What is the floating dock made of ? If it has a wooden deck, perhaps you that build a stand off stand that will enable you to have the rub rail at the top of the hull be your contact point in lieu of the area near the waterline. Two 4x4's held in position by a frame of 2x4's bolted to the deck and properly braced would do the trick. I don't think fenders alone will keep the boat from riding up onto the floating dock with the freighter waves you are talking about. Just my 2 cents,
Kevin
Kevin