You know how sails 'breathe' and twist off to keep control and deliver speed? K4 Fins do the same to multi-fin wave boards by designing a flex pattern that works with you. K4 Fins have created a unique and new material for windsurfing - OptoFlex is a molded resin long fibre matrix that has been carefully manipulated to provide the perfect flex patterns for windsurfing. K4 technicians took a long time to create the perfect material with the qualities needed to provide the performance. K4Fins are moulded using a plastic composite material giving them the correct flex and strength properties - similar to surfing's 'Glass Flex' FCS fins and 'Natural Composite' Future fins. They use the latest materials and processes as recommended composite experts and have been testing the highest grade materials in the lab and on the water for nearly two years, continually improving the aesthetics and the performance.
I have been extensively testing K-4 twin fins (17-16-15cm) in NZ for 6 months everywhere from Pungarehu, Kina Rd, Waitara, The Ditch, Takapuna, Orewa, Managawhai Heads, Omaha, Auckland harbour - and the fins have delivered in all conditions from nasty choppy 'egg-box' sea states, to cross-onshore mushy waves and to prefect cross-off logo high DTL reef breaks. They rip and I cant see my use my G10 fins again in a hurry! Even though they seem so soft they don't spin out even in the harshest sea state and when totally overpowered!
The K-4 fins work awesome on the wave face. Sooooo much more traction and torque off the bottom and top turns. You can feel the fins flex with the carve when really loaded up off the bottom turn but through the last quarter of the turn they then whip the board around and provide a extra squirt of acceleration to drive you back up the wave face more vertically than ever before!
The top turn on the K4 fins is something else. You can crank as hard as you like and they engage traction like a 4WD off the top and keep turning. You can feel the fins loading up and flexing but you get whipped around so fast and can 'round house' the cut back super hard into the breaking section, or do those new school super whippy cut backs. Also I have been doing the best and longest lip slides ever as the fins release easily off the top to initiate the slide but they come back in again just as easily to control the end of the slide and let you sail off feeling like a rock star!
Simply, the more energy you put into the initiation of a bottom/top turn the more performance the fins will then deliver back to you! The fins release the energy you put in at the exit of the turn in the form of a squirt of acceleration right where you want it!
Also in cross-onshore mush when going front side the fins will load up but then release off the top turn far easier than G10 which makes tricky front side riding easier in onshore winds.
I have used them in Taranaki, NZ, quite a bit, which is rocky...like really really rocky and have had no issues with robustness. I have scraped them a few times but as the fin material is soft I have simply used my finger nail to tidy up the scrape and later on use a bit of light sand paper to take the roughness off. I reckon that hitting a rock with a K-4 fin you are likely to dent the fin versus smashing a thin foiled G10 fin to pieces!
Basically, I am doing turns I've never done before on my Mistral 84 twin fin and I have sailed that board a lot prior to swapping to K-4 fins so I know what the difference is!
Check out this link to the Boardseeker.com review of K-4 Fins: " K4 fins provide very good grip with a really nice balance between drive and looseness off the top. They will make your board livelier, yet more controllable. Theyre perfect for any wavesailor whos focused on waveriding, and the pricing is as impressive as the performance."
Graham Ezzy on riding K4 Fins @ Jaws: "Last week on Maui the swell was lining up to be massive enough for Jaws to break. I was excited for the big waves but also a bit worried because the only fins I had were my new sets of K4 plastic fins. And while I loved the fins in smaller waves, I wasn't sure whether they would be too flexible for the big bottom turns at Jaws. Without too much thought, I threw in a pair of 15" back fins and 7" front fins on my quad board. I was the first windsurfer to ride a quad board at Jaws back in 2009, and last week I think I was the first windsurfer to ride plastic fins there. The best part was that the fins worked amazingly. I was able to push really hard in the bottom turns without anything close to a spinout. And I was even able to throw a big air. It was the first time K4 fins were used at Jaws but it most definitely won't be the last!"