Depends. In most situations a ship will drag her anchors along the sea bed, but if the anchors catch a strong hold on something like a massive rock, or a shipwreck, then it could do some serious damage. Having said that, the POR's anchor chains and winches e.t.c probably wouldn't be strong enough to pull her under, since they'd have to be strong enough to lift the whole ship in the air in order to overcome her displacement. But an anchor could probably roll a ship onto its side in certain circumstances, if the anchor was down on one side and the ship was moving at speed.