Several posters have apparently had some trouble getting a spade
anchor to set. There was a discussion just on 8/11/04 in this
newsgroup about that. See BVI Anchor Test - Glenn Ashmore

The conclusion was to let the spade sit and dig in on its own for a
little while before trying to back down with the engine. Those who
drop the anchor and just let the boat fall back with the wind seem to
be successful. Waiting apparently lets the heavy point begin to sink
in on its own.

I do not have any personal experience with this. I am just repeating
what was recently posted.

Lee Huddleston
s/v Truelove