-Really enjoyed the pics from the Paris boat show Wout thoughtfully provided ,-and really enjoy design related discussion of new ideas. The new boats are fasinating ,-and look well designed .2 sent e mail on this topic ,-both know more than I do ,but will try to define the ideas drawn out for this type of planning cat design that I have just for fun..hey they asked for it .
The intricacies of design and how they relate to one another is difficult and in rating boats even using a sophisticated cad design comp 3 d modeling and performance prediction type programs now available ,-it is still the big unknown quantity,-
How well do design aspects interrelate ,--mast to sails to variation in shapes -to volume calc -C E to CLR -handling characteristics ,-tuning and boat handling by skippers of different ability. all unknown and subject to endless refinement.-Any cat design is subject to this type of needed refinement and improvement as part of the process.

Basic current thoughts on planning cat design are
1-basic hull -The need for more canted hulls that place the flat lifting bottom hull at optimum angle just beyond designed heel angle that result from sail forces at work and resulting heel angle are key , This varies dependant on beam and hull volume, and planning ability .
If a typical cat w 8.5 beam is drawn out at a sailing heel angle with the windward hull skimming the surface its is approx 12 degrees , more in waves ,--More hull cant is required than this min. due to side forces and keeping the hulls on plan once there. You do not want a hull type that falls off plane.--This is one main problem with the pure foilers .
2-allignment of hulls in relation to one another , -
Canted hulls do not allign . Bow down tendancies of cats as they accellerate with wind-sail forces are the problem . A canted design with deeper bows will become more mis alligned causing form drag, once one hull lifts ,no problem ,but at lower speeds a large problem . We have seen some C Class designs with a destinctive toe in look for this reason .-The other direction for canted hull design is more volume and less depth at the bows as we see in some newer design with canted hulls .The Inter line is an example .This lends itself to developing the planning hull.
Balance and lift --
Sufficient flat bottom hull area at correct sailing heel angle being designed in may be assisted by a small forward foil or board ,-it may be retractable or molded in , pictured as an extention of the bottom angled hull back from the bow ,-It would require a swept back leading edge to avoid damage and enable beach landing . Standard boards further aft would provide tracking ability as in most design though further aft to balance CLR with forward foils.The leeward working foil would provide added lift and the windward would provide some resistance with its reverse angle . This more forward CLR with back boards partially raised when under chute should allow a more forward position of it in sailplan and still balance the helm well. Key for the skiffs is a higher luff angle set on longer spin poles that help provide more lift from the chute .
Multiple benifits from the extended forward foils.

This type of cat should track in a straight line well and have sufficient side resistance from foil boards rudders and L and v shaped straighter hull lines.
More mast rake in the design is important and hull volume aft to carry crew weight with more straight line profile more consistant with planning powerboats is needed ,-though am unsure to be honest. More beam -wings or rakes with more power in the sailplan are the huge advantage multihulls have over monohulls that just tip over without this stationary initial stability.
A larger dagger type retractable rudder may also be a needed part of this planning type cat design for added control and balance options , I like the through hull type with a wide flat planning stern would look good and be very strong and simple ,-2 moving parts-- the rudder and circular hull section fitting it slides into .Think the Olsen 30 uses this currently.
Again this fits into the intricacies of this type of hull design .
This type of larger balanced rudder may be able to take the place of aft boards in some design applications .It would reduce weight and -area further.
Light weight is crucial along with all other elements of proper design ,--just a hobby of interest for me but always fasinating to talk design ideas.

Please add your ideas to it .

Have fun
Carl