Here's one for Eddy. I fully expect to see a fully operating model at the 2010 Paddler day.
Just back from a holiday on Lake Trasimeno in Italy and found this gem moored in the harbour. It has cutters and a conveyor belt to clear weed, which can be a problem on the lake, into a large hopper. Couldn't believe my eyes when I saw the paddles but I suppose it makes sense, no weed tangled round a prop. The paddles probably cut any weed to ribbons.
Meant to go back with a measuring tape and get some dimensions but unfortunately didn't have time.
Some taster pics below and lots of detail pictures on Photobucket, see montage below.
http://s669.photobucket.com/albums/vv59/carmanmole/Paddle%20Dredger/