I read an article in Boards or Windsurf mag the other day about calculating the correct fin size for a sail..

for <110L: (sail size x 5) + 2
for >110L: (sail size x 5) + 4

The spec for my recently acquired Starboard Kombat(06) is 4.5m-6.5m sails and 22-33cm fins and it came with 25cm and 31cm. The above calculation would imply a 35cm fin for a 6.5m sail but as the fin box is the US style I haven't found anybody that sells fins above 33cm; most don't even go above 31cm.

So any thoughts on matching fin and sail size, on using fins of this size with a US box (not the most robust style), or on where to get fins in the 30cm range?

Also anybody know why Starboard use US boxes on a board of this size; I would have prefered Powerbox as all my other fins are this type.

My kombat is a 105 and I sail a 32cm with a 7m without a drama so I would be surprised if you would need a fin larger than what you have for a 6.5. My board came with 26cm which is good for 6.0 and less.