Cool... I've heard of these but have never seen one. I assumed they'd be pretty heavy. But I dug down to find the Design Report for the 2001 UAH boat and they're not that bad... I think you could find 22 ft. wood/FG kayaks that weigh more than this (not that I've ever built a 22ft. kayak - but I'm afraid to weigh my 17 ft. Arctic Tern!). Here's an excerpt:

"Our boat is 6.8 m (22.3 ft) long and has a mass of 34 kg (equivalent to 76 lb), a maximum width of 81.3 cm (32 in.), and a maximum depth of 27.9 cm (11 in.). A 757 kg/m 3 (47.3 lb/ft 3 ) concrete mix, having an average 7-day tensile strength of 1.77 MPa (256 psi), was used to produce the hull."

: Wonder what these guys use for backup floatation?