The quickest way to start a brawl is to walk into a bar full of sailors and yell:
Who believes that chain catenary improves anchor holding?
The fight usually breaks into two opposing gangs: those who believe that having a lot of chain on the bottom increases holding, and those who have actually observed an all chain rode being pulled bar straight in strong winds who cry "bullshit".
But the reality is much more nuanced, and understanding that can help us anchor more safely...and avoid bloody noses in bar brawls.
Let's turn our attention to the former: how to use catenary to help us anchor, and when not to rely on it.
The Governing Theory
First off, a bit of theory. I'm sure most of us know this, but it's worth revisiting, because it's the basis of everything else I'm going to write about:
(By the way, Danforth-type anchors, including the Fortress, are, as far as I know, the only exception to the rule. They set better if the stock is lifted off the bottom a bit.)
Let's leave ultimate holding out of it for a bit (we will come back to it later) and focus on setting.
There are three ways we can decrease the pull angle and thereby help our anchor to set:
- Increase the scope.
- Increase the catenary.
- A combination of both.
I'm going to dive into all three in more detail, but first a story.
A Lesson Learned
About 20 years ago, we changed from a CQR to a SPADE anchor, both set on 7/16" (~ 11mm) G40 (high test) chain. The new anchor worked so well that we got a little slap happy about our anchoring technique:
- Drop anchor.
- Let the chain run to 5:1 scope before putting any load on it.
- Wait for the breeze to straighten the boat out.
- Back down hard to set.
- Have tea.
In thousands of sets, over some 15 years, from the Bahamas to Greenland, our SPADE only failed to set a few times, and we never dragged it once set.
Then, six years ago, we changed to 3/8" (~ 10 mm) G70 (heat treated) chain, both to reduce the weight in the bow and to increase the amount of chain we could carry from 340 to 400 ft (103 to 122 m)—in the high latitudes, where anchorages are often deep, there is no such thing as too much rode.
Suddenly we were experiencing more failures to set, particularly in soupy soft holding. At first we were totally perplexed. What the heck? Had we forgotten how to anchor?
And then the light went on:
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