“I WAS AT MY smartest when I was 11,” said Matthew Friedberger recently, “and I never really got any smarter.” Little wonder, then, that the second album by Friedberger and his long-suffering sister Eleanor often sounds like the work of preternaturally brainy, hyperactive children.

Gallowsbird’s Bark, their 2003 debut, suggested The Fiery Furnaces were a playful garage-pop band with an unusual surfeit of ideas. Blueberry Boat, however, is an extraordinary leap into the wide blue yonder, where every song contains at least three great pop tunes battling for supremacy. At first, it seems like an epic self-indulgence; Matthew’s short attention span played out on a preposterous scale. It lasts 76 minutes, and several songs stretch beyond eight. But the Furnaces rarely stick with a theme beyond 30 seconds. Instead, they build collages where genres are haphazardly stapled together: nursery song, manic carny music, the interlude themes at hockey games, prog, indie rock, Beefheart, The Who, Pavement, crotchety electronica and, frequently, avant-garde sea shanty.

Gradually, the Friedbergers’ method reveals itself. While their debut was informed by Eleanor’s international wandering, Blueberry Boat is the product of Matthew’s imaginative crunching together of history books, old maps, the glossary to Moby Dick and a vivid, detailed nonsense vision that’s like Edward Lear relocated to Brooklyn. His point, he claims, is to create a history of American travellers. Blueberries are the quintessential American product, and the blueberry boat symbolises cultural imperialism.

The Furnaces, though, are too entertainingly impatient to keep their allegories tidy. As the music relentlessly shifts, so Eleanor and Matthew’s deadpan duelling vocals trip off on endless digressions: the blueberry boat is attacked by pirates on the South China Sea; European Championship football fixtures confuse American sales reps in a Damascus cyber-cafe; “Little tender-footed crabs meet my knuckleduster.”

It’s a lot to take in. And sometimes, as another brilliant tune (“My Dog Was Lost But Now He’s Found”, say) flies past with lunatic haste, it seems they can be eccentric to the detriment of their own songs. Persevere, though. What initially resembles a mess slowly crystallises, after six or seven listens, into a polyhedric and endlessly fascinating album: bright, daft, wise, infantile and far more memorable than one would ever have guessed.