I took the river bus again home, which was fun, like this (only more fun, this was a slow bit):
Up by Chelsea Harbour saw what looked like Batman's speed boat: This was Earthrace - in London for the Thames Festival (which very very unfortunately I will miss due to a business trip). As you can read here, she is a biofuel powered boat designed to race around the world. While this sounds very eco friendly, I am very skeptical about current biofuels. They rely too much on primary crops such as grain or palm which dramatically increases humanity's need for land, leading to huge habit loss and likelihood of wide scale extinction (as described here).
If you want an eco-friendly race around the world there is really only one answer - use a sail!