My NP 1990 harness buckle broke yesterday so need to repair it. Maybe even get a new seat.
The typical harness for raceboard windsurfing, is characterized by having a very low hook position. This helps you to take the weight off your feet / board and put the pressure down through the mast foot. This helps the board to rail up in lower wind strengths. Some like the hook to be sliding from side to side, this makes it possible to take a forward rotated position with the body. Loft sails, Tunafish sportswear, Ion, Dakine and Boardwise are some manufacturers which produce a seat harness appropriate for raceboard windsurfing.These photos of top sailors illustrates why seat harness is good for race boarding since you can get on the rail, in the straps , leg extension and arms straight sheeting in and create upwind lift to go to windward. No way could you do this with a waist harness, at least, in my opinion, if you did you would put your back and body through hell. These photos were given to me by a friend and are not, naturally of me. Hope this aids understanding from a recent seat convert.