Reason for recommended sail ranges?
We are now surfing an old f2 slalom comet 315 and looking for a second board with about 115-125 liters for me and my children. I am an intermediate surfer, my children (age 15 and 9) are learning/beginners. Our sails range from 3.5 m2 to 7.0 m2 (3.5, 4.8, 6.0, 7.0).
When looking for possible boards I often find recommended sail ranges, often higher than my sails are (for example 5.5-8.5 m2). I would like to know the reason for these recommendations.
My little daughter has now on the comet 315 a problem with going upwinds with her small sail. I think the reason is just that the boom of this sail is too short even with the most rear position of the mast.
Will we have the same problem with a new board when the recommended sail range is only higher than 5.5 m2? Could a smaller fin really solve this problem?
Or is there no correlation between board length and shape and the sail range?