Delon nearly killed in yacht scene?

On first viewing I couldn't figure out why Ripley threw himself into the water. He was barely able to get himself back onto that boat, and I thought, very believable acting job, Alain. Then a very astute film critic pointed out that the sail boom cracked Delon on the head during the storm scene and came close to killing him. It was just cinematographer Henri Decaë and Delon on the yacht and they both were pretty scared, as the storm scene was not planned and the director went with it.
On repeated viewings it still seems like he jumped, but I think it was just the momentum of the boom swinging across that sent him flying.