Hi,
he has done these measurements with both hulls in the water. Drag trough the air for the wetted surface normally in the water is less when flying a hull (due to the much higher density of the medium the hull is moving trough when flying).
His point tough, and the reason for the article, is that his Tektron 50 design with rounded hull-deck joints offers less recistanse (drag) when going to windward and thus are a superior design. (Both hulls in the water of course, and this is the basis assumptation for his findings)
On the same grounds, you could round off the hull-deck joint on your smaller multihull. But you would probably be better off wearing a full-body swimming suit and lessen the drag of your own body trapezeing
Short version: One hull flying is faster (both hulls flying are probably slower)
Read the article from Shuttleworth carefully, and I think you will se that your question is probably a bit out of context (no offence intended!).
