I actually find anchor
recomendations to be grossly undersized, and would always go up at least one step. The problem is that big anchors
are expensive, and everyone buys on price. So manufacturers recommendations are the minimum you can get away with...
In addition most anchor
recomendations are made for 50kn of wind... Since the force imparted by the wind goes up with the square of wind speed, what will work in 50 may not hold in 60, and will be grossly inadequate at 80kn. So unless you have somewhere to run too in the event of a major storm, a bigger anchor
is always better.
This is why for sizing I recommend the biggest anchor you can get back on board, like the Dashew's I am convinced an anchor isn't big enough until people start laughing at you. I also recommend minimal amounts of chain, and putting that weight back into the anchor. The cantenary effect in major storms is a myth, but massive anchor weight isn't.