Hi Mar
There are some cruising cats that do have that type of sailplan --large jib small main ,-it may be what the designer had in mind --jib efficiency ,-that along with moving the mast aft which reduces the pitchpole tendancy --in effect more bow length forward of the mast and center of effort on the sails . -Balance of sailplan C E to hull and underater profile center of lateral resistence CLR are always key in any sailcraft design , --balancing the rig location and rake to helm .--Generally the C E leads the CLR by 10 to 15 % dependant on sail shape and hull type as other factors also .
To answer the question of aft mast and jib only ,-With an aft placed mast only there is still the drag of a 30 ft plus mast ,-placing a main on it to add sailarea and make use of it makes design sence , better than it there doing nothing but holding the forstay and large jib .
A very areodynamic light A framed rig configuration with both main and jib set on a wire in betwen the two masts is an intriging design concept ,
The efficiency of the rig would be similar to existing wing type sails as on C Class cats but potentially much lighter and less complex or prone to damage ,-the key would be designing the A frame sections to be pivoting and efficent and lightweight enough to overcome the drag ,-maybe the C F materials and great sections as we see on the A-Class cats now make this a possibility ,-
One rig configuration I really like for its simplicity is the ancient Dhow type rig ,--basically what is used on the sunfish sailboat today , a short mast with longer angled one with the sail attached for raising and lowering ,-been around a long time .--The angle helps create lift ,-we generally see these rigs set well forward ,-the dhows sometimes add an extra smaller same sail set aft .
This would be a great rig for a cat ,--the catyak used one .
Some fun ideas for the other armchair cat designers out there ,-
Carl