We are talking VMG during a foiling tack versus a non foiling tack.
There id no doubt fouling is faster between tacks.
If you watch a foiling tack from above you will see the helmsman drive the boat quite deep to get the speed to maintain foiling thru the tack. Also the speed in an out of the tack is not that much better for the extra distance, time, and angle, away from th top mark, they sail.
It could be a close thing.
I don't agrree. the main reason is that if you don't foil tack you have to lose a huge amount of vmg to get up on foils after the tack,especially in light airs; or at least this is what really makes the difference in moths;it's not the speed difference during the manouvre, but he vmg loss to get back up on foil if u crash down.
So I once worked out based on GPS traces a couple of years ago that I was loosing 70-100M per tack (land, turn then get flying again) to our pace setter who sailed the whole race "dry". That translated to ~1/4 - 1/3 of a windward leg each lap. You then change your tactical thinking that it is better to minimise the loss and say, sail on a knock and loose 30 instead if tacking and loosing 80.
In the moth fleet, (outside the top 20%) your tacking ability is the main factor in your finishing position in most races. We are only doing 15-18 knots upwind, the AC boats last time out in low mode were doing 24s so the gain will be much bigger for them.
When you compare a "touch and go" tack to a fully flying one, the difference is much smaller, but still very obvious.