Frenchie,
"if lateral gap is under 30% rigs span "
I am unsure what you man by the terms lateral gap and rig span.
Does this mean if the distance between the masts is under 30% of the boom length?
Thanks
Gareth
P.S. here is another good looking biplane boat
http://www.mko.freesurf.fr/innovoile/historic_e.html