Smith Eric Westerberg, from Umea, built the eight-tonne, 6m (18ft) "Isabelle" from scratch between 2005 and 2007, putting in an estimated 3,500 hours of work, Radio Sweden reports . Westerberg tells the PS auction house that he used "common sense" in the design after drawing a blank searching the web for blueprints. He says that he sold it because he no longer has the time to take it out for a spin himself. "It's fine to a depth of just over 10m (30ft)," he says. "It's hard to navigate down there but it's well-built and can take it if you bump into something."