Ash is definitely the wood of choice for gunwales. It is hard enough to take a beating, relatively rot resistant, inexpensive, glues up well if you are scarfing two pieces together and takes a nice finish. Most importantly, it will match the seats if you purchase them commercially made as most of them are made of Ash.

For a job like that I would consider using dowel pegs for a through and through of the inner and outer gunwales as the hull is likely made of polyester resin which is horrible to glue to. A through dowel epoxied every 12" or so will work well and be attractive.