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Old 14-07-2013, 20:06   #61
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Re: Anchors and Chain

That was an interesting read. I had previously not been familiar with the term "Catenary".

The popular wisdom that I have always encountered is that you need enough weight in the chain to achieve an asymptotic curve resulting in a nearly horizontal pull on the anchor. I think that pretty much all of us can agree on that much.

I have long encountered debates on the advantages of long pieces of thin chain vs. short pieces of fat chain. How much is enough obviously varies with vessel & conditions. Beyond that, much disagreement generally occurs among the people that I have known. My personal preference tends towards short fat chains for ease of handling, unless I am going to be in an area with a lot of sharp coral where chafing is a major concern. But that is just me.

I have never sat down to calculate the optimum chain requirement for a given set of atmospheric condition because I have no way of knowing what I will encounter in the future. For this reason, I have always just looked at other boats around me, seen what did & didn't work well in various common conditions & then made a judgement call.

What I don't see being discussed here is the use of chum weights (aka angles, aka sentinels). I find that a dead weight tied to the anchor line, about 10% short of hitting the bottom, tends to make most anchors work much better. It also shortens up on the amount of scope that I need to use, unless it is REALLY blowing hard, & even then it still acts as a shock absorber to some extent.

I first started using chum weights when setting marks for sailboat races because having the anchor line go pretty much straight down helped to keep the keels from catching a line during a tight rounding. After a while, I noticed how well small anchors were holding large marks in a good blow, so I started trying the same trick with boats as well.

Does anyone else weight their anchor line upstream of the chain?
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Old 15-07-2013, 08:23   #62
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Re: Anchors and Chain

Kellets are frequently recommended, especially on mixed or all rope rides.
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Old 15-07-2013, 08:51   #63
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Originally Posted by pbiJim View Post
I find that a dead weight tied to the anchor line, about 10% short of hitting the bottom, tends to make most anchors work much better.
Well, as ever with anchors the problem is - how do you know?

As far as helping with keeping the chain on the seabed there are some spreadsheets in here..
http://alain.fraysse.free.fr/sail/rode/rode.htm

In that respect when things get a bit exciting it doesn't actually help much.
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Old 15-07-2013, 14:48   #64
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Re: Anchors and Chain

I like the principle of the kellet or sentinal, but their function would be most needed in strong winds or current and these are the very same times when it can be important to quickly retrieve your anchor and reset or move. With that in mind, their presence adds a complexity that slows the task in an emergency.
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Old 15-07-2013, 18:15   #65
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Re: Anchors and Chain

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Originally Posted by conachair View Post
Well, as ever with anchors the problem is - how do you know?
Precisely.

Two cruisers chartering identical boats are anchored in three fathoms with 150 meters of chain out. It starts blowing Force 8. Cruiser A, having read Smith's article, swears that his chain is "bar taut," without any catenary at all. Cruiser B is confident that the first 100 meters of chain lies on the sand, and says that he can feel it bump around when the boat sails its anchor.

Who do you believe?
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Old 15-07-2013, 18:47   #66
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Re: Anchors and Chain

I feel dense. How could one guy think the his 450' of chain is bar taut and the other think his is all normal? Guess I would believe B. After all 25 to 1 is a pretty good scope.
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Old 15-07-2013, 19:48   #67
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Re: Anchors and Chain

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I like the principle of the kellet or sentinal, but their function would be most needed in strong winds or current and these are the very same times when it can be important to quickly retrieve your anchor and reset or move. With that in mind, their presence adds a complexity that slows the task in an emergency.

These days, I'm mostly on boats in the 24-30' range. On those, I usually employ about a 15 pound chum weight about 10% shy of the bottom & then have about another sea depth of line before the chain begins. This rig allows me to haul up the chum weight & have it on deck before I start to feel the weight of the chain or the anchor. It really doesn't add much difficulty to the process. Did you envision using a larger weight or a shorter line to the anchor? I'm curious what rigs others use & why they favor them.

My above descriptions are for moderately winding conditions in congested, but not overcrowded anchorages. Of course, circumstances can dictate the use of more aggressive ground tackle rigs.
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Old 15-07-2013, 20:03   #68
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Re: Anchors and Chain

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Well, as ever with anchors the problem is - how do you know?
That is always an excellent question. I for one am a big fan of empirical testing. A few eons ago, Back around the 1980s or so, I spent a fair amount of time snorkel & scuba diving to inspect anchors & how they held. I checked every rig that was available to me at the time, which ranged from a cinder block, to a dead wood cross, to mushroom moorings, to various Danforths to navy style shankless anchors. I checked them with various amounts of chain included, from about 25 feet down to none. At the time, I had a fairly good understanding of how each of those performed under varying wind conditions in Nantucket Sound & Cape Cod Bay. Sadly, I did not repeat these diving inspections with modern anchors or in other areas with different bottom types, so my information is somewhat limited.
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Old 16-07-2013, 01:49   #69
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Re: Anchors and Chain

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Originally Posted by Bash View Post
Precisely.

Two cruisers chartering identical boats are anchored in three fathoms with 150 meters of chain out. It starts blowing Force 8. Cruiser A, having read Smith's article, swears that his chain is "bar taut," without any catenary at all. Cruiser B is confident that the first 100 meters of chain lies on the sand, and says that he can feel it bump around when the boat sails its anchor.

Who do you believe?
I would go for a dive and take a look.
I have done this so I think I hope that i can give a good real world view of what happens, although that is a lot of scope and I don't think I have ever seen quite that much in those conditions.

Beaufort 8 has the windspeed range 34-40 knots
34 k is definitely too low to lift all, or even much, of the chain off the bottom.
40 k is getting closer to windspeed range where most of effects of catanery are lost, but it is still a bit a too low and given the large scope I would expect some chain on the bottom, but not anything like 100m.

Even if all the effects of catanery almost disappear the angle of pull on the anchor is only going to change 4-5 degrees.

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Cruiser B is confident that the first 100 meters of chain lies on the sand, and says that he can feel it bump around when the boat sails its anchor.
If the anchor is reasonably set the chain attachment point will be buried and given the shallow angle of pull due to the scope many meters of chain will be on, or bellow, the surface even if the effects of caternery are almost lost and the chain is (almost) bar taut.

As the boat sheers around this will drag across the surface of the bottom. No one could distinguish a difference by the sound or feel of the chain even if the windspeed was sufficient to make the effects of catanery almost disappear
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Old 16-07-2013, 05:43   #70
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Re: Anchors and Chain

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Originally Posted by pbiJim View Post
.............................. It really doesn't add much difficulty to the process. Did you envision using a larger weight or a shorter line to the anchor? I'm curious what rigs others use & why they favor them. .............................
I guess I can't answer your question as I did not envision using a weight or line to the anchor at all. I discounted the plan to use the kellet or sentinal, not because of a difficulty, but simply because of the additional time required to remove the kellet before weighing anchor. On occasions, most often with the arrival of a brisk afternoon squall, I've been required to raise my anchor and move quickly to avoid either grounding, being set upon by another dragging boat, or being swept toward a lee shore. Some might be tempted to take this opportunity to recommend a change in my primary anchor or start anchor thread,- Please Don't! When I mention the occasional need to raise my anchor quickly; these events occur less than once a year while anchoring out often with fulltime liveaboard cruising.
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Old 16-07-2013, 06:44   #71
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Re: Anchors and Chain

I mostly used a kellet when anchoring Bahamian style, one anchor up current or wind and one at 180 degrees to limit the swinging circle when the wind/current switches direction. Most useful when anchoring in tidal creeks.

The kellet keeps the second rode near the bottom when slack thus preventing keel/rudder fouling.
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Old 16-07-2013, 11:57   #72
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Re: Anchors and Chain

I recently traded an 80 kg Claw for the same size Ultra and had an unusual anchoring situation yesterday that provided a comparison of the Ultra to the Claw.

Crab season opened yesterday and since we use rings, not pots, we anchor in place, throw the rings over and fish from the boat. Because we may leave after 30 minutes or so if no crabs seem around, we never put down more than lunch hook scope - like 2:1. Yesterday, we laid out about 1.75:1, but what was unusual was that we were in a short chop of around 2', which caused the boat to leap that much with each passing wave. Rough enough for my granddaughter to get seasick....

Even with such short scope and pretty good shock loads, the Ultra held very well. I think over the course of an hour, we probably did move a few feet, but what I thought was interesting was that we never broke loose. The seabed was typical PNW mud, which is pretty sticky stuff, mixed with some shells. Based on this limited data point, the Ultra seemed to do an outstanding job of resetting after shock loads in difficult conditions on very short scope. Winds were only around 20 knots, with the seas providing most of the opportunity to break free.
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