Chesapeake Anchor Holding Power Test

[Marin]

Jonathan--- I think you've made a fair statement (your post #734). I think everyone would agree that no anchor will perform perfectly in every conceivable situation. Fortress' soupy mud test illustrates that.

When I say I think the Rocna design, or perhaps I should broaden that to the overall rollbar anchor concept, is the "best in the world," in my mind, at least, I am allowing for those situations where the design did not perform as well as others for various reasons.

But to me, if we say that a 95% success rate is what is experienced with the rollbar anchor family in all the conditions under which it is used, that'a a hell of an enviable success rate to my way of thinking.

You're in a position to hear a lot more about anchor performance than I am, but in my experience, observation, conversations, and reading, other anchor types don't seem to enjoy this same success rate.

I fully agree with the notion that if one is going to encounter anchoring conditions for which one's primary anchor is not very well suited, carrying an additional anchor that IS suited to these specific conditions is a smart move. Hence the Fortress FX-23 on our swim step.

Regarding Al and other's feelings about this overall thread, it would be interesting to know WHY anchors evoke such long and passionate discussions on forums like this.

My own opinion is that, like one's boat itself, an anchor is a chance for a boater to express his or her individuality. Like vehicles. I despise anything made by GM, others think GM is the only way to go.

Also, an anchor is a bit of mystery. It does its work unseen to the majority of us. And the unseen/unknown has always had a fascination for people, with a great deal of effort being put into speculating about it, and defending what one believes about it.

 

[Nomad Willy]

Marin I guess I owe you an apology.

I've poo poo'd your comments about Rocna's popping up all over the place for years as I haven't see that. But this afternoon I went to see the new Spades as Fisheries Supply is listed as a dealer. No Spades. Not even any old Spades and the guy hadn't heard of the new Spades. Rocna's all over the place. Lots of big SS ones w flukes about 3/4" thick. 175lbs or so. I said oh well but it looks like you're well set up to sell me a Rocna. He said yes he sells more Rocna's than anything else.

So you were/are right. Lots being sold. Didn't ask him what size he was predominantly selling. But the place looks less like Fisheries Supply and more like a Rocna store.

 

[Marin]

Eric---

Regardess of what one may think of Peter Smith as a person, he (or somebody at Rocna) did a very smart thing a number of years ago when they began having Suncoast Marine in Vancouver manufacture Rocna anchors along with the original fabrication facilities in New Zealand.

In fact when I first talked to Rocna in New Zealand to learn more about their anchor, they were the ones who told me that Suncoast had just started manufacturing them, and that it would make more sense for me to get one from them instead of from Rocna in NZ because of the huge shipping cost to send a 44-pound anchor across the Pacific. They also told me that some of Suncoast's manufacturing processes were more advanced than their own down in NZ.

In those days, Suncoast would only make a Rocna to order. They did not make them on spec. So we talked to the owner of Suncoast and ordered up a Rocna 20. They made one for us and when it was ready we drove up to Vancouver and picked it up.

The advantage to Rocna was they now had a toehold in the North American market. I may have events in the wrong order here, but Suncoast subsequently began making and supplying anchors to West Marine. Somewhere in here the company called Holdfast got involved, and to make the Rocna's price more competitive they moved all production to China. So as far as I know, at that point Rocna fabrication ceased in both NZ and Vancouver.

Then came the materials screw-up with the Chinese fabricator and Smith's, and perhaps even more so his son's, ill-conceived efforts to cover it up, which in the end really tainted the ancor's and the company's image and brand. Finally, the Rocna manufacturing rights were taken over by Canadian Metals.

But the point is that quite awhile back, Rocna established a North American presence, and despite the rocky road that ensued for awhile, that presence continues, and continues to grow.

West Marine has been carrying them for a long time now. I did not know that Fisheries Supply has also jumped on the bandwagon, as I've never wandered into their anchor section when we've visited the store.

Where I first noticed an increasing number of them was in the big Seaview North yard in our marina. They get a lot of boats from outside the Bellingham area, and once they acquired their 175 ton Travelift, they began hauling some real monsters, purse seiners and yachts and stuff. And more and more, I began seeing Rocnas on these things. Not the purse seiners, but the yachts and smaller recreational boats, power and sail.

So good move on Rocna's part all those years ago, to get a North American presence going pretty early on.

 

[Nomad Willy]

Marin,
You wrote ", to get a North American presence going pretty early on." ..... Early on would have been about 1910. But the've been making anchors for hundreds of years. Anchors didn't start w Rocna.

Got to admit those Rocna's sure looked good. Great big SS pieces of art. But I like variety and Fisheries lacked that to be sure.

As to marketing Rocna has done well. I'd rather have a Supreme even though the Rocna's look better. I'll see how my mod goes on my small Supreme and then perhaps replace my Claw w a bigger Supreme. I bought the first Supreme w that in mind.

I've got other things to worry about now ...... like getting my engine to start. May still be air in the lines .. still. Took the whole system apart and changed numerous things. Better have the engine running when we get to the slings.

 

[Marin]

Marin,
You wrote ", to get a North American presence going pretty early on." ..... Early on would have been about 1910.

Early on for the new gen anchors from Australia-New Zealand.

 

[Anchor Brian]

Below are links to the stories that have been written and posted so far about the Chesapeake Bay anchor testing. More will follow from PassageMaker, Sail, and Soundings magazines:

All at Sea:
Best Anchor for the Chesapeake Bay? - ALL AT SEA

Boat US:
The Fine Art Of Anchoring - Seaworthy Magazine - BoatUS

boats.com
Fortress Anchor Testing: When It’s Good To Be a Stick in the Mud | boats.com Blog


Unfortunately, the only writers still aboard the final day were from Sail magazine, and I think one of the most surprising moments of the testing occurred when the 10 lb (4.5) kg Fortress FX-16 was pulled a few times. Fortunately this was caught on video, and I posted a link previously.

I mention this because it adds to the discussion about whether "bigger is better." The FX-16 when set at the 45° angle had comparable holding capacity to our 21 lb (10 kg) FX-37 when it was set at the 32° angle, and so "bigger was not better".......and outside of the Danforth, the FX-16 out-performed all of the other anchors that had a huge weight / size advantage as well.

So how is that even possible? Bob Taylor, who has spent 45+ years in anchor design and soil mechanics, much of which while he was in the US Navy, answered with the below when I asked him that question:


"Bigger is not always better, it has a whole lot to do with anchor configuration. A big anchor can be very unstable (Vryhof anchors have stability problems). An anchor with the center of area/pressure on the fluke that is very close to the shank to fluke connection can be very unstable. An anchor configured such that the fluke orients itself close the direction of pull such as the cast Bruce and copycats and a number of Stevin types do not take full advantage of the large fluke area available.

Increasing palm size helps to increase the fluke bearing area by causing the fluke to rotate down during pulls in mud. It is really all about configuration.

Thinner shanks help mostly in hard soil but you have to be careful that you don’t wind up destroying the anchor on its first off line pull.

Bob Ogg/Danforth and Dick Towne/STATO and the British Admiralty did some great work many years ago to understand the influences of seemingly minor changes in anchor configuration to anchor capacity. I studied all their work with huge interest because I wasn’t interested in reinventing the wheel.

As I mentioned awhile back I took a Bruce model anchor being tested in mud at Bruce’s facility in Scotland and more than doubled its capacity by a simple addition of a sheet metal plate to the back of the anchor fluke. All it did was cause the fluke to rotate down a little."

 

[Nomad Willy]

Marin in 1975 the "new generation" anchor was the Bruce. Everybody was raving about this amazing new anchor. They appeared on the bows of boats like magic. Soon almost everybody had a Bruce except a few that stuck to their Danforths. And the Waggoner cruising guide guy recommended skippers get one before heading to Alaska. It held oil derricks before and could easily hold one's boat. And it was good on all bottoms. How could one go wrong?

Yup there's been many generations of anchors. There's nothing new about new anchors ........... except they are new now. And then they are not. The Danforth and the Claw have been mainstream for 60 and 40 years. Being 74 now I'll not see if the "new gen" of anchors achieve a legacy like that.

 

[Nomad Willy]

Brian wrote;
"As I mentioned awhile back I took a Bruce model anchor being tested in mud at Bruce’s facility in Scotland and more than doubled its capacity by a simple addition of a sheet metal plate to the back of the anchor fluke. All it did was cause the fluke to rotate down a little."

Before my recent mod that I have in mind this is what I had in mind doing as I felt the Claw lacked fluke surface area. And down is always good. But I threw it out in favor of a more roll bar like addition in the interest of insuring that all three flukes buried and the anchor seldom if ever would lay on it's side acting like a plow. And I also thought it may pitch the anchor up. This could be happening w the up elevator trailing edge of the Rocna.

 

[Nomad Willy]

Brian,
The mag articles were interesting in that given the same input such different opinions and text resulted.

By far IMO the first article was most overwhelmingly meaningful. And thus far I hadn't picked up on this part ... "After great debate and careful consideration to all anchors in the test, Hawley agreed to a change in the protocol in round five. The anchors were launched with an initial scope of 2:1 then pulled in 20 feet at 30 feet per minute until a load of 200-300 lbs. of torque indicated the anchor was set. From there the 8:1 scope was let out and the test resumed as normal. First up was the Fortress FX-37 at 45 degrees."

This seems really strange to me.

Firstly the most commonly held philosophy of setting anchors, even embraced by P Smith is to let out long scope and set the anchor. Then shorten up for swing and other considerations.

Secondly anchors aren't supposed to hold or set at 2-1 scope and many anchors being dragged at 2-1 would pull up their shank and hence their fluke tip and just drag along w hardly any resistance at all. How many anchors did'nt set in the above described manner .. and/or how many did? And what percentage of all the tests were done in this manner?

It seems very unscientific to make big changes in important steps of a scientific protocol in mid stream. One would think starting all over would be necessary to call it scientific or objective.

As to the breakouts like what happened w the Supreme could that be related to the roll bar clogging issue or theory?

Thanks for continuing to offer support for this thread.

 

[Anchor Brian]

Brian,
The mag articles were interesting in that given the same input such different opinions and text resulted.

By far IMO the first article was most overwhelmingly meaningful. And thus far I hadn't picked up on this part ... "After great debate and careful consideration to all anchors in the test, Hawley agreed to a change in the protocol in round five. The anchors were launched with an initial scope of 2:1 then pulled in 20 feet at 30 feet per minute until a load of 200-300 lbs. of torque indicated the anchor was set. From there the 8:1 scope was let out and the test resumed as normal. First up was the Fortress FX-37 at 45 degrees."

This seems really strange to me.

Firstly the most commonly held philosophy of setting anchors, even embraced by P Smith is to let out long scope and set the anchor. Then shorten up for swing and other considerations.

Secondly anchors aren't supposed to hold or set at 2-1 scope and many anchors being dragged at 2-1 would pull up their shank and hence their fluke tip and just drag along w hardly any resistance at all. How many anchors did'nt set in the above described manner .. and/or how many did? And what percentage of all the tests were done in this manner?

It seems very unscientific to make big changes in important steps of a scientific protocol in mid stream. One would think starting all over would be necessary to call it scientific or objective.

As to the breakouts like what happened w the Supreme could that be related to the roll bar clogging issue or theory?

Thanks for continuing to offer support for this thread.

Eric, thanks for your input. After every anchor had been tested 4x (48x in total - 10 competitive anchors + FX-37 tested @ both 32° & 45°) and near the end of the third day, we decided to follow and actually try our own advice in soft mud by setting not just the Fortress, but all anchors, using a shorter initial scope.

Since many of the anchors had setting issues during the course of the previous 48 pulls, we thought that we might learn something which we could then pass along to owners of these other anchors.

For example, a shorter scope with Rocna might have kept the shank more vertical and allow the fluke to dig in first and orient in the downward position.....but it didn't, nor did the shorter initial scope appear to help the other competitive anchors.

There were a total of 12 attempts with the initial shorter scope, one for each anchor, and it took us through until the end of the final day 4.


Regarding the clogging question and the Supreme, during the two pulls where it developed its highest tension, the Supreme broke free shortly afterwards and then it did not re-engage the bottom, but we saw the same thing occur with the non-roll bar Ultra, so I cannot conclude that the roll bar was to blame.

 

[Nomad Willy]

Brian.
"roll bar was to blame" ... as in caused clogging that prevented resetting?

 

[Anchor Brian]

Brian.
"roll bar was to blame" ... as in caused clogging that prevented resetting?

A couple of thoughts / observations:

- The bottom was soft gooey mud, and it is debatable as to whether many of the anchors penetrated deep enough to reach the oyster shells and firmer granular soil below.

So with or without a roll bar, the soft mud could have slide right through the anchor as it was being slowly pulled along.

- During the rare few pulls where higher tensions were achieved, and assuming that those anchors did bury deep enough to reach the firmer soil below to develop this tension, then it is certainly possible that this firmer soil compacted against the fluke, and more so with the roll bar models, as the anchor continued to be slowly pulled forward.

- So it is not difficult to theorize that the roll bar anchor would likely have a harder time shedding this compacted soil than a non-roll bar model in the event that one broke free from the bottom.

- All of that said, we did not see EITHER anchor-type re-engage the bottom after breaking free....and they typically came up relatively clean as well.

Obviously, it would have been ideal to have had underwater cameras to film all of this, but the water was far too murky to consider this possibility.

Brian

 

[Djbangi]

Eric,

You comment on the disparity of views of the 3 articles printed.

It is obvious from any anchor thread that everyone has their own ideas on anchors and have their own favourites. We all have preconceived ideas and some people are not too happy having those pre-conveived ideas contradicted. Authors are human. Even in the short time I have been here I note some acceptance of views now that were not accepted a few weeks ago - so members on this thread are willing to think more deeply and consider that what they believed in might need some tweaking. Members here also see through the spin and soon see through any bias and detect the smoke and mirrors of the snake oil salesman.

The media has few anchor experts, most boating magazines have staff who generalise, you cannot expect them to know all the detail of electronics, cordage, engines, boat handling, hull design, sails etc. You cannot expect them to know about anchor testing. I suspect many who contribute to this thread have a better idea on anchors than many, or most boating writers.

But the power of having the media on board was to ensure the tests were 'fair' and there seems to have been a decent cross section to ensure that Fortress had not manipulated the tests to their advantage. But to me one of the results was a foregone conclusion, otherwise we would not have seen the results. I found the testing of the other anchors, for which Fortress has no interest on relative merits whatsoever, more interesting. I do not believe a 10% or 20% difference in performance too meaningful (variations in seabed can easily cause that, and I do not think a user can detect that advantage anyway) - but factorial differences jump out and should hit you in the face.

I do not believe we have seen all the data yet, or there could be some interesting data hidden in the background. Fortress did much the same sort of thing, same sort of seabed, in the early 90's (and might have done something in sand). Obviously they did not test many of the modern anchors but it would be useful to see how consistent the test protocols are and how the Fortress (Danforth, CQR etc) performed then as to now. It might also be interesting to put up any sand results alongside those of today.

The other aspect I note is that the Fortress protocol demanded pulling the anchors, whatever the result, over a long distance. In reality if it was us we would discard the pulling, if no set was developing, pretty sharply. Consequently the averages should be based on discarding those pulls that did not work (but emphasising how many pulls make up the average). Obviously some anchors never set, so developing an average is difficult.

I do think our analysis of the results might be better than some of the media.

The testing appears to have been scrupulously fair, it turned over some stones showing some nasties hiding underneath and for Fortress it produced a result to (hopefully) justify the costs. I'd like to see the same tests in sand - but the costs of this one test must have been huge. Fortunately this is the sort of test that will be quoted for decades. Excellent legacy testing.

Jonathan

 

[Anchor Brian]

Jonathan,

Thanks for your input. What has not been released yet by Fortress are reports with interpretations of the data. We hired Bob Taylor and Chuck Hawley to write two separate reports on the testing, with Bob's views coming from one who has a very scientific perspective, and Chuck's views are from one who was an eyewitness aboard the test vessel, and from a boater with an extensive background in testing boating products.

As you might expect, their analysis of the data and their reports are intelligent and insightful, and yet in some cases, quite different, which has led to lengthy discussions and delays in releasing the final reports.

There was one writer aboard who is also writing a book on anchoring, and his magazine story is sure to be hard-hitting. He and his wife are liveaboards and he spent all 4 days on the Rachel Carson. His analysis and opinions were often critical and detailed, which we fully welcomed.

This writer was particularly critical of anchor manufacturers who make model recommendations without any supporting back up information regarding the holding power capabilities of their anchors in common bottom conditions. This testing in soft mud only magnified his concerns, as there were many anchors which would not hold boats for which they are recommended in anything other than very light winds, if at all.

He also felt that we at Fortress needed to do a better job ourselves in corresponding the ABYC horizontal loads table into model recommendations as well, to which I fully agree.

Regarding further tests in sand, the initial plan was to follow what we did in 1990 with soft mud testing in SF Bay (the Chesapeake Bay was chosen for this) and sand testing locally in Miami, and again, include all of the "old generation" models from those tests and the "new generation" models.

I will keep you posted on any progress with our sand bottom test plans.

Brian

 

[Delfin]

Below are links to the stories that have been written and posted so far about the Chesapeake Bay anchor testing. More will follow from PassageMaker, Sail, and Soundings magazines:

All at Sea:
Best Anchor for the Chesapeake Bay? - ALL AT SEA

Boat US:
The Fine Art Of Anchoring - Seaworthy Magazine - BoatUS

boats.com
Fortress Anchor Testing: When It’s Good To Be a Stick in the Mud | boats.com Blog


Unfortunately, the only writers still aboard the final day were from Sail magazine, and I think one of the most surprising moments of the testing occurred when the 10 lb (4.5) kg Fortress FX-16 was pulled a few times. Fortunately this was caught on video, and I posted a link previously.

I mention this because it adds to the discussion about whether "bigger is better." The FX-16 when set at the 45° angle had comparable holding capacity to our 21 lb (10 kg) FX-37 when it was set at the 32° angle, and so "bigger was not better".......and outside of the Danforth, the FX-16 out-performed all of the other anchors that had a huge weight / size advantage as well.

So how is that even possible? Bob Taylor, who has spent 45+ years in anchor design and soil mechanics, much of which while he was in the US Navy, answered with the below when I asked him that question:


"Bigger is not always better, it has a whole lot to do with anchor configuration. A big anchor can be very unstable (Vryhof anchors have stability problems). An anchor with the center of area/pressure on the fluke that is very close to the shank to fluke connection can be very unstable. An anchor configured such that the fluke orients itself close the direction of pull such as the cast Bruce and copycats and a number of Stevin types do not take full advantage of the large fluke area available.

Increasing palm size helps to increase the fluke bearing area by causing the fluke to rotate down during pulls in mud. It is really all about configuration.

Thinner shanks help mostly in hard soil but you have to be careful that you don’t wind up destroying the anchor on its first off line pull.

Bob Ogg/Danforth and Dick Towne/STATO and the British Admiralty did some great work many years ago to understand the influences of seemingly minor changes in anchor configuration to anchor capacity. I studied all their work with huge interest because I wasn’t interested in reinventing the wheel.

As I mentioned awhile back I took a Bruce model anchor being tested in mud at Bruce’s facility in Scotland and more than doubled its capacity by a simple addition of a sheet metal plate to the back of the anchor fluke. All it did was cause the fluke to rotate down a little."

Brian, I never really thought of the 'bigger is better' argument as meaning that a heavier CQR is superior to a lighter Fortress. As I take it, the heavier of two identical anchors will always provide superior holding to its lighter twin. For that not to happen, I think the laws of physics would need suspending. I don't think the comparison of the FX 16 at 45 degrees holding better than an FX 37 at 32 degrees demonstrates anything different, unless you feel that the 37 set at 45 degrees would still be outpulled by the 16. Don't think that would occur.

 

[Anchor Brian]

As I take it, the heavier of two identical anchors will always provide superior holding to its lighter twin.

Delfin,

Agreed. In fact, Bob graphed all of the data from the SF and Chesapeake Bay tests, and as the Fortress anchor physical sizes / weights increased, so did the capacities with comparable holding ratios (holding capacity / anchor weight).

The point that I was hoping to make was that a very small and light anchor (FX-16), when configured properly for the bottom condition (wider shank/fluke angle for soft mud) would perform far better than a much larger anchor, even of the same design, which was not configured properly.

So in that example, bigger is not better.

Brian

 

[Delfin]

Delfin,

Agreed. In fact, Bob graphed all of the data from the SF and Chesapeake Bay tests, and as the Fortress anchor physical sizes / weights increased, so did the capacities with comparable holding ratios (holding capacity / anchor weight).

The point that I was hoping to make was that a very small and light anchor (FX-16), when configured properly for the bottom condition (wider shank/fluke angle for soft mud) would perform far better than a much larger anchor, even of the same design, which was not configured properly.

So in that example, bigger is not better.

Brian

Again, bigger is better doesn't apply to unlike entities. As Fortress has shown, a light weight anchor properly designed can be superior to a heavier anchor of a different design. However, the heavier Fortress will have higher holding capacity than the identical lighter Fortress - in other words, bigger is better.

 

[Djbangi]

Delfin and Brian,

I think you are saying both something similar but in line with anchor thread policies want to pretend to disagree

My point is Bigger Might be Better but is unnecessary, unless you have a social conscience and want to allow anchor makers early retirement!

But Brian, thank you for the post indicating there are further analysis and data to be released. I will look forward to reading it/them. The published articles to date have been a bit brief and even more bland. It is also good news that you intend to update your data on the use of the Fortress is sand, in comparison to the current batch of anchors, - hopefully sales will increase for you from this recent batch of testing to fund the exercise (or you will be retiring late).

Jonathan

 

[Peter B]

Delf et al, I think the point here surely is that the anchor that is deeply set, gives better holding, than one barely set, basically just sitting on the bottom. So you could, at least theoretically, have a smaller yet identical design perform better, and in fact Brian's case of the F16 outperforming a 35, due to being more deeply set, is an actual example, so more than theoretical in this case, albeit because it's throat angle was wider and therefore better for a soft bottom.

I guess therefore, an extreme example of bigger not being better is two identical designs, but one so big the boat it was anchoring could not exert a force large enough to bury it, (admittedly an extreme and unlikely scenario), whereas the smaller one was buried deeply because it was smaller. That would then give greater holding than a larger one, sitting almost on the surface of the seabed, as it could be more easily dragged along, if things suddenly got nasty before the bigger anchor could dig in. As I said, an unlikely event, but theoretically possible I suppose. Beware the throat angle, I guess.

 

[Djbangi]

I'm not sure that Bigger is Better is such an issue for Trawlers. The original debate was initiated on a sail cruising forum where motors are meant to be auxiliary power units (and consequently small). Trawlers rely on their engines, exclusively, and their engines tend to be much larger.

As a rule of thumb it has been suggested that for every 10hp you might develop 100kg of power/load - but this is in forward gear (props are less efficient in reverse) and this simplistic formula might not be applicable for larger (and slower rpm) engines - and maybe the props are more efficient. The formula does not work either for outboards, which cavitate quickly.

But on the basis that Trawlers (and many motor boats) have a greater (or larger) power ratio, vs either length or displacement, compared to a yacht then a Trawler should be able to set an anchor, more deeply, than that same anchor by a similar length yacht.

Though none of this explains why many power boats have minimalist anchors.

But Delfin has a comparatively large anchor and I suspect large reserves of power - and is able to set that anchor deeply, under power alone. Give him a 50 or 60 hp engine - and he would struggle (to set it deeply). Consequently Delfin can set that anchor properly, there should be no issue of it pulling out (in a wind shift) because poorly set and then having to re-set itself. Now if Delfin were to become paranoid and feel the need for a 200kg Ultra (and also feel the need to lighten his wallet) then the discussion comes back into play. Yes it might be better (or not) but does he need it, the bigger anchor (he might still feel that social need to increase the anchor maker's pension fund).

And coming full circle - a smaller anchor (of the right design) in a hard seabed might develop better holding than a larger one (that had difficulty in penetrating that harder seabed).

Its horses for courses.

Jonathan

 

[ranger58sb]

Though none of this explains why many power boats have minimalist anchors.

Only some relatively minor percentage of powerboaters around here actually anchor out, and even those that do don't necessarily anchor out very often... and might not even notice if they have a useful anchor (or if it held) or not. (Fling it overboard, open a beer...)

Marina hopping is more the norm, in this area.

I think that means makers can slap a small Delta (or whatever) on the nose of just about any power boat, call it victory... and the buyers and subsequent owners seldom notice.

And then Deltas (or others) generally work pretty well anyway. Maybe not the latest and greatest, maybe not perfect in all substrate, but "generally" is often good enough.

-Chris

 

[sunchaser]

I'd guess 99%+ of those that anchor do so in sheltered waters. For the 1%ers once an anchor type has been selected it is quite common to go a size or two up (or much more in some cases) to insure no dragging on lower scopes.

Ditto more muscle for the ground tackle which has had little mention in this anchor discussion - say all chain vs short chain connected to rope on a pull test.

 

[Delfin]

I'm not sure that Bigger is Better is such an issue for Trawlers. The original debate was initiated on a sail cruising forum where motors are meant to be auxiliary power units (and consequently small). Trawlers rely on their engines, exclusively, and their engines tend to be much larger.

As a rule of thumb it has been suggested that for every 10hp you might develop 100kg of power/load - but this is in forward gear (props are less efficient in reverse) and this simplistic formula might not be applicable for larger (and slower rpm) engines - and maybe the props are more efficient. The formula does not work either for outboards, which cavitate quickly.

But on the basis that Trawlers (and many motor boats) have a greater (or larger) power ratio, vs either length or displacement, compared to a yacht then a Trawler should be able to set an anchor, more deeply, than that same anchor by a similar length yacht.

Though none of this explains why many power boats have minimalist anchors.

But Delfin has a comparatively large anchor and I suspect large reserves of power - and is able to set that anchor deeply, under power alone. Give him a 50 or 60 hp engine - and he would struggle (to set it deeply). Consequently Delfin can set that anchor properly, there should be no issue of it pulling out (in a wind shift) because poorly set and then having to re-set itself. Now if Delfin were to become paranoid and feel the need for a 200kg Ultra (and also feel the need to lighten his wallet) then the discussion comes back into play. Yes it might be better (or not) but does he need it, the bigger anchor (he might still feel that social need to increase the anchor maker's pension fund).

And coming full circle - a smaller anchor (of the right design) in a hard seabed might develop better holding than a larger one (that had difficulty in penetrating that harder seabed).

Its horses for courses.

Jonathan

Jonathan, we're still not on the same page. Given the choice between a 20# Fortress and a 50# CQR, I would choose the Fortress. But that is not what the argument for BiB is about. Given the choice between a 40# CQR and a 50# CQR, I would choose the bigger CQR because its holding and penetrating capacity would be greater. Its holding capacity is greater because of gravity and its penetrating capacity would be greater because its mass is greater per square inch of surface area that has to penetrate. That is BiB.

A heavier Fortress set up the same as a lighter Fortress will also have greater holding/penetrating power for the same reason. That is BiB. Comparing one Fortress without mud flaps to another with tells us nothing about BiB because you are comparing unlike entities. But is is simply physics and geometry that dictate that BiB is ALWAYS the case when comparing the same anchors. This is so geometrically because as you increase the mass of an object, its surface area will not go up proportionately to the increase in its mass, meaning that as anchors get heavier their penetration capacity goes up regardless of the sea bed because more mass is concentrated per unit of surface area. This is so by the laws of physics because gravity works under water as well and the effect of gravity is a function of mass.

Delfin's anchor is one size larger than needed. It therefore has greater holding and penetrating capacity than an Ultra one size smaller. Would I be held better with a 1,000# Ultra? Of course, because BiB is ALWAYS the case but it is not feasible since I couldn't carry a 1,000# anchor, which is why the sensible advice is choose an anchor, then carry the biggest one that fits your budget, windlass, chain and boat.

Whatever your horsepower, whatever the size of boat, whatever your anchoring technique, Bigger is always Better and always will be until they suspend the laws of physics.

 

[Nomad Willy]

Peter wrote;
"I guess therefore, an extreme example of bigger not being better is two identical designs, but one so big the boat it was anchoring could not exert a force large enough to bury it, (admittedly an extreme and unlikely scenario), whereas the smaller one was buried deeply because it was smaller. That would then give greater holding than a larger one, sitting almost on the surface of the seabed, as it could be more easily dragged along, if things suddenly got nasty before the bigger anchor could dig in. As I said, an unlikely event, but theoretically possible I suppose. Beware the throat angle, I guess."

If the boat couldn't exert enough force to bury the large anchor but could bury a much smaller one when the wind picked up sufficiently the bigger anchor would hold the boat or penetrate the seabed, bury and hence hold the boat. With the same bottom and exactly the same anchor (except size) both should set and bury. But if even more wind came along the the big anchor should bury deeper and at some point (wind wise) the smaller anchor should break out and most importantly (for this discussion) the bigger anchor would stay buried until the wind got even stronger and then it would break out also. Bigger is better.

Brian's anchor performed better because it was NOT the same. It had a wider fluke angle.

 

[Djbangi]

Delfin,

I have to differ.

For one gravity has nothing, or an insignificant effect, to the holding of an anchor. The anchor develops hold because it is loaded and driven into the seabed. That load can be either an engine(s) or wind. Gravity will have an effect, but most of us to do not have the time to wait for an anchor to settle (mooring concrete blocks are an example, over a year they settle).

Theory suggests an anchor with a larger surface area will have a higher holding capacity than a smaller one, assuming the same design and the same seabed. The same seabed means the same depth, as seabed has a higher shear stress with depth. However to develop that higher hold a higher setting load must be applied.

But to realise the potential of that higher surface area means that the bigger anchor must be driven down sufficiently.

The developed holding capacity of an anchor is defined by the load, if you load an anchor with 200kg then that, effectively, will be its holding capacity, whether its a big or a small anchor. It will not be bigger because its a bigger anchor - the capacity is all dependent on the load.

The only case where bigger is better is when you exceed the maximum holding capacity of the small anchor in that seabed. Once an anchor reaches its limit it will then swim horizontally, inevitably meet a contaminant and then surface and drag. As long as the small one is large enough for whatever conditions are thrown at it then its capacity will always be within its limits and a larger anchor (of the same design) will not develop a higher hold - it cannot set at a higher load as the load is the same (imposed by the same vessel). The larger anchor will be higher in the seabed (it can develop that hold at a shallower depth).

Bigger is better is only relevant if the small anchor is too small.

Its then a discussion on 'what is too small', not 'what is too big'

Jonathan

edit: There is evidence to support the above. Those who take images of their anchors, that are excessively large, )without exception) show anchors with part of the anchor still protruding above the seabed. This suggests that whatever load was imposed on them, engine or wind, was insufficient to have them dive completely. To me a well set anchor is one you cannot see. The big anchor has potential - but if its too big then that potential will never be realised - and you are just filling that pension fund (instead of enjoying malt whisky yourself - each to their own)

end edit

 

[Delfin]

Delfin,

I have to differ.

For one gravity has nothing, or an insignificant effect, to the holding of an anchor. The anchor develops hold because it is loaded and driven into the seabed. That load can be either an engine(s) or wind. Gravity will have an effect, but most of us to do not have the time to wait for an anchor to settle (mooring concrete blocks are an example, over a year they settle).

Theory suggests an anchor with a larger surface area will have a higher holding capacity than a smaller one, assuming the same design and the same seabed. The same seabed means the same depth, as seabed has a higher shear stress with depth. However to develop that higher hold a higher setting load must be applied.

But to realise the potential of that higher surface area means that the bigger anchor must be driven down sufficiently.

The developed holding capacity of an anchor is defined by the load, if you load an anchor with 200kg then that, effectively, will be its holding capacity, whether its a big or a small anchor. It will not be bigger because its a bigger anchor - the capacity is all dependent on the load.

The only case where bigger is better is when you exceed the maximum holding capacity of the small anchor in that seabed. Once an anchor reaches its limit it will then swim horizontally, inevitably meet a contaminant and then surface and drag. As long as the small one is large enough for whatever conditions are thrown at it then its capacity will always be within its limits and a larger anchor (of the same design) will not develop a higher hold - it cannot set at a higher load as the load is the same (imposed by the same vessel). The larger anchor will be higher in the seabed (it can develop that hold at a shallower depth).

Bigger is better is only relevant if the small anchor is too small.

Its then a discussion on 'what is too small', not 'what is too big'

Jonathan

edit: There is evidence to support the above. Those who take images of their anchors, that are excessively large, )without exception) show anchors with part of the anchor still protruding above the seabed. This suggests that whatever load was imposed on them, engine or wind, was insufficient to have them dive completely. To me a well set anchor is one you cannot see. The big anchor has potential - but if its too big then that potential will never be realised - and you are just filling that pension fund (instead of enjoying malt whisky yourself - each to their own)

end edit

Sorry Jonathan, but that is simply contrary to the laws of physics. To say that gravity has little effect on a heavier anchor setting, that has with greater mass per square inch of surface area than a lighter anchor of the same design simply cannot be affirmed by reality. If gravity had no effect, then there would be no reason not to make all anchors small. Does the below anchor look small? Why do you think that to anchor an oil rig they use a really big anchor if size and gravity has no effect?

The effect of gravity is exactly the same in water as it is on land. I know this seems counter intuitive, but it is true. Is the force of gravity greater less or equal in water than on land.

A heavier anchor, e.g. 'bigger', will always have greater setting capability than a lighter anchor of the same design and configuration. This isn't me talking. It's Isaac Newton.

 

[Djbangi]

I'll take an example of the 'problem', from Fortress Chesapeake mud tests.

The 45lb Mantus had an average hold of about 680lb which is enough to hold a 30' vessel in 30 knots of wind. A 40' vessel (a vessel size close to the size rated for the 45lb Mantus for cruising), in 30 knots of wind, would need a Mantus of around twice the size, so 90lbs, in order to develop the required hold of 1,200lbs - noting that none of this offers any safety margin (and I'm making the assumption, possibly erroneous, that doubling size, doubles hold). (Hold or load data from ABYC.)

You decide on a safety margin, a minimalist factor of 2 brings in a rather large 180lb Mantus.

The Bigger is Better thesis was that carrying a bigger anchor, because it was 'so safe', offered the opportunity to only need one anchor. The enough is enough thesis was that you do not need that ridiculously large anchor but a suite of small anchors, so instead of the 90lb or 180lb Mantus you have a recommended sized Mantus, say 45lb and a Fortress FX-37, 21lb and which will give you a rather 'comfortable' hold of average about 1,900lbs (or a Danforth a size or couple of sizes up from the 35lb model tested).

It does not matter what sized anchor you have, you might lose it, damage, irretrievably stuck. Carring a spare 90lb anchor, looks a bit inconvenient, a second 45lb anchor (in addition to the Fortress) looks very attractive (unless you have a crane on the bow).

Again, I paint black and white - shades of grey would be better.

Jonathan

 

[Djbangi]

Delfin,

If you take an anchor and sit it on the seabed it is already affected by gravity - it does not set!

Gravity does not vary - its the same gravity whether its sitting there smiling at you or scowling because you pull it. Once it gets over its scowl it sets because of design and the fact you pull it (the gravitational effect does not increase because you pull it).

Oil rigs use bigger anchors because they develop more hold.

A Danforth heavier than a Fortress develops the same hold (at 32 degrees) even though the Danforth is 50% heavier. A 15kg steel Excel of exactly the same design and dimensions to the nearest mm, or thou, develops the same hold as a 9kg alloy model. A 15kg Steel Spade develops exactly the same hold as a 9kg alloy model of the same dimensions. I've tested the Spade and Excel and I think you will find that Anchor Right will confirm something similar for their Excels.

Jonathan

edit: Finally - there are a huge number of University research papers (Houston is a base of excellence) on anchor design. In terms of hold - weight it totally irrelevant, its all about surface area (for a given design). The problem is that as the anchor gets bigger (in area) it needs to be stronger and the only way to make it stronger is to use thicker steel and thicker steel is heavier.

You can save weight by using stronger steels - but there is a limit to the steels you can use and then the equation becomes the same, to be strong enough it must use thicker steel, its then heavier.

If you still do not believe I'll try to find a dissertation examining this very feature (its a bit heavy, I think 500 pages long - but then it is about anchors)

close edit

Jonathan

 

[markpierce]

So what's the principle, if not gravity, behind semi-permanent anchors such as the mushroom-type on this lightship?

 

[HopCar]

"You can save weight by using stronger steels - but there is a limit to the steels you can use and then the equation becomes the same, to be strong enough it must use thicker steel, its then heavier."

I heard a rumor that Fortress was making a carbon fiber anchor that is even lighter than their aluminum anchors.
(Actually I didn't hear that rumor, I'm trying to start it.)