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Old 09-12-2014, 07:51 PM   #381
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I guess I'm lucky. Here in the Pacific our tides change four times a day, not two like the east coast. Therefore the swings are lessor and the changes milder. If I anchor in a single hook I seldom do a 360 or a 180. There isn't a pull out and reset here.

For current, which we get at the Islands double anchoring is best and sometimes tying to a rock on shore is a great option. My usual system is to drop bow and back the boat near the shore and then drop the stern off the swimstep. Then I winch the bow as I lay out the stern and everything sets. After that, reset. Then it's done.

Pulling is easy, back up and retrieve the stern then pull the bow.

A FX stern would be fine for me as nearer the shore the more mud.sand mix you get here.
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Old 09-12-2014, 07:59 PM   #382
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Verring test;
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Old 09-12-2014, 08:02 PM   #383
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I guess I'm lucky. Here in the Pacific our tides change four times a day, not two like the east coast. Therefore the swings are lessor and the changes milder. If I anchor in a single hook I seldom do a 360 or a 180. There isn't a pull out and reset here.

For current, which we get at the Islands double anchoring is best and sometimes tying to a rock on shore is a great option. My usual system is to drop bow and back the boat near the shore and then drop the stern off the swimstep. Then I winch the bow as I lay out the stern and everything sets. After that, reset. Then it's done.

Pulling is easy, back up and retrieve the stern then pull the bow.

A FX stern would be fine for me as nearer the shore the more mud.sand mix you get here.
2 high tides and 2 low tides?

I Check Santa Monica real quick and it looked like that...which would be the same as the East Coast....

Gulf Coast can have some areas of unusual tides if I remember correctly.
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Old 09-12-2014, 08:20 PM   #384
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For the Supreme or the Rocna to develop it's maximum holding power I would imagine it to be "clogged" as you say. As I've stated earlier the roll bar clogging (forcing the substrate through the "hole" between the roll bar and the fluke) probably produces a good portion of it's resistance. Resistance it is .. but far from the holding power of a good fluke. Your SARCA is far less subject to this "jam the substrate through the slot" kind of "after effect holding power" function that powers the Supreme and the Rocna to a great extent.

When I finish experimenting w my Supreme it will no longer be a roll bar anchor.
I'm just not buying the roll bar squeezing the substrate theory. The bar is not that big and I would think many/most bottom types are at least some what compactible/compressible. I just find it hard to believe it has that much, if any, effect on the anchor as it digs in. I can see how the roll bar may have some effect due to drag. But that's about it.

Does anybody have any proof of this squeezing theory and how it negatively effects hooped anchors? Or is everybody just guessing on this?
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Old 09-12-2014, 08:43 PM   #385
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Mantus themselves said their anchor set more deeply without the roll bar, omitting to mention that if it landed on its back it would never set at all. Practical Sailor found that a roll bar anchor, again a Mantus, without its roll bar would set more deeply (and deeply usually means with a higher hold).

Commonly at a change of tide the direction of the vessel, in relation to the anchor, changes slowly and the loads immediately after a tide change are low. In terms of tide and veering, most anchors have the ability to shuffle round in a tide. If the initial set is not deep, hard substrate or not power set, then the anchor might pull out - then re-setting ability is important (and an ability not to pick and clog anything in the fluke as this will retard or totally stop resetting)

Arguably a well set Fortress would simply not move in a change of tide (based on the difficulties described in the Chesapeake trials in lifting the Fortress - though these were based on setting very deep to start with and a lightly set Fortress might 're-set' differently to a well set Fortress).

The big issue is the 'worst case scenario' (not the change of tide) when there is a sudden change of loading direction - the best example (but not only) is if a severe tropical thunderstorm passes directly overhead and wind directions change from 40 knots in one direction to 40 knots in the opposite direction (with nothing in between). This can also occur in a tidal river when an anchor is set in one direction but a severe frontal system moves through loading the anchor in the opposite direction to the tidal set.

Some of this emphasis the importance of power setting, getting the anchor as deep as possible.

This is a situation where anchor strength, or integrity, comes into play as anchors are not necessarily designed to take loads that are not along the length of the shank - and a well set modern anchor suddenly loaded at an angle to the shank (where the fluke is effectively immobile - it has high holding) might result in the shank bending. Proof Testing is one way of reassuring the customer (Ultra, Anchor Right (both Super SARCA and Excel), Fortress, Delta, Supreme etc - but there are some notable omissions). Though most anchors seem to bend on retrieval.

One might argue that these are extreme cases - but many have experienced the situation so they are not that unusual.
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Old 09-12-2014, 08:44 PM   #386
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Something not being mentioned is the liquefaction of soils when under water and agitated. Not sure if it is true soil liquefaction but, let's go with the flow in that direction of totally saturated soil.

Many discussions of anchors forget this issue and some anchor tests have actually been done oout of the water.

While discussing "digging in" and "holding" and a "lot" of things..just like tests done out of the water only show a small portion of "reality" as opposed to "theory" and not very good ones at that.

Ever see how fast a plié is driven into even a hard bottom when enough water jet is applied? Because of saturated and muddy soil is exactly why a mushroom anchor was favored for so long. As it wobbled around...it settled deeper and deeper, even with very little pull applied.

So an anchor that's allowed to wiggle and settle can do all sorts of things other than "compress soil" or anything else for that matter.
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Old 09-12-2014, 09:18 PM   #387
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Something not being mentioned is the liquefaction of soils when under water and agitated.
Moreover, thixotropic clays which would favour a flat planar surface such as a Danforth or Fortress...
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Old 09-12-2014, 09:27 PM   #388
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We use a mushroom anchor for our swing mooring, except that our mushroom anchor is a simply 0.5t of concrete (with a steel rod up the centre). It settles into the seabed and on lifting for its annual service, primarily the chain and swivel, has sand on top, suggesting it settles well - but this is over 12 months. Many mushroom anchors, lightships, nav buoys, I know of were used the same way - over months, not hours.

All seabed is saturated, totally, and a minimum porosity is around 18% with normal particle grading (you can get lower with lower depths as there are greater pressures. You can get lower with fancy particle mixes - which might not occur in nature). However take a 18% porosity 'body' and it appears dry.

In the Chesapeake tests I'm guessing the top layers have much higher porosity and a lot more water, than 18% and it looks or feels more like porridge or custard than a dry 18% porosity body. But have a look at the images of the anchors retrieved after a good set in the Chesapeake tests and you will note that the flukes are packed with what looks like 'almost' dry seabed - all, or down to 18%, of the water has been squeezed out (either by the act of setting or because the anchor is so deep it is into a compressed layer with close to that minimum 18% porosity).

Liquifaction is undoubtedly a feature and I believe is the reason for the slots in the Super SARCA and Excel but the act of liquefaction will vary with depth and seabed - more at the top and less deeper, more in mud and less in hard sand.
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Old 09-12-2014, 10:09 PM   #389
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I have had go out with a tow boat on two occasions to break a fortress anchor free from a sandy/muddy bottom after a storm. I was shock I did not break the line before the anchor came free. I you use a fortress anchor don't go light on the hardware.
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Old 09-12-2014, 10:28 PM   #390
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What I do when I worry about holding. I use a tried and proven method of setting a second anchor at approx. 60 degrees. I usually set the primary presently a 60lb ultra with heavy chain and a secondary aluminum anchor with short chain and rode from my dinghy. If my worries about the conditions do materialize I let out some extra scope. I am thinking of adding a short wire to the primary anchor to allow deeper dig in. There is nothing new about this just pointing it out as a simple solution to the problem of anchoring where a single anchor of one type might not be the best solution. My primary is a type that will usually set fast in most bottom. Once my boat is anchored I have lots of time to select and deploy the secondary. This way even a hard to set anchor such as a Danforth type can be set at leisure. By the way Three Danforth type anchors set at equal angles and tied together to one rode makes the bet dame mooring anchor rig short of 5 tons of cement.
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Old 09-12-2014, 10:57 PM   #391
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Interesting... Are you saying if you anchored further out an a single hook, with enough scope to swing 360° if it were to happen, you'd be out far enough so there'd be other folks anchored there, too?

Or that you wouldn't trust any single anchor to the conditions there, since you're often gone (off the Tolly) for long periods?

Or both? Or neither? Or...?

Have to admit, I'm usually trying to be "creatively lazy" and all the work associated with a stern anchor doesn't entice.

-Chris
Chris

SF Delta smallish back-sloughs, although relatively deep, are usually quite narrow... approx. 100' to 250' +/- wide.

Soooo, being that they are occasionally used as travel canals for small cruisers and sometimes ski areas for sports people and at times quiet fishing spots for one to three persons aboard small outboards there are seldom locations where a boat can be anchored in center for full swing capability. Even larger front-sloughs are seldom more than 4 to 6 hundred feet wide; and, usually much more traveled by many types of boats; not much swing-anchor room there either. Occasionally there are junctions where sloughs meet that provide expanses large enough for swing anchor technique. Those areas are usually heavily traveled and sometimes with too many anchored boats.

If we want to “anchor” for enjoying these desirous-to-us back-slough locations it is necessary that we anchor close to shore. Dual (bow and stern) anchoring is preferred… basically necessary!

Hope that clears the picture for your mind’s eye.

Search the net and you can locate SF Bay Delta maps… as well as great history stories. Interesting, great reads. There are over 1,000 miles of rivers and sloughs. The Delta’s sloughs are basically, entirely a man-made organization of levies that formed hundreds of canals for purpose of creating our nations “bread basket” for vegetable farms whose growth products exist/thrive on Deltas’ fresh water.

To better understand I suggest net-search for maps, pictures, historic stories!


Happy SF Delta-Research Daze! - Art
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Old 09-12-2014, 11:20 PM   #392
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CaptBill11,
The interplane drag or compaction function clearly plays a role in resistance but the question is how much. In soupy non-viscous slimy mud it probably amounts to practically nothing but in hard clay like bottoms I'm convinced it has considerable effect on performance. It very neatly explains why the Rocna performs so poorly in soup compared to other anchors and so well in hard bottoms.

And I'm also convinced the roll bar tends to pitch the anchor up in it's fwd progress through the bottom. Drag applied high on the anchor will pitch the anchor up. I flew an ultralight that had a high wing and rudders at the wing tips above the wing. The rudders could be deployed simultaneously and that was the quickest way to do a whipstall .... Pitching the aircraft up very quickly. Drag high up in a vehicle does pitch it up.
Also the trailing edge of the Rocna is configured like an up elevator that (no doubt IMO also pitches the anchor up. The upturned trailing edge also creates more drag and hence more holding power. Fortunately the fluke overcomes most of that problem but the Rocna and to a great extent also the Supreme dosn't seem to penetrate below more than an inch or so under the surface. Most anchors in most bottoms probably don't penetrate much below the surface but the roll bar anchors are more limited than most ... IMO.
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Old 09-13-2014, 08:31 AM   #393
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SF Delta smallish back-sloughs, although relatively deep, are usually quite narrow... approx. 100' to 250' +/- wide.

Soooo, being that they are occasionally used as travel canals for small cruisers and sometimes ski areas for sports people and at times quiet fishing spots for one to three persons aboard small outboards there are seldom locations where a boat can be anchored in center for full swing capability.

If we want to “anchor” for enjoying these desirous-to-us back-slough locations it is necessary that we anchor close to shore. Dual (bow and stern) anchoring is preferred… basically necessary!

Ah. Got it. Thanks for 'splaining.

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Old 09-13-2014, 11:48 PM   #394
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CaptBill11,
The interplane drag or compaction function clearly plays a role in resistance but the question is how much. In soupy non-viscous slimy mud it probably amounts to practically nothing but in hard clay like bottoms I'm convinced it has considerable effect on performance. It very neatly explains why the Rocna performs so poorly in soup compared to other anchors and so well in hard bottoms.

And I'm also convinced the roll bar tends to pitch the anchor up in it's fwd progress through the bottom. Drag applied high on the anchor will pitch the anchor up. I flew an ultralight that had a high wing and rudders at the wing tips above the wing. The rudders could be deployed simultaneously and that was the quickest way to do a whipstall .... Pitching the aircraft up very quickly. Drag high up in a vehicle does pitch it up.
Also the trailing edge of the Rocna is configured like an up elevator that (no doubt IMO also pitches the anchor up. The upturned trailing edge also creates more drag and hence more holding power. Fortunately the fluke overcomes most of that problem but the Rocna and to a great extent also the Supreme dosn't seem to penetrate below more than an inch or so under the surface. Most anchors in most bottoms probably don't penetrate much below the surface but the roll bar anchors are more limited than most ... IMO.
Eric, I think you are over-thinking the up-turning drag effect of a roll bar. To bury one of these type of anchors deep enough for the roll bar to be covered requires such force, which is concentrated in the horizontal pull on the shank, I doubt any elevating effect of the bar would even register, unlike the effects of control surfaces on an aircraft where much higher speeds are involved and the medium being travelled through is way less dense than bottom mud.
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Old 09-14-2014, 12:30 AM   #395
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Most 'modern' anchors can be completely buried, by the vessel's engine or wind, in sand - roll bar or not. They can be buried such that there is no sign of the anchor and in some seabeds you can easily also bury 6' - 10' of chain, obviously including the shackle and any swivel.

In such circumstances the resistance of the chain, think of its surface area, is in effect infinite and the deeper the anchor dives the more resistance the chain produces (because more chain needs to be dragged down the deeper the anchor dives). The roll bar, though it is quite a large surface area, is finite - but once the anchor is righted - it is just drag (though it might contribute to compression).

eyschulman has the right idea, add a wire trace to the rode, between chain and anchor, and you will minimise this drag effect of the chain. Cutting out the swivel, or moving it 6' away from the anchor, would also help. Both the XYZ and HT Danforth have been supplied with a wire trace attached. There are safety issues with a wire trace - the integrity of the swages being the main one - but as long as you think of the trace as a consumable and are conscious of the problems - I cannot see any issues (only advantages). You can easily buy tested wire strops with swages. And again Practical Sailor had an article about the drag impact of chain and wire. Wire rodes are quite accepted on vessels 'in survey' its not a new idea (though a complete wire rode might be chosen for factors other than the aid it might give to the anchor setting).

If you are lucky to anchor in clear water over sand (not hard sand) you can see this effect quite easily as the chain 'disappears' into the seabed and there can be no sign of the anchor.

But why - in the Fortress Chesapeake mud trials - the Mantus did less badly, compared to the Supreme and why the Rocna was such a, consistent, disaster - given that previously one might have said they were 'similar' - remains something of a mystery. In the same way that the Ultra outshone the Spade. The more we learn about anchors, the bigger the differences between them and the less we seem to know!
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Old 09-14-2014, 11:39 AM   #396
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Djbangi,
Interesting comment about the Mantus and a good thought provoking post.
I have some ideas and will share later.

Peter,
I don't think it would be difficult to bring reality to the surface in a lab or other scientific and objective means would be easy enough. But we're just talking about anchors and high tech labs aren't available for anchor research. We're just pulling anchors around in the mud or dragging them up on a beach in not very universal or specific circumstances. I intend to cut the roll bar off of my Supreme and drag it around some and see if changes anything for the better. Not only will a repositioning of the center of drag result but the CG will also change. However that's not the only modification I'm going to make.

But I disagree w you Peter. Not much speed is required have large effects on the drag of anchors. Actually almost no movement at all in a fluid like a seabed w an anchor buried. What I think you may be thinking of is the fact that a vehicle in a fluid like an airplane or an anchor not only has drag that will try to change the pitch (up or down) but a stabilizing effect from the vehicle. Most tailless aircraft have little pitch stability. I have flown at least 4 or 5. Most airplanes have long tails and horizontal stabilizers (the winglike thing the elevator is usually attached to). And anchors have shanks and flukes not to mention a rode pulling them in a certain direction. Like a sailplane being towed aloft by another plane.The rode is IMO most likely the element that limits the effect of pitch forces having reduced effect on an anchor. Because of that the pitch force and the result will be small ... but probably having some effect on the anchor,'so ability to pitch down and penetrate the sea bottom.
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Old 09-14-2014, 11:58 AM   #397
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Recreational anchors, their reputations and their following is forged by real world experiences and not theories or tests.

Sub-sonic aerodynamics and water and mud have little in common when used in gross generalities as air is compressible where water and solids virtually aren't....plus speed certainly has an effect on drag in most situations.

Comparing the 2 is beyond my comprehension as a longtime Naval Aviator and Mariner.
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Old 09-14-2014, 12:45 PM   #398
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SNAME, API, classification societies, military, and insurers have built all sorts of test rigs and devices used to design and model drag embedment anchors.

To say it can't or shouldn't be done is not true. But to make a business case for it is different all together.

For the real anchor geeks, take a peek at the Vryhof anchor manual.

I think the future of anchoring will be due to those that take advantage of the step changes occurring with sonar to identify the soil and substrate to choose the proper anchor for the conditions.
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Old 09-14-2014, 01:00 PM   #399
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IMO - Only boaters that REALLY need to learn about anchors and anchoring techniques are newbies. Old salts, such as most in this discussion/thread already have damn good idea as to anchor designs and anchoring techniques. I any old salt doesn't know by now... then, it is time they took up a new R&R sport... other than boating and "hooking"!
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Old 09-14-2014, 03:13 PM   #400
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Djbanji,
I've been saying the roll bar is not a positive thing. That it has some drag and that adds to holding power of an anchor but not nearly as much as a good fluke does. So I've been think'in other methods should be used to control the attitude of anchors. Hinged shanks work, ballast works and several other means have been used. The roll bar adds weight (at the wrong end (usually)) and it gives some roll bar anchors fit's in really soft stuff.

But in addition to the drag that is obvious I've said there is "interference drag". I've always thought it was not terribly significant but what if I'm wrong. What if the interference drag equals that of a fluke .. or even more. The Supreme and Rocna do perform very well on hard bottoms and I'm saying it could be the compaction between the roll bar and fluke that give them such high performance (in hard bottoms).

The Bugel anchor (as far as I know) was the first roll bar anchor and perhaps it's designer had compaction in mind. The hole or opening through which the substrate must go is small. Much smaller than all the roll bar anchors that came after.

Djbangi you wonder about the Mantus and it's very dependable performance that was'nt too bad (considering others like Rocna) in holding power either. So perhaps the roll bar is playing a bigger part in the actual holding power that I had thought. Is it possible that the large radius roll bar like the Mantus and SUPER SARCA has a greater degree of compaction (interference drag) because of the larger opening through which the substrate must go. Much much more substrate is forced through the opening because it's so large. Just like a larger dia prop works on a greater amount of air for more efficiency.

That could (remotely at least) help explain a larger roll bar performing better but the most significant thing that the test revealed about the Mantus is not holding power but dependability and consistency. Usually (IMO) that is more important than holding power. Both, of course is the holy grail but if 90% of anchors provide enough holding power then I submit that dependability and consistency are probably more important. Then (at least) the holy grail is attainable just by getting a bigger anchor. This is what I generally had in mind when I bought the Claw last fall. What I had in mind of course was flawed. But not terribly off the Mark.

But if the compaction function is considerably more effective than I had thought there could be more roll bar anchors in the future rather than less. And less is what I thought was best until I thought about the above.

Also the compaction function could play it's role in anchoring in other than roll bar designs. Consider a old iron rake w all it's teeth. There'd be a whole lot of compaction between all those tine's. Hmmmmmm
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