I've spent many, many nights in Grand Case and the wind
can occasionally funnel through the cut in the mountains along the runway and hit the boat with gusts far beyond the normal winds speeds. One can be over a kilometer out of the Grand Case when the water
goes down to below 20 feet, and close to shore where the ferry dock
and Calmos are the holding is excellent with 10 feet of water
and sandy bottom and I cannot imagine an 8:1 scope dragging unless the anchor was set in one of the grassy patches. Aside from some uncomfortable nights in high winds and two or three days where I missed the weather reports of a north swell setting in, I love the Grand Case anchorage and will be sailing for there tomorrow (from the BVI).
too far towards the Grand Case Beach Hotel
and Octopus Divers is not always a good idea, as the winds tend to swirl around the hilltop and you can easily get backwinded in that part of the anchorage.
Anse Marcel is well-known (or infamous) for swirling winds and if there's any weather on the forecast
then I avoid that anchorage - plus it is not particularly well-protected from swell.
Both those anchorages are not typical of the Caribbean; they belong to a short list of well-known potential problem areas. Basseterre on St. Kitts and Saba
belong to this list as well. What is quite important to note is when a north swell sets in most normally acceptable or protected anchorages are no longer such.