If the suction on the windward side of the fin is becoming too big, vapour bubbles will be produced and the flow will break down. The consequence is a sudden loss of control. Modern fins and boards have succeeded in reducing this phenomenon. A good fin will mostly signal the approaching spin-out to the experienced sailor thus, he can take the pressure off the rear end of the board and pull it closer to his body.

Some factors that are increasing the risk of spin-out are:

• high sailing speed
• thin profile
• slow responsiveness
• too big angle of attack
• too much pressure on the rear end of the board
• ventilation of the fin caused by turbulent water, crossing of a wave, after a jump, badly constructed underwater side of the board
• fin is too close to the rear edge of the board, air will be sucked in
• fin design and twist-flex properties are not in harmony, fin is extremely stiff or extremely soft