Both fine Australian designers. Tony Grainger's boats are generally pretty, well proportioned, round bilge
I assume by Crowther you are referring to Lock (who is now dead) and not Brett his son who I think no longer designs sail cats. Locks boats are fine, well engineered vessels. Generally foam and Glass construction whilst a lot of graingers are wood composite.
The only catastrophic failures that come to mind for either designer
was a float falling off Graingers "ocean emu" tri en-route across the gulf of carpentaria and one of the first "southern ocean 50" designs by Brett had a hull
fall off en-route Melbourne to Sydney
. Both failures occurred in light conditions.