You are correct that those boats can break their daggerboards when fully extended with the boat fully powered up to windward in 20+ kts - the loads on a deep, high aspect foil in these conditions are very high. However, those are 9' boards, and the solution is to bring them up to 6'!

While this results in relatively more leeway, they are not accepting much absolute leeway with this concession - much less than almost every cruising boat of any type out there - I have sailed them in these conditions.

Mark