Catamarans for tuna fishing

[Mike King]

Samoa has a growing tuna longline fishery in which aluminum catamarans are
the main vessels utilized by the local fishermen.  The tuna fishery is now
the biggest export earner in the country.  As the industry has grown so
quickly many local boat builders have constructed vessels without
following approved plans from marine architects.  The government is now
requiring that all fishing vessels are surveyed.

What we would like to know: is there a formula for determing the beam size
holding the two hulls together in relation to the boat length?  For
example:

a 8.5 m catamaran might require 10 cm by 10 cm beams and
a 9.0 m catamaran might require 12 cm by 12 cm beams
etc

Grateful for any info.  Peter Watt