It's an initiative proposed by http://nomadedesmers.org/ (French - google translate in the footer)
16 karma · joined November 12, 2009
Concerning the depth, it's indeed a very important aspect of the chart but in my opinion it's by far the most difficult to obtain with crowdsourcing. The guys at Openseamap seem to have made a piece of hardware just for that purpose (http://www.ak-modul-bus.de/cgi-bin/iboshop.cgi?show1100,5708...).
Keep on the good work guys, we need an open source solution for naval charts. Thanks.