coco beds?

I have 2 600 w hps cooltube and 2 3x3 flood trays.
I was thinking of building 4 beds of some kind and fill them with coco fibre and water them with tropf blumat.
I want to make a sog grow with abut 15-20 plants in etch bed.

How deep do you think i need to make the beds?
and how many blumats do i need?

I haven´t seen blumats used in coco beds before so if some one has a link or some info it would be help full.

I think i will build the beds 30 cm deep but i still don´t know how many tropf blumat i should use fore 15 clones in one bed.
will 6 be enough? or do i need more?
all ready have 24 at home.

Plz some one that have used blumats before maybe can give me some input.

a bit of research and i found the answer on this page
http://www.rambridge.com/info/tropf2/blumatqa.aspx

NEED HOW MANY UNITS?
Outdoors: 1 Tropf Blumat can water a circular area of 30 cm (12"). FOR FLOWER BOXES WITH A WIDTH UP TO 20 cm (8") AND A LENGTH OF 100 cm (40"); you need at least 3 Blumats. A LENGTH OF 60-80 cm (30"); at least 2 Blumats. LESS THAN 60 cm; Use 1 Tropf Blumat (with a distributor dripper if water distribution is not even).

thanks any way.
peace