You feint towards the cannon, then take advantage of the thugs scattering to dash across the gangplank that they'd been guarding. You navigate the tunnels towards the Foe Reaper, hearing your pursuants' cries become fainter. This gives you enough time to jump into the Foe Reaper when you get to it and boot it up before the thugs reappear.
Kill the thugs using the Foe Reaper's built-in weaponry. You are in possession of an extremely valuable and defensible piece of goblin technology. Leave in it.