On Ariel 414, the dimensions are (qualified with I don't know if the sole is original or how much variation between boats):

Forward sole:
Length : 29" (from base of porta-potti deck to bulkhead)
Fwd Width : 13.5"
Aft Width : 26" (widest section)

Cabin sole:
Length : 63" (from fwd end to base of trim at companionway)
Fwd Width : 16.5"
Aft Width : 18.75"
Widest section: 22.5"

This is the actual decking, there are a few inches of fiberglass on each side before the base of the seats.