Flexy fins - K4 fins review

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...

Well yes and no... I do think most production quads are over finned - JP, Fanatic, Starboard etc.
Have heard good things about the MFCs that come with the Goyas and Quatros.
These fins aren't just about using smaller sizes - they are a completely different feeling to G10.

Yeah the wind ended up being suprisingly good - would of been nice if there was a bit more swell.
What size fins have you got at the moment? If you want you can try a spare set next time I'm down at the island to see what you think.

I have the standard setup that came with the quad 2010 - 15/10.
That would be good to have a go. Or let me know when SHQ has them in.

When I ground the plastic ones into a rock (not the ones I demo of course) I might not feel as bad. Quads are still as new but not much left of the Stone thruster.

Totally agree!
I had the same thoughts on the quad

Ended up getting a small set of MFC quads and it made the world of difference.
It's just the front fins that needs to be smaller...

Why do boards come out standard with such big fins? I think mainly because of magazine testing.. they need them to go upwind!!

So based on you learnings what sizes should i get to try in my new 74 quad i have waiting for me when i get back to Perth. 9 and 13??

I had great success with the stock fins on the 2010 JP quads with the back fins forward and the front fins back.
I did find with the JP 2011 75L thruster i had to drop down to a 17cm main fin with the stock side fins. I tried other side fins but the stock ones worked fine.

Well I dunno about the above...im a shade over 90kgs and think they are awesome fins. Massive difference...
I will only put them on once im able to rig my 5.2 (25kts) and lower and love them, you can turn so tightly and get everything out of a wave.
20kts or under - on my 5.8, I use the stock MFC fins on my quatro quad 85 (which are pretty good too).
I would recommend for the heavier sailor once the wind is up. Buy them NOOOOW!

@ Phil,
The main diff is that you ride a quad and I a trifin. 13 in the front and 15-17 in the back is something diff as 10-13
So maybe i didnt wrote it correctly, I meant that wouldnt recc for a Trifin at people of 90kg.
The bigger fins are too flexy for me and made me spinning out way to often.
I blaim just the lack of stiffness as I really like the profile and wint spin with my Muffins with a way smaller surface.
Right now I use the backfins under my SUP and like them there a lot and hope the stiffies will be released soon.

Yeah man thats cool, was kinda thinking you may have meant that but I got a bit excited and typed away!...Cos those fins.. are just so DaMn GoOd! yer

I find them OK up to 13, 15 too soft. I'd recommend you to try them in front on a tri but keep a stiff G10 centre fin.

Cheers! -Doc.

On the subject of quad fins: I've ben doing so much fin testing this year, and board testing too for that matter, that I haven't really concentrated on my own sailing. We developed three lineups of quad fins. Now when things are calming down a bit, I have retrospectively thought about my sailing this year and I'm not really that satisfied. But lately I went back to my "old trusted" quad setup with large front fins and small rear fins (125-140 fronts and 100-120 rear) and it is crystal clear that this makes me sail so much better. And I know from friends that it works very well for other too. I think a reason this setup is not more popular has to do with lack of toe in and also that some put's their front fin boxes a bit to far forward for a front fin oriented quad to work. Also most people were still sort of blown away with the twin fin type of ride when the quads came around. I like that too sometimes, but in my opinion it is still just one (extreme) end of the possible performance spectrum of a quad board.

We will not make the big front/small back setup standard in the Simmer boards (but our Black Tip line of quad fins are designed to work in this setup), but I personally decided to focus on it for my own sailing, both for small waves and onshore and for big clean sideshore stuff. You can use much more fin area overall with remarkable combinations of drive/grip and looseness. You only need to be bit more "on it" since you're gonna carry more speed through a tighter arc than with a "twinzer style" quad setup. But with the right toe in and the right fin design it's still rather forgiving.

I'm waiting for some K4 fins myself and will see how they work on both the type of setup mentioned above and in a regular setup. Even though we have our own Simmer line of fins, I think the K4s are a great idea since they seem to combine good performance with a low price which makes testing around a bit much cheaper. My take on the whole fin issue is that on any given boards, there is HUGE amount of tuning you can do to set the board up as you like it. I think we have only seen very, very little of what the quad concept can offer.

Nothing wrong with a good old single fin, but the conditions you describe would be perfect for a quad with a big front fin and small rear fins (assuming the front boxes are set up right and the front fins are preferable rather flexy). Basically, both in the bottom turn and top turn, if you sort of keep some rail engaged and drive the board forwards, you will have an immense amount of fin drive. But the second you release the forward drive, it is like the big front fin no longer is in command and only act as a pivot point. So you can whip the board around super quick. Twist it around sort of. Very surfy. But again by keeping the board more on its rail you can also come out of the top turn with heaps of speed. So what I like about the setup is that it is so versatile and reacts so well to different sorts of rider input.

When I tune this sort of setup, the size of the front fins (I use between 125 and 140mm) pretty much only determines the amount of grip without really affecting looseness or drive that much. The size of the rear fins increase drive but at the prize of slower reactions when altering the turning radius. I use between 100 and 120mm. Moving the rear fins forward will give you more looseness so if you're worked about upwind and planing and want a more "traditional" feel in a straightline, you can use bigger rear fins mounted a bit further forward. The price is a bit more drag though, but if can be a good setup for onshore.

Tried the new "stubby" template K4 fins yesterday. I used vario MT 12cm fronts and 14cm rears in my 64,5 quad. It's flat with moderate vee, not much concave, so a lot of pressure on the fins, especially when trying to stay upwind in onshore conditions.
I don't have 14 MT or I would have tried that, too. 14MT + 12US might be really sweet!

Impressions? Nailed it on this one! Where I've previously had trouble with too much flex in the rear fins in gusty conditions now the board felt secure. None of that sideways riding feeling I've experienced. There's still a nice flex and I don't think they're too stiff.

I believe I'll keep using the flexy template for large (13) fronts and on my smaller board, and use the stubbys for the wide board and onshore sailing.
Also, heavier sailors will love this template I think. Or those who for whatever reason prefer stiffer fins. (Still not like a stiff G10 of course).

Ed, Im 78kgs and have been using K4 14s in the back and 10s in the front on my fanatic 79 quad for a few months now and they seem pretty good.