I am not surprised you were surprised: it is, unfortunately, not widely disseminated information. And do not get me wrong: the Rocna classic (with a roll bar) is a far more effective anchor than say, a CQR or a Bruce, especially in a straight pull after being set; which is the case for most anchoring situations. And it can and does re-set, but it is not consistent and when you need it most (a sharp change in direction and pulling along the bottom at speed), it may fail to re-set. A slow re-set, likely in gentle winds where the anchor is allowed to settle, a re-set is more likely.
And your Scottish fishermen friends were quite accurate in pointing out that weight is a big factor in getting penetration through weeds and kelp to the seabed. This may help explain why a Spade anchor is so effective with its tip filled with lead and concentrated at leading the anchor through the weeds and into the seabed.
But, I do disagree that anchors will drag at 50kn+ wind speed: a good anchor may creep some, especially if it is the “recommended” size as per manufacturer. My experience is that, for cruising boats, one should be one or two sizes above recommended. (I actually recommend that one’s bower also be one’s storm anchor: too often a storm anchor is buried deep and hard to deploy and many storms are squalls and the like which come on unexpectedly and give little time for preparation).
Firstly, I was using the anecdote as an example of two areas of concern for me in my writing: That problems or bad habits in new and exciting gear and systems often take years to emerge, and:
Secondly, I wanted to do a little rant about the marine industry and their unwillingness to flag practices and gear that may be problematic.
(I am only talking about the Rocna with the roll bar, I believe the jury is still out with regards to the Vulcan, which I believe was developed, in part, as a reaction to the classic Rocna re-setting issue, and, in part, as a response to Spade’s popularity and effectiveness). With regard to Rocna’s occasional bad habit of not re-setting after a wind shift or current change if in a tidal flow, I know of this proclivity from direct reports from skippers (and friends) where this has occurred. I know Practical Sailor magazine in the US has also expressed concerns in this area and may generally be speaking of those anchors with roll bars.
The fullest report on this issue (that I know of) is on fellow OCC member John Harries’ Attainable Adventures Cruising web site where he collects and opines on the subject along with many experienced skippers who weigh in with their thoughts and experiences. It will cost you~~$20 for a membership, but if you are fitting out, as you are, for offshore passage making, I believe there is no better place to gather a wide range of thoughts on all aspects of offshore wandering by sailboat. The membership will more than pay for itself, I expect, quite quickly.
For a striking example on video of the Rocna re-setting issue, go to SV Panope (https://www.youtube.com/watch?v=WL9JL9AK6ss
might be a good place to start) where there are also great videos of a wide variety of anchors setting and re-setting in various bottoms very creatively done.
My best, Dick Stevenson, s/v Alchemy