The Uk Royal Yachting Association has offered guidance for boaters regarding Kitesurfers; they write that "The new sport of Kitesurfing is growing at a fast pace.
More and more boaters may come across kitesurfers and it is important to understand their unique characteristics with regards to requirements, speed, tack and manoeuvrability."
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Avoiding kitesurfers ? Guidance for RYA Water Users is a useful analysis of the the issues and offers some sound safety advice.