Rented a five person motor boat here for a couple hours. It's super low power -- they don't give you the powered up ones without a driver -- but plenty of fun for a couple hours tooling around the harbor and giving the kids a shot at the wheel.
We started at 10:30 and the water was great for the first hour, then got very rocky by 12 so we headed in. Apparently that's normal, so with a boat this size I would definitely stick to morning.
These guys also rent jet skis and offer all sorts of guided tour activities.
Also worth noting though: it's pretty far from town, so you may want to check for similar offerings in Port Olympic before choosing this one.
Also note: check into your own life vests before driving off. I asked about ours and they said sure, it's right in the trunk here... oops, guess we better get you one. read more