Its a 'J' grapnel, for recovering lost anchors or other items from the seabed. This one snapped under the enormous strain of pulling aboard the anchor and half a kilometre of chain. You do not want to be in the way of something like that, the inertial forces must be astronomic.
And lastly here's a view of one on the deck to show just how big these things are compared to that tiny bloke behind it! The anchors weigh up to 35 tonnes and the J grapnel can be 5 tonnes.