The downtown boathouse is located on Pier 40, 72 and 96 in Manhattan. It is operated by a group of volunteers who love kayaking and (I think) want everyone to experience the joy of kayaking.
The whole thing is free and they provide all the equipment, and teach you how to do it. You can kayak for 20 minutes at a time (then you have to bring the kayak in and wait in line if you want to do it again). They do this to make sure everyone gets a chance to kayak. The only thing I didn’t like much was that you can only kayak in an an enclosed area in the bay. They don’t let you out of it. They do it for your safety but still!. Oh, and they have single kayaks (operated by one person) and double kayaks (which are operated by 2 people).
They also take you on 3 hour guided tours of the hudson river. The only requirements are that you be physically fit (as you have to paddle for 3 hours straight) and that you know how to swim. The tour begins at 8:00 AM so you have to be there pretty early.
For more information, you can visit their site at: http://downtownboathouse.org/