Take anchoring seriously and you can be secure in almost all conditions. Many anchors are only suitable for ‘normal’ conditions, they fail in strong wind or a difficult seabed. Anchor dragging is a menace in any anchorage, and it’s not necessary.
The new generation, high holding power anchors are a big improvement over the traditional anchors, particularly on bottoms with poor holding. But I suggest using a size larger than recommended for extra security when it matters.
The traditional chain scope calculation, using a simple multiplier, is not correct due to the curvature of the chain. 15m (50ft) plus double the depth is better calculation. But always put out more chain in challenging conditions.
Thanks to John Bellagamba for the Kata Beach video
https://youtu.be/tUAnOsqhJLo
and NauticTube https://youtu.be/Q93KUyEWkNc
Independent anchor performance test charts.
https://www.petersmith.net.nz/boat-anchors/independent-performance-testing.php
Lewmar Delta size chart
http://www.lewmar.com/sites/default/files/DTX%20%26%20Delta%20Anchor%20specifications.pdf
RYA - Things to think about when anchoring
https://www.rya.org.uk/newsevents/e-newsletters/inbrief/Pages/things-to-think-about-when-anchoring.aspx
Underwater Manson Supreme
https://youtu.be/wwaVD2KqitM
Thanks to Ultimate Ambient Noise Soundzzz for the ‘relaxing’ storm video
https://youtu.be/xytAfoU1d78
Caterary formula.
Chain length = Sqrt(2 x Horiz load x Depth/Chain wt + (2 x Depth))
Where Chain wt = Chain mass per unit length x 6.9/7.9 to allow for buoyancy
http://home.earthlink.net/~w6rmk/math/catenary.htm
Formula works for metric or imperial.
The catenary shown is for 10mm chain (2.28kg/m), with a 100kgf horiz load. This matches observations of the chain on our 45ft yacht in about 25kts of wind.