There would appear to undeniably be more drag with a foil. Basic proof: Slalom racers don't use foils.

A large surfboard does not have anywhere near the drag something like an AC Catamaran does, so won't benefit as much.

Windsurfers plane.



Note the other windsurfer near the end.

We could go even faster if we could magically get rid of the fin altogether. ...Macro?

^^^^ agree for a perfect like comparison you can compare yardsticks for the International Moth and Foil moth and speeds if you like.

Foils are Faster and create LESS drag........ even though windsurfers plane the total area near the back foot in contact with the water (including fins) would be greater than the total area of the foil....... I reckon anyway

i used to airchair waterski a lot and modified my own foils.
The speed record foils are a lot different. The waterski ones that the windsurf, kitesurf and big wave surfers use have horizontal foils bolted to a vertical T piece. Because there is a lot of surface underwater, they provide lots of lift but the drag gets a lot higher the faster you go. To a point where they becaome unuseable - it doesn't take much to max them out. The speed ones are probably quite high drag/ zero lift to start with, and only go fast because you can get a massive hull with a massive rig out of the water and just riding on foils. Windsurfing bigger is not faster
Everyone thinks they should be the future etc but there are lots of problems. I watch those surfers and windsurfers/ kitesurfers use them and roll my eyes. To ride them it's like balancing a chair. you can make them fairly stable, but if you get too high they will cavitate and you loose all lift and drop like a rock. the longer you make the vertical strut the more leverage there is so the bigger the potential kick out of the water (jump) but you have to temper that with control. They are very directional whan landing, and if you dont get it right its a massive stack. Nothing like landing a normal board and the freedom that gives. If you watch footage of any kite or windsurf related foiling they will be going along in a straight line. If you see a jump you probably wont see them ride away (chopped footage) it's because they ate it. The combination of riding the foil and controlling the kite would suck momentus balls IMHO, and I can land inverts on windsurf, kite and foil. I would hate to combine them. Also the skurfing style behind a wake boat would be pretty dangerous IMHO also.
Big wave surfing might have the advantage of skimming over chop (according to laird), but he can afford to dxck around and poo poo various conditions. They are just trying to cash in on the next watersport. Other than that I'd say it's going nowhere.

Kite board Foils are about to be mass produced, you could adapt this type to a windsurf board??

Johnny Heineken won the bridge to bridge race in San Francisco in September this year on a foil. Smashed the record by 2 minutes. It is definitely faster and for kite boards anyway, just much harder to stay on top of with out crashing big time.

Speed records held in some channel in Africa though they still use only fin for drive and are getting 55 knots plus board speed - both Windsurf and kite board - there are good link on youtube - check it out.