Hi Joerg, not sure if there is a scientific minimum, but we are selling quite a few 60cm masts for places like Neusiedlsee and similar spots in the Baltic/Lakes with lower water levels. Of course you can go shorter but then you have less time to react when the board is lifting off/touching down....so the shorter the mast, the more stable the foil needs to ride "flat", otherwise it will constantly go up and down...that is something that our foils do very well, height control/stability.