That is just the question isn't it.

Powerboat cats are all designed the plane

Sailboat cats (like ORMA 60's) are designed to sail in forced displacement mode.

Only exception the latter rule is the Yves Parlier "seaplane" catamaran "Médiatis Région Aquitaine"

This cat has been pushed hard for 4 years now and not proven to be a winner.

Also of interest is this little bit of info as contained in a press release :




Source : http://www.ybw.com/auto/newsdesk/20040104160707ywnews.html

So indeed it is not a black and white situation. With each design you need to look at the specs and operating point to determine which of the two (or three) paths available is the best. For racing sail powered catamaran the paths most favoured are forced mode displacement and indeed foiling (L'hydropthere, longshot, Techiques Avancee).

A while ago I had discussed planing hulls with some A-cat designer and he replied that they had tried during the 80's to make it work, but failed to beat the normal hull designs. One issue was to keep the hull planing smoothly. Typically the boat would drop off the plane when heeling or pitching due to a gust. This could well be one of the more important reasons why powerboats are all planing designs were sailing cats aren't. It is easy to keep a powerboat "flat" or tilted at an optimal angle.

Wouter