David Tyler wrote:
Thanks to discussions on the OCC forum, I've come across a series of videos of anchor tests that throw a great deal of light on how anchors behave:
https://www.youtube.com/channel/UCy1Fn_m9nfcf4asEG_bulHA
Of particular interest to me were #63 and #67 in the series. #63 deals with the Rocna anchor, which grabs the bottom very quickly and reliably on the first set, but can drag when the pull is reversed and the anchor resets (at a windshift or change of tide). I've found the same, very occasionally, and apparently it also applies to the Manson Supreme.
#67 goes through a series of modifications in an attempt to improve a Manson Supreme. It turns out that the cause of the problem is that a big clod of sea bottom attaches to the top of the fluke, and it is this that inhibits reliable resetting.
There are commercially available anchors, from http://www.anchorright.com.au/ for example, that have perforations in the fluke - and it is these that make a dramatic improvement in the anchor's ability to shrug off the clod of sea bottom and then reset reliably. I'd never have thought of that in a hundred years.
I haven't the data to watch the videos. However, in the 'for what it's worth' category, Alan reports that
Zebedee has dragged his Rocna on at least 4 occasions.
I never had a problem in the years I lived at anchorw on Fantail, using a Manson Supreme in tidal waters. So maybe it's a bit horses for courses. For that matter, I never experienced Fantail misbehaving at anchor, either, like Bryan describes: indeed, I was always surprised about how docile she was. On the other hand, I always tried to anchor in less than 10m of water, so that I didn't have to resort to putting out the horrible three strand nylon, that passes for anchor cable here. (BTW, I see that finally Burnsco have started selling eight-strand anchor rope.) Bryan's description would appear to bear out my prejudice!