We absolutely loved this trip - it was a great deal and brilliant way to squeeze nearly a full day in the middle of the park in only 1 day by boating in and out.
The details on the deal / website were a bit light when I booked so I was surprised to find it was more like a 9am - 4pm trip. Luckily we had extra time so it was fine. And well worth it. You board the boat in Kaiteriteri (either a launch or a small taxi depending on number of people - we had the small taxi which some didn't enjoy, and had no toilet), but it was a great calm day and the crew are just as professional and informative giving the same tour and commentary on the way.
They will stop by a few sights on the way up to drop you at Medlands beach, 10mins walk to Bark Bay. You then walk the middle part of the track down to a pickup at Anchorage. There is plenty of spare time for stops on the way.
You can arrange them to provide a lunch box for you or a pickup in Motueka, but I can't comment on these as we didn't use them.
We'd definitely recommend this tour to get into the middle of the park if you only have a short time in the area.