not after that.
What seems to me to be more relevant to the 'holding power' of an anchor is the area/volume of that chunk of seabed it has buried itself into, modified by the resistance of that chunk of seabed to being ploughed more or less horizontally.... the'ooziness' factor.
I once owned a heavy ( 65lb ) Folding Fisherman anchor designed by Ian Nicholson. When set, it had but one fluke embedded - an area broadly equivalent to the smallest of Fortress/Danforth types ( an order of magnitude lighter ). I suppose it would have earned its keep in rocky kelp-ridden anchorages in the far North West... but not around the Isles of Scilly or Falmouth Roads.
What seems to me to be more relevant to the 'holding power' of an anchor is the area/volume of that chunk of seabed it has buried itself into, modified by the resistance of that chunk of seabed to being ploughed more or less horizontally.... the'ooziness' factor.
I once owned a heavy ( 65lb ) Folding Fisherman anchor designed by Ian Nicholson. When set, it had but one fluke embedded - an area broadly equivalent to the smallest of Fortress/Danforth types ( an order of magnitude lighter ). I suppose it would have earned its keep in rocky kelp-ridden anchorages in the far North West... but not around the Isles of Scilly or Falmouth Roads.
Neeves
Well-Known Member
Yes you do need to prove that doubling weight doubles hold. It can be discarded as nonsense - it is up to the individual to come to their own conclusions. Gut feel offer support to the argument but there is sufficient evidence to question any conclusions and sufficient evidence to cast doubts.
Personally I err on caution and don't gamble with other people's assets and lives.
Prof Knox tests were conducted with different rodes of different elasticities.
If you do not think rodes matter, or catenary, or elasticity - please explain?
With all the resource available to the oil industry the best they can achieve is UHC = 0.92W - Knox shows something like (from memory) UHC = 2W - with work from gifted amateurs - please get real. Find any other evidence!
Find me an anchor maker of 'our' anchors who claims doubling anchor weight will more than double hold - I can assure you - if this was possible they would have said so! - its a fundamental marketing advantage - guess why they have not made the claim. Check the formula for Bruce, sadly Prox Knox data and data from Bruce, Vryhof, US Navy is at variance. Dig deeper, maybe it is more complex than rocket science.
Fortresss returns a relationship in thin mud of UHC = 0.83W
Hold is a function of yacht windage - you do not magically increase the hold developed by using a bigger anchor. A yacht in a wind developing a hold on a 20 kg anchor of 400kg will develop a hold on a 30kg anchor of 400kg and a hold on an anchor of 40kg of 400kg and a hold on a concrete block of 1t of 400 kg. If the UTC of the anchor is 2t (equivalent to 60 knots) on the 20kg anchor - it will hold - there is no need for the 40kg anchor.
Edit
There is also some evidence suggesting that a larger anchor has disadvantages, a Post from both Thinwater and Vyv Cox - they raise questions. If there are questions there is need to 'waste time' 'proving' bigger is better - it might not appeal - but I for one see no reason to support the pension funds of anchor makers at my, or the forum members, expense.
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noelex
Well-Known Member
Jonathan, I am sure you understand enough engineering to know the irrelevancy of this argument.
It is like saying a car with a low horsepower engine and a car with a large horsepower engine are using the same power (assuming they are otherwise identical and ignoring minor internal friction differences) if they are driving down the road at the same speed. This is true, but it says nothing about the maximium top speed, which of course will be higher in the car with the higher horsepower engine.
The same applies to anchors. For a particular wind speed a yacht will exhibit the same force on large and small anchor, but if the wind speed is increased, at some point the force will exceed the maximium holding power of the smaller anchor (for that particular substrate and scope etc) and the anchor will start to drag. At this point the larger anchor (assuming all other things such as the model construcion material etc are equal) will not have reached its maximium holding power and the yacht lying to that anchor will not drag. As the wind speed increases further, at some stage the force will reach the point where the limit of the holding power of the larger anchor is reached and at this point the boat with the larger anchor will also start to drag.
If the wind speed does not reach the level where the ultimate holding power of the smaller anchor is reached (for that particular substrate and scope etc), everything is fine. If the limit is exceeded, the anchor and boat will drag. It is a simple concept.
As to the rest of your post, you previously asked for evidence that a larger anchor has a higher holding capacity than an otherwise identical smaller anchor. This should not even be a serious question, but nevertheless I have indicated studies from two well respected authorities, Professor Knox and Vryhof that have shown just that. Both even felt confident enough in the results to devise a formula to quantify the improvement. The only study you indicate to support your argument is from Fortress and thin mud but the formular you quote bizarrely shows quite clearly that as the anchor size is increased the ultimate holding if the anchor is also increased, in this case it shows doubling the weight increases the holding power by 1.66 times.
You seem to desperately want to believe that the small 15 kg steel (or 8 kg aluminium) anchors you use on your 38 foot catamaran have the same ultimate holding ability as equivalent larger models. Perhaps this helps you sleep at night, but it is not a view that is based on reality.
Now, I am sure everyone else is fiding this boring, so lets get back to some more sensible questions.
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dovekie
Well-Known Member
Just for info', a delta or v-shaped riding sailing has a far stronger stabilising effect than a flat one. This sort of thing:
Reduces veer by about two thirds, and we have flown one in 50 knots.
Apologies for the thread drift.
Neeves
Well-Known Member
Noelex,
As said you cannot test, as John Knox did, and then compare different anchors using different rodes of different elasticities for the tests. The results are meaningless and are not reflected in Vryhof or US Navy results. With an elastic rode some of the power of the winch is required to stretch the rode and this stretch (and power 'diversion' will increase with tension applied and not be used to set the anchor). With different rodes these 'losses' will vary.
Read the articles again - the rode types are clearly defined.
The Fortress results are a compilation of all the soft mud results produced by Fortress, who are the only company I know who have tested their full range of anchors. I think there are between 20 and 30 individual results. The results have been compiled by a leading consultant in the International anchor industry who worked with both Bruce, Vryhof and the US Navy. I apologise for discarding your information in favour of his. As you point out the results suggest doubling weight increases hold by 1.66 times - which is very different to your doubling weight doubles hold. I prefer to be cautious and work with the lower figure, not your unsupportable idea - that has no basis in fact. The 1.66 factor is also more in line with internationally accepted results for the bruce anchor - which can be as low as 1.4 times (depends on seabed).
The reason anchor size has been discussed is because a member of the forum asked the question, if you think his question not sensible maybe you could send him him a PM and let him know.
I don't need data to support our choice of anchors - they have proved themselves - there is no data to support your contentions. Carrying a mobile mooring around with you suggests a lack of confidence in your ground tackle
Jonathan
As said you cannot test, as John Knox did, and then compare different anchors using different rodes of different elasticities for the tests. The results are meaningless and are not reflected in Vryhof or US Navy results. With an elastic rode some of the power of the winch is required to stretch the rode and this stretch (and power 'diversion' will increase with tension applied and not be used to set the anchor). With different rodes these 'losses' will vary.
Read the articles again - the rode types are clearly defined.
The Fortress results are a compilation of all the soft mud results produced by Fortress, who are the only company I know who have tested their full range of anchors. I think there are between 20 and 30 individual results. The results have been compiled by a leading consultant in the International anchor industry who worked with both Bruce, Vryhof and the US Navy. I apologise for discarding your information in favour of his. As you point out the results suggest doubling weight increases hold by 1.66 times - which is very different to your doubling weight doubles hold. I prefer to be cautious and work with the lower figure, not your unsupportable idea - that has no basis in fact. The 1.66 factor is also more in line with internationally accepted results for the bruce anchor - which can be as low as 1.4 times (depends on seabed).
The reason anchor size has been discussed is because a member of the forum asked the question, if you think his question not sensible maybe you could send him him a PM and let him know.
I don't need data to support our choice of anchors - they have proved themselves - there is no data to support your contentions. Carrying a mobile mooring around with you suggests a lack of confidence in your ground tackle
Jonathan
Neeves
Well-Known Member
No need to apologise
The thread was about 'V' mooring which we use to reduce veer and to ensure each anchor is loaded in line with the direction in which the anchor was set. If there are other ways to ensure the same result - I for one see no reason not to explore them.
Zoidberg made the suggestion of using a windsurfer masts, one on each hull, to extend our transoms to allow use of a riding sail. Thinking of the idea further - maybe I'll try extending the boom aft with a windsurfer mast and attach a cross piece at the outer, aft, end. This will give me the spread for a 'V' shaped arrangement and I can tension the cross piece back to load bearing parts of the hull. I vaguely recall someone using a cross piece to secure a riding sail and someone else, Aussie Bray?, who had a short section of pole within his boom that he used as a davit to lift his dinghy - so the ideas are not new.
Jonathan
vyv_cox
Well-Known Member
I like the look of that but impossible on our boat unfortunately.
noelex
Well-Known Member
Thanks, Dovekie
No need to apologise. It is good to have more practical feedback from people experienced with using a riding sail.
Did you feel the overall drag of the sail had any significant impact on the force experienced by the anchor?
One other note for those thinking of experimenting with a riding sail, is make sure nothing can come loose if you have a wind generator. With a little bit of care this should not be a problem, but I have seen a couple of wind generators destroyed on cruising boats due to this, hence the warning.
fisherman
Well-Known Member
Sorry I haven't read this through, but there was a long discussion about this before. Setting two anchors in a vee reduces the holding power of both, its a vector thing dependent on the angle. Try this at home, get two heavy weights with a tight rope between, pull up in the middle, you can easily move the weights but as they come together it gets more difficult. If you veer from one anchor to the other you only get one x holding power at a time. The answer from the 'experts' was, if one anchor isn't enough, get a bigger one. In my case I had to anchor for a while in 60kt winds outside Porthleven, I used both anchors backed up, and that is what extra master Graham Danton recommends in his Manual of Seamanship.
Neeves
Well-Known Member
Can you explain - 'both anchors backed up'
There is no suggestion that 2 anchors in a 'V' allows the combined holding capacity of the 2. They reduce veering and each anchor individually holds the yacht alternately with its set direction being that of the relevant veer. So instead of veering and having one anchor loaded at an angle to its direction of set, first one side and then the other.
I our case there are no doubts on the hold of the individual anchors, we simply don't want to veer and we want to have the maximum tension on each anchor to be as close as possible to the set direction.
You really need to read the whole thread.
Jonathan
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Neeves
Well-Known Member
Noelex I really like your car analogy - but my interpretation it differently
Not entirely the best analogy - Its the house wife using the Porsche 4x4 to take the kids a kilometre to school each day, leaving the Ford saloon on the drive.
Jonathan
Not entirely the best analogy - Its the house wife using the Porsche 4x4 to take the kids a kilometre to school each day, leaving the Ford saloon on the drive.
Jonathan
vyv_cox
Well-Known Member
I think if you read it you will see that ultimate holding power is not the object of the exercise. Fork mooring reduces the yaw angle by a factor of 2+, improving comfort levels for those on board.
GHA
Well-Known Member
120 deg is the magic number between the rodes.
The force on B is shared between A1 & A2 so the "200" vector is actually 100 - less than 120° you can't get a greater load on either anchor.
vyv_cox
Well-Known Member
120 deg is the magic number between the rodes.
The force on B is shared between A1 & A2 so the "200" vector is actually 100 - less than 120° you can't get a greater load on either anchor.
That's assuming the boat remains static? It has never happened to me, the load transfers from one rode to the other constantly, quite mesmerising to watch. I have never attempted to get 120 degrees though, I aim for 60 - 90.
GHA
Well-Known Member
Looking just at the geometry, with 120 ° angle it's impossible for more load to go on one anchor than is created by the boat, doesn't matter which way the boat points.
I hardly ever use 2, but instinctively would go for a shallower angle.
fisherman
Well-Known Member
two anchors backed up=in line on the same rode. I seem to remember 120deg is the magic number, wider than that and the load on both anchors can be more than one boat's worth.
To demonstrate, tie a string to the doorknob, attach a weight to the middle. Pull the string tight, as it straightens the load on each end is increased until both loads are more than the weight lifted, when nearly straight the load can be many times the weight.
Indeed you can reduce yawing about, but it's not a valid way to increase overall holding, as the boat inevitably loads one side then the other.
To demonstrate, tie a string to the doorknob, attach a weight to the middle. Pull the string tight, as it straightens the load on each end is increased until both loads are more than the weight lifted, when nearly straight the load can be many times the weight.
Indeed you can reduce yawing about, but it's not a valid way to increase overall holding, as the boat inevitably loads one side then the other.
NormanS
Well-Known Member
With two anchors at 120°, and provided the rode is joined forward of the bow roller, is pretty much the definition of a Bahamian Moor. It has the huge advantage over rigging two anchors on the one rode, that the boat is secure in any wind direction, and swings in a very small circle. I have never tried "tandem anchoring" with two anchors on the one rode, but I would imagine that retrieval could be a nightmare, particularly in deeper water.
