Cav plate length...

Is there a way to determine the best length for a cav plate? I'm getting ready to build some for my 19' Spectra and don't know how long to make them. Looking at running 100+ with lots of power if that makes a difference. Sort of a GN style hot rod ski racer river cruiser whadayacallit...
Plan on using 2024, not sure if 3/16 or 1/4"...
Thanks in advance...

Cav plate length...