Anchor test in chesapeake mud - bit of a surprise
- Thread starter dylanwinter
- Start date
I think it would be fair and have some statistical significant to suggest that those anchors that achieved a hold of 600lbs or less were poor and over the 5 pulls in different locations were consistently poor. None of these anchors (holding 600 lbs or less) ever showed any indication that they could be considered reliable in the seabed type chosen. For those that developed a hold greater than 600lb (excluding the Danforth and Fortress) had variable hold in the chosen seabed, sometimes poor, sometimes better - but they were inconsistent. Statistically they look unreliable, you might be lucky, who wants to rely on luck. The Danforth and Fortress at 32 degrees were reliable, over the 5 pulls, but did not develop a sufficient hold to engender a decent nights sleep (if the wind was to pick up). The only anchor to develop any degree of reliable hold was the Fortress at 45 degrees - and that was the point of the tests - I doubt Fortress have an axe to grind over other designs.
The consistency and reliability of the Fortress in mud seems to be echoed by people posting consistently on this thread.
There is an issue of changing the fluke angle, of the Fortress, but that does not seem such an issue if it means you sleep well. I am surprised that Fortress have not recommend we buy 2 anchors, one set at 32 degrees and one set at 45 degrees - it would solve the inconvenience
An anchor that is difficult to retrieve, the second post and others, is unlikely to trip in a change of tide. The Chasapeake tests demonstrated that when the Fortress was well set then the load developed was similar to the load needed to retrieve it (when the chain was being pulled vertically). This is not surprising, when the anchor is set and chain deployed the fluke angle to the seabed is 45 degrees. When the Fortress is to be retrieved, the fluke angle is 45 degrees. If well set it does not seem it would trip.
I am not sure what level of statistical significant is required but when an anchor does not set, at all, in 5 times out of 5 but other anchors do set then I would tend to say that the anchor(s) not setting (developing a hold less than 600lbs) are not designed for that seabed. I think to suggest that 5 times out of 5 failures (or even 3 failures out of 5) lacks statistical significance is trying to guild a dead lily. We need a bit more certainty and the Fortress and to a lessor extent the Danforth offered that certainty - which would be increased (the certainty that is) if decent snubbers were used.
I agree having time to set in mud is useful - but sometimes we do not have that amount of time, it gets back to the certainty issue.
Jonathan
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Joker,
When you add your weight allow it to drag on the seabed. You will still get the catenary effect you desire but the weight will also act as a friction break, and dampen the yawing. I'd recommend Dylan's solution, use a second anchor as an angel. You will be carrying a second anchor anyway(?
) and it allows you to use it to best advantage, being of a different design it will be more useful in different seabeds, if you lose your first you have something to fall back on and it can be an angel (heavily disguisedJonathan
lw395
Well-Known Member
I'd think twice about that with a rope rode, as anchors tend to have fairly sharp bits which might damage the rope.
Unless you are making sure the kellet stays off the seabed.
Any kellet on the seabed can see a lot of chafe in a short time.
An iron gym weight seems a good idea, handling two anchors on the foredeck if you decide to leave in a hurry might not be easy.
jimbaerselman
Well-Known Member
A few points to add to the discussion:
(1) A change in the angle of pull at the anchor of more than 60 degrees creates a strong likely-hood of breakout, followed by a re-set.
(2) pull angle changes are caused by tidal stream reversals, strong wind "sailing" to a single anchor, and wind direction changes.
(3) All flat anchors (danforth, fortress, britany) behave well in soft mud as long as sufficient scope is allowed (much less scope for high angle fortress, but up to x6 for others) since with long scope they will just bury ever deeper. However, they all fail the change in angle test . . . will pop out and have to re-set.
(4) Many "more modern" anchors are more tolerant of changing angles of pull
(5) Re-sets are always a risk - almost all anchor designs can occasionally clog up with weed, debris or even their own rode
(6) tidal reversal or major wind change is only reliably survived by using a running moor
(7) "sailing" at anchor (if your boat is prone to it) will not cause angle of pull shifts if you use a forked moor
Yes, I know twin anchors are a PITA. And I know the rest of the guys around you may not have two anchors out.
(8) maximum stresses at the anchor are caused not by wind drag, or tide stream strength, but by the snatch when a boat which sails at anchor is tacked, or if there's a big pitching seaway
(9) catenary does little to reduce snatch forces in both above cases - which questions the utility chums or kellets too. Far more effective is up to 40m of nylon snubber, giving 4m of elasticity. That really softens the blow . . .
So, single pull tests may give you data with +/- 20% confidence. But the factors above (and I've left out the bottom, and selection of scope!) provide a lot more variation in the forces which will be applied to the anchor. Reduce those, and you can even survive using a fisherman and CQR.
If you can find the space to deploy them!
(1) A change in the angle of pull at the anchor of more than 60 degrees creates a strong likely-hood of breakout, followed by a re-set.
(2) pull angle changes are caused by tidal stream reversals, strong wind "sailing" to a single anchor, and wind direction changes.
(3) All flat anchors (danforth, fortress, britany) behave well in soft mud as long as sufficient scope is allowed (much less scope for high angle fortress, but up to x6 for others) since with long scope they will just bury ever deeper. However, they all fail the change in angle test . . . will pop out and have to re-set.
(4) Many "more modern" anchors are more tolerant of changing angles of pull
(5) Re-sets are always a risk - almost all anchor designs can occasionally clog up with weed, debris or even their own rode
(6) tidal reversal or major wind change is only reliably survived by using a running moor
(7) "sailing" at anchor (if your boat is prone to it) will not cause angle of pull shifts if you use a forked moor
Yes, I know twin anchors are a PITA. And I know the rest of the guys around you may not have two anchors out.
(8) maximum stresses at the anchor are caused not by wind drag, or tide stream strength, but by the snatch when a boat which sails at anchor is tacked, or if there's a big pitching seaway
(9) catenary does little to reduce snatch forces in both above cases - which questions the utility chums or kellets too. Far more effective is up to 40m of nylon snubber, giving 4m of elasticity. That really softens the blow . . .
So, single pull tests may give you data with +/- 20% confidence. But the factors above (and I've left out the bottom, and selection of scope!) provide a lot more variation in the forces which will be applied to the anchor. Reduce those, and you can even survive using a fisherman and CQR.
If you can find the space to deploy them!
There are no hard and fast solutions and nothing is set in concrete. Its all about offering different solutions to the same problems allowing the individual to pick and choose.
I'm not sure that handling a gym weight or an anchor of the same weight have much to choose between them if you are in anything of a hurry
But if you pursue the gym weight idea - put chain through the hole in the weight and link with a small shackle, then find a large stainless shackle (which will be smooth and polished) and run the rode through that. The shackle will be attached to the chain loop. If you use a second anchor, use the same large stainless shackle - it will allow the rode to run freely, is easy to attach and will minimise chafe.
But using a second anchor as a means to stop yawing is an ancient practice and was used by the RN. I recall the practice was not to use as a kellet but simply dropped off the bow, independent of the rode, it simply drags on the seabed. As it is on a short scope, sufficient to keep the dropped anchor on the seabed at high tide, it does not set - just drags (and dampens veering).
Jonathan
edit And if you dampen veering you minimise those snatch loads mentioned in post #25. end edit
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noelex
Well-Known Member
The Fortress adjusted to a 45 degree fluke angle is really outstanding in soft mud. I don't think anyone was suprised by its performance.
As Estarzinger has mentioned the overall results of this test are highly variable which makes meaningful conclusions about other anchors impossible to deduce. If you assume normal distribution (which is not quite correct) the standard deviation for the Fortress results in this teat at 45 degrees are over 800 lb ! Mean results are not very significant with such a large data spread. Unfortunately this high variability is a consequence of limited trials in a very difficult substrate. Fortress should be given kudos for trying. Most of the anchors, Including the Fortress, failed to set in at least one of the five trials.
The recorded "holding power" was very low even for the Fortress at 45 degrees indicating it must have been a very soft substrate. It is misleading to call these results "holding power" none of the anchors were holding. They were all moving backwards at a reasonable rate as part of the test protocol. The actual holding power (the maximum force without the anchor moving) would be lower.
Even ignoring this, the average holding power translates to a low wind speed unless the Fortress was considerably oversized.
The holding power of any of the anchors was not adequate for safe overnight anchoring.
This is a study where you need to look at raw data. The high variability in the test is obvious without resorting to any statistical tools. The results can be found here:
http://fortressanchors.com/wp-content/uploads/2014/11/Chespeake-Bay-Anchor-Test-Aug.2014.pdf
Fortress is an excellent anchor. Its is very lightweight which combined with its high holding power makes it the premier choice as secondary/kedge/stern anchor. I have one and would highly recommend it in this role. It also has outstanding holding power in soft substates especially set at 45 degrees (but don't use this setting unless you are positive the substrate is very soft. The anchor will not work at all at 45 degrees in most bottoms.)
However, the Fortress has got some limitations, which reduce its suitability as a bower anchor. As others have mentioned the tendency for the Fortress (and Danforth anchors) to occasionally completely breakout if the direction pull is changed needs to be considered. The Fortress also drags very rapidly if it lets go.
As Estarzinger has mentioned the overall results of this test are highly variable which makes meaningful conclusions about other anchors impossible to deduce. If you assume normal distribution (which is not quite correct) the standard deviation for the Fortress results in this teat at 45 degrees are over 800 lb ! Mean results are not very significant with such a large data spread. Unfortunately this high variability is a consequence of limited trials in a very difficult substrate. Fortress should be given kudos for trying. Most of the anchors, Including the Fortress, failed to set in at least one of the five trials.
The recorded "holding power" was very low even for the Fortress at 45 degrees indicating it must have been a very soft substrate. It is misleading to call these results "holding power" none of the anchors were holding. They were all moving backwards at a reasonable rate as part of the test protocol. The actual holding power (the maximum force without the anchor moving) would be lower.
Even ignoring this, the average holding power translates to a low wind speed unless the Fortress was considerably oversized.
The holding power of any of the anchors was not adequate for safe overnight anchoring.
This is a study where you need to look at raw data. The high variability in the test is obvious without resorting to any statistical tools. The results can be found here:
http://fortressanchors.com/wp-content/uploads/2014/11/Chespeake-Bay-Anchor-Test-Aug.2014.pdf
Fortress is an excellent anchor. Its is very lightweight which combined with its high holding power makes it the premier choice as secondary/kedge/stern anchor. I have one and would highly recommend it in this role. It also has outstanding holding power in soft substates especially set at 45 degrees (but don't use this setting unless you are positive the substrate is very soft. The anchor will not work at all at 45 degrees in most bottoms.)
However, the Fortress has got some limitations, which reduce its suitability as a bower anchor. As others have mentioned the tendency for the Fortress (and Danforth anchors) to occasionally completely breakout if the direction pull is changed needs to be considered. The Fortress also drags very rapidly if it lets go.
lw395
Well-Known Member
Fair comment.
First understand exactly what problem you're trying to solve.
One place I go, the bottom is mud with stones in.
It is incredibly abrasive, I'd not want a rope rode dragged across that all night.
Also, to put the article in context, a force of 500lb will be plenty for a lot of boats in 'every day' anchoring.
GHA
Well-Known Member
Ta for the link, paints a very different picture.
ffiill
Well-Known Member
Why a suprise?
When someone is hammering you with machine guns and artillery you need that anchor attached to your stern pull off winch to get your landing craft off that beach.
The Danforth was designed to do just that and therefore not suprising that its evolved form remains good at it.
When someone is hammering you with machine guns and artillery you need that anchor attached to your stern pull off winch to get your landing craft off that beach.
The Danforth was designed to do just that and therefore not suprising that its evolved form remains good at it.
Brian@Fortress
Well-Known Member
Noelex, in the link you posted, you will note that during two pulls the 21 lb / 10 kg Fortress FX-37 @ the 45° angle achieved tensions which were still climbing above 2,000 lbs when the test was ended. In another pull, the tension reached 1,800 lbs early on before falling back to over 1,000 lbs at the end, indicating that the anchor did not disengage from the bottom.
In one other test, the tension was rising about 800 lbs at the end of the test, and during one pull the FX-37 did not set.
By contrast, the 44-46 lb (20-21 kg) anchors rarely exceeded 1,000 lbs during this testing and typically when they did, they quickly broke free from the soft mud bottom and did not re-engage. In 3 out of the 5 tests, two of these anchors did not even achieve a 300 lb tension.
One test result that was not widely reported by several of the magazines who had writers aboard was that of the 10 lb / 4.5 kg FX-16, which was not in the original test protocol and it was deployed after almost 4 full days of testing and 60 total tests. At the 45° angle this anchor achieved tensions that exceeded 1,500 lbs, far more than any of the 44-46 lb (20-21 kg) anchors, and comparable to the FX-37 @ the 32° angle and the 35 lb (16 kg) Danforth HT.
Afterwards this anchor was one of the most difficult to get back out. Video from that 4th day is at the link below, and the FX-16 testing is at the 8:00 minute mark.
https://www.youtube.com/watch?v=4Ga1_LCZ90g
Videos from each day of the testing can be found at that YouTube channel as well.
Safe anchoring,
Brian
In one other test, the tension was rising about 800 lbs at the end of the test, and during one pull the FX-37 did not set.
By contrast, the 44-46 lb (20-21 kg) anchors rarely exceeded 1,000 lbs during this testing and typically when they did, they quickly broke free from the soft mud bottom and did not re-engage. In 3 out of the 5 tests, two of these anchors did not even achieve a 300 lb tension.
One test result that was not widely reported by several of the magazines who had writers aboard was that of the 10 lb / 4.5 kg FX-16, which was not in the original test protocol and it was deployed after almost 4 full days of testing and 60 total tests. At the 45° angle this anchor achieved tensions that exceeded 1,500 lbs, far more than any of the 44-46 lb (20-21 kg) anchors, and comparable to the FX-37 @ the 32° angle and the 35 lb (16 kg) Danforth HT.
Afterwards this anchor was one of the most difficult to get back out. Video from that 4th day is at the link below, and the FX-16 testing is at the 8:00 minute mark.
https://www.youtube.com/watch?v=4Ga1_LCZ90g
Videos from each day of the testing can be found at that YouTube channel as well.
Safe anchoring,
Brian
oldvarnish
Well-Known Member
Well that should wind up the Rocna camp!
Let me do it for them
http://www.petersmith.net.nz/boat-anchors/independent-performance-testing.php
If the seabed has stones in it (or is abrasive) and is the seabed in which you regularly anchor I'd be using all chain.
500lb tension is about 25kn wind at 5:1 on a 45' yacht. All of the chain will be lifted (assuming a 'normal' amount of chain.
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All tested in sand - no word of warning that the results in sand will not be repeated in mud.
Noelex is an excellent example - if you want to market an anchor and demonstrate its good points - test in sand and whatever you do - do not test in mud or weed.
noelex
Well-Known Member
When the forces were measured In the Fortress test the anchor was not stationary.
The Fortress test measured dynamic holding capacity (DHC). In other words the force measured when the anchor was being pulled through the substrate. Obviously to be "anchored" the anchor has to be stationary. This is known as the static holding capacity (SHC).
It is wrong to refer to DHC as the holding capacity of the anchor. To anchor successfully the anchor has to be stationary. The SHC.
We need to convert the DHC measured by the Fortress test into the SHC that would hold our boat stationary. SHC is less than DHC. Professor Knox has done some work on this subject. At the 5cm/sec that the Fortress test was conducted the conversion rate is 0.24.
So the actual force the anchor would hold without moving is about 1/4 of the force measured when the anchor is moving at 5cm/sec.
Professor Knox's conversion formula was determined in sand rather than soft mud. There is no conversion factors available for mud.
The mean DHC capacity of the Fortress set at 45 degrees, is already low. It translates to continually moving at 5cm/sec and letting go in about 27 knots wind for the recommended size boat. Of course moving at 5cm/sec (30m in 10 min) before letting go is not acceptable. Converting the windspeed where the anchor would not move (the SHC) would give a lower windspeed.
noelex
Well-Known Member
No I have a Fortress anchor. I have used a Fortress for many years (as a secondary anchor). I also have a small Guardian anchor for my tender.
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NormanS
Well-Known Member
Remember that back in the real world, a boat does not exert a steady pull on an anchor, so an anchor "test" by applying a constant pull is in no way replicating the normal loading on an anchor. In my own experience, we often get strong, but gusty winds. With a relatively heavy boat, I often find that the boat reacts quite slowly to the gusts, and often by the time the chain threatens to get anywhere near straight, the gust has died a bit.
I note you are critical of the performance of the Fortress and studiously ignore the performance of the other anchors. Frankly I would rather be using an anchor that operates upto 27 knots than one that does not operate at all as a decent snubber will allow the Fortress to perform at higher wind speeds, as NormanS describes in post #38
I think you need to know the relationship between SHC and DHC in mud before you make any comments - your knowledge is at best superficial and is incorrect.
This is a very brief summary of a comment from someone who worked on anchors for the Navy and Offshore Oil industry all of his working life
quote
• The Navy and offshore industry have been installing and proofing anchors for many years and I have not seen anything that suggests that true anchor capacity should be reduced according to Knox’s findings. Anchors are loaded to a proof set target and held for a certain amount of time and as long as load doesn’t drop beyond an accepted target due to soil consolidation or creep after an industry accepted period of time then the anchors are accepted as satisfying the design target. We use factors of safety to account for uncertainty.
end quote
Professor Knox is measuring consolidation and creep in his specific seabed, nothing more and to apply his findings to another seabed, especially one that is mud is wrong. Fully saturated mud and sand behave totally differently. If he had held his anchors under full load for longer the creep and consoldiation would have stopped and he would then have found that his SHC and DHC were one and the same.
As far as I am aware no-one but John Knox (and yourself) has proposed this factor between SHC and DHC and not one set of anchor holding power tests makes any mention.
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noelex
Well-Known Member
This quote you posted was from part of an email written by Bob Taylor who is a consultant for Fortress. The email was to answer questions I personally posed to Fortress about their adjustment for DHC verses SHC.
I am curious how you got hold of a copy. I assume you have not read my email to Fortress posing the questions that prompted Bob's response. I would imagine the email does not really make sense without this.
I basically agree with Bob's view (if you have read the whole email) that Professor Knox's coefficients to convert DHC to SHC are not appropriate for mud. If they were we would need to multiply the Fortress results by 0.24 to translate them to true holding capacity values. This would convert the already low results to ridiculously low values. However, it is also self evident that the force measured when the anchor is moving at a considerable speed (for an anchor
) is not the same as the "holding power". As the force is reduced the anchor will stop moving.This in no way invalidates the test, but it does mean the true "holding power" is lower than indicated.
This should not obscure the fact that the Fortress, as expected, did exceptionally well, but this together with the low and inconsistent results, even for the Fortress, further indicates that this substrate was too soft for overnight anchoring.
Fortress have selected, as you would expect, a very soft substrate to show the superiority of their anchor, especially when adjusted to 45 degrees. In hindsight a slightly firmer substrate would have likely revealed far more consistent results and allowed a meaningful analysis of the other anchors' performances.
Fortress and Danforth anchors have very high holding power in soft substrates, providing the pull is in a reasonably constant direction. I have no doubt they would still have won.
