At the Kabetogama Lake area of the park, they have an NPS boat called "The Otter" that takes you on the ranger sponsored tours. I took it to the Ellsworth Rock Garden. It was comfortable enough and ably captained by CPT Al.
Many people bring their own boats (I don't own one) to explore the park and its islands and waterways. All four parts of the park have parking for the boat trailers, boat ramps and lots of dock space.
At Rainy Lake, the NPS boat is called "The Voyaguer). It will take you on a variety of ranger-led tours. For me, that will have to be next trip.