The Challenge The Thirsty Knights of Norfolk and the Belfast boys Hairy Hogs go head to head as two teams of bikers battle it out in a race across a lake in their scrappy craft. They must rescue their stranded expert before returning safely to dry land and, hopefully, a place in the final. Hairy Hogs The Hairy Hogs sailed into the semi-finals by scoring a victory over the tree-hugging recyclers The Hogs are three fun-loving bikers from Belfast. Captain Conn Kelly, Darrell Hanna and Alastair Nethercott combine the talents of an electrician, mechanic and a plumber and are all members of the same Harley Owners Group. Big men, with personalities and hearty laughs to match, they are up for most things – except water-based challenges. So having come through the Jet Boats challenge, they'll be hoping for terra firma this time. Ha! Helping them is Simeon Oakley, a freelance designer/fabricator who has built a wide range of marine vessels, from boats to hovercrafts. Born in Woomera, Australia, on a rocket range in the desert, Sim grew up in Saudi Arabia on an RAF base and went to school in North Wales. He has worked for a circus, designs and builds interactive exhibitions for science museums and lives on a restored Thames barge. He's a great engineer, he's a very cool customer and he's quietly confident. The Thirsty Knights The last time we saw The Thirsty Knights, they were gliding past Honda head-honchos The Fireblades in their flying car. Captain Pete Twissell, a design engineer, his brother Frog (yes, that's his real name) Twissell, who is a Buddhist and a vegan, and welder Carl (Roo) Verlander are The Thirsty Knights. This team is quirky, alternative and very intelligent. Yet another team who love their bikes, they have owned, built, raced and maintained many over the years. Used to thinking laterally to get around a problem – they love designing the weird and wonderful. What they produce will be a creation in every sense. Joining them for this boating battle is Bill Rutland, an East-End boat-builder and engineer who has spent all his life working and living on the docks around Tilbury. Bill's firm, SEMEC Engineering Ltd, undertakes a variety of jobs from maintaining boats and barges to engineering specialist pumps for Thames Water. Bill is even building his boat from scratch as a hobby. So far, the 48-tonne craft has taken three years. His practical skills, engineering nous and years of expertise make him an ideal expert. The judge This week's judge is Commander Steve Farrington who has spent a lifetime in the Royal Navy as a marine engineer and is an expert in amphibious ships and landing craft. Currently with the Royal College of Defence Studies, he has been posted to many ships, including the aircraft carrier HMS Hermes, the assault ships HMS Intrepid and HMS Fearless. With that experience, he is the perfect person to preside over this challenge.

• Lisa Rogers
• Dick Strawbridge
• Robert Llewellyn