Apart from the obvious interests :
What equipment we use for sports, what clothes we wear, what we like to eat and drink...
I imagine it would be of interest to potential sponsors to know what sort of work windsurfers generally do as well.
Other things windusrfers like would be of interest and may point to some opportunities:
Windsurfers like speed, adrenaline, challenge....
Persistent bunch. Learning their skill for some years.
All ages (and mostly old

)...
What else?
Compete with themselves, and against everyone else, and yet, friendly and helpful.
Like bad weather...
People who buy vans...