For many years all surfboards have been supplied with asymmetric front fins, windsurfing has only just caught on, perhaps in some part due to the extra complication for manufacturers and customers (I’ll make this as painless as possible!).
By creating an asymmetric foil you can increase the amount of lift generated whilst keeping the drag low, the same as an aircraft wing. Asymmetric foils are more efficient at creating lift. This means more drive, power, hold and grip when your board is turning without a drag penalty.
Where things become complicated, is that an asymmetric foil will create lift when running ‘straight’, ie. it will pull to one side. This ‘pull’ is undesired for several reasons, but mostly that it is causing drag. In order to prevent this we turn the fin in towards the nose of the board until the fin neither pulls one way nor the other. This angle is the ‘toe in’. Of course the amount of ‘toe in’ for no lift (least drag) in a straight line varies depending on board design and how fast you’re travelling!
Most boards will perform best when the toe angle is between 2 and 3 degrees. The k4s come with a choice of +1 or +2 degrees added toe. Therefore a board which has straight boxes (zero toe) will need the +2 fins, and a board with 1 degree or more boxes will need the +1.
You can also tune your board with toe in to some degree; small wave surfboards can have over 3 degrees toe, this is to make turns easier and sharper and can do this as the top speed is less important. Big wave surfboards have less toe for more drive, higher speeds and wider turns. You still need to stay within a reasonable range of toe though, so as not to cause unnecessary drag.
Simple guide to measuring your boards boxes ‘toe angle’ with this quick table…Difference in span between the ends of your front boxes in ‘mm’ and the angle of toe your boxes have (taking a 10cm box length)
DIFF 0 = TOE 0
DIFF 1.75 = TOE 0.5
DIFF 3.5 = TOE 1.0
DIFF 5.25 = TOE 1.5
DIFF 7.0 = TOE 2.0