When I first bought my CC19 (September 2008) the largest concentration of boats seemed to be on Rutland Water. I am not sure that this is now true.
We now have five CC19s on Kielder Water, in order of longest time time first:
Mary Ann
Bernicea
Moneypenny
Falcon
Nemo
It would be useful to know about other concentrations when considering venues for possible events.