FWIW, crossed on the ferry from Gravesend to Tilbury yesterday morning. The space for bicycles seems limited. I can't see them fitting more than 3-4 bikes on, but there was only one other cyclist on there (with a very nice hand-built bike). The ferry seems quicker but getting on/off is a bit tricky. On the Gravesend side they didn't bother with a ramp, which means a 30cm step to get on. The ramp on the Tilbury side is very steep on the new ferry as it's considerably lower down. The staff offered to help on both sides though.