Over the past couple of years with the introduction of multi fin wave boards (mostly referring to quads and thrusters here) one thing that I have found pretty frustrating is how ridiculously over finned they are. The production boards are supplied with fins that are massive. They work ok in rubbish onshore jumping conditions, where early planing and upwind ability is a priority but in down the line conditions these fins really hamper the turning ability and loose feel of what are otherwise excellent shapes.


I personally use JP quads which are supplied with 10cm side fins + rear fins that are the same size as what I would use as a twin. Fanatics etc. all have similar sized fin setups. There is simply too much fin area. Changing down to 9cm sides with 13cm rears (the smallest JP make) it improved the board's turning especially in small waves where it felt a bit too stiff. The difference was promising. Others who have tried using smaller fins in their quads have all found the same thing - the waveriding ability is increased substantially with little loss in all round performance. However my verdict still remained the same - quads felt stiff in small waves from head high and smaller. The G10 fins provided little flex and were not forgiving through the turns, something that is needed when you have little time between bottom and top turning (ie. Small waves).



When I heard about K4 fins I was interested - flexy fins made out of plastic supposedly improving your boards turning ability with the added benefits of being substantially lighter and cheaper than G10 - but I wasn't entirely convinced. They could be too soft and spongy, losing out on speed, early planing and upwind performance. After getting my hands on some in 12, 13, 14cms and 6, 8cm side fins I have now got them out in some decent conditions and say that none of those concerns were justified. At first glance the fins were a pretty standard shape with slightly more area compared to the JP's of the same length. However the difference between the stiff G10 and flexy K4s was massive. My session on the fins was in gusty 15-25 knots cross off with logo high sets, testing the 8cm and 13cm combo. After two or three waves I was absolutely blown away at the difference the K4s made.


The first difference is noticeable as you come through your bottom turn. The flex in the fins is very apparent and as you are finishing the turn the flex 'whips' you out of the turn with an extra burst of speed that you do not get with G10. Suddenly you have more speed racing back up the face for the top turn - where the flex is the most beneficial. The K4's give control, speed and manoeuvrability through the top turn, allowing the board to rip around on the rail into full on roundhouse gouges or to push hard and chuck buckets with little chance of sliding out uncontrollably. The flex also helps when you are late hitting a section allowing you to go vertical and then come down with the lip in control. In these situations G10 fins can often spin out when the force of the wave smacks you back down into the flats. The K4s absorb the energy of the wave and allow you to sail out of turns you probably wouldn't have made with stiffer fins.

When sailing in a straight line fully powered the fins provide a pretty interesting sensation. It feels like the flex in the fins provides lift and the board feels like it hovers slightly higher out of the water than with stock G10. I found that this means you can load up the fins and crank upwind, they can slide out occasionally but it definitely feels different to G10, recovering easier.

Using the K4's so far I have only found one real downside - in choppy onshore conditions when backside waveriding is a priority, the flex can be too much. However these fins are not designed for these conditions and going up a bit in fin size overcomes this issue. Apart from that I've found these fins offer a whole lot of benefits for wavesailing, especially in down the line, clean waves.
I'm sure these fins do have limits - at a certain size the flex will become too much so they are only appropriate for multi fin boards using small fins under 17cm or so. Heavy weights may also find them too flexy for their weight in the larger sized fins that they would typically use but I believe K4 is about to release some stiffer fins to address this anyway.

For those with quads I would definitely suggest giving them a go. For those with hugely over finned thrusters (such as the JP - supplied centre fin is easily big enough to use as a single without 2x 10cm side fins) it would be worth experimenting with smaller fins all of a similar size eg. 16cm rear and 13cm front. I haven't personally tried it but have heard good things about improving the down the line performance of thrusters.


Summary:

Good:
Lighter than G10
Cheaper than G10
Better range and control due to flex.
More grip, speed and manoeuvrability on the wave in down the line conditions.

Bad:
Possibly limited to smaller sizes so only suitable for multi fin setups.
Loses drive with the flex through backside bottom turns in onshore.
Some heavy weights may find them too flexible.

Trying the 6cm and 13cm combo in tiny crappy waves today.




Hopefully some more action later in the week...