We had a fixed swim step on our Northsea 34. It was small, only about 2.5' across and maybe 1' deep. It made getting into and out of the dinghy a breeze. It was a bolt on from the factory, not sure if it would survive breaking seas on it. It was solid, cutting some slots in it would help I'm sure. For coastal sailing it was great.
You can kind of see it here