For the boat trip, on the Thursday, boarding is at 1745-1800, at Westminster pier, and we return at 2000. Our boat is the London Rose. There will be a bar, and the first two drinks each are free. The pier is a 25 min walk from the RAS, with different routes shown below. The dotted one through St James Park should be the nicest. When you get to Westminster Bridge, turn left and you should see the entrance to the pier, and then you need to identify the boat pictured below. 

Alternatively you can walk along Piccadilly to the Green Park tube station and take the Jubilee line one stop to Westminster. The pier is right next to the south exit.