I just bought a 2011 starboard quad 87 L 59.5 W. to compliment my 2010 sb quad 76L
The 87 will be used with a 5.7 sail in the North Sea.
priorities: planing early, upwind ability and decent turning
my 76 has 15 cm front fins and 12 cm back fins.
the 87 has 11 cm front fins and 14 cm back fins.
What would be the biggest fin configuration I could use on the 87 for a 5.7 sail? biggest fins in the front or in the back? Considering the cost I would like to buy k4 fins. but I am confused by the different k4 models. I can't mix fins from the 87 with the 76 due to different box systems.
That is a lot of fin area on the 76 liter one! It came with 11 and 13 cm fins, while the 87 came with 11 and 14cm fins, as far as I know.
From 2011 and onwards they are all slotboxes so one can easily change between front and back fins.
From K4 I like the incinerator ones, they also come with an assymetric foil and toe-in in steps of 0.5 degrees. Another good choice is the Ezzy assymetric ones. On my 77 liter (2011) I have played around with the toe-in and I've use 2 degrees on the back fins and 3 degrees on the front fins. I've been using 10 in the front and 13 in the back, mostly, and that covers sails from 3.7 to 4.7 well. For the 87 and 5.7 I'm not sure, going to 16 cm would be the same as what they supplied it with in twin mode (!), if you have those (the stock ones) you could give that a go with some smallish front fins, I guess.
Or perhaps just run it in twin mode, that works a little better when using sails in the upper range of the board.
I tried both, the 2010 has more drive the 2011 more control. You can go 16 and 8 for a more conventional quad config. For 15.5 and 9. Look at what select recommends. As a twin 2x17cm.
I like the K4 Leon for a bigger fin. Very fast and slidey.
Haven't tried the Incinerator, didn't like the Skorcher for twin or quad.