WE RECOMMEND THAT WHEN FIRST USING K4FINS YOU PLACE THE REAR FINS SLIGHTLY FURTHER BACK IN THE BOARD THAN YOUR OLD FINS.
As with many things in windsurfing, fin tuning ultimately comes down to your own personal preference, your board and the conditions you sail in. There is NO one right set up. With that in mind, here are our guidelines and some general rules..
As virtually everybody has used g10 fins in the past, the simplest size guide is to compare K4fins with a similer template g10 fin.
For an average weight sailor (75kg, 165lb, 12 stone), the fin size used would be the same. K4fins will provide slightly less bottom end drive for early planing, but provide more grip and drive in turns due to their flex properties. K4fins will also feel looser for a given size and more controllable in windy/choppy conditions.
The lighter you are and the more fins your board has the more flex your fins should have. If we imagine both ends of the scale; a 55kg sailor sailing on a large quad board in good waves with a 4.5m sail in light winds, and a 95kg sailor sailing a 6m sail overpowered in chop on a small single fin board (or rear biased Tri fin), the difference in fin force is huge. The lighter sailor will need very flexible fins in order to get the most from his board and the heavy weight stiff fins to deal with the high loads. The more fins you have in your board the more the load is shared and the less force on each individual fin. Obviously the higher the load on a fin and the longer the fin, the more it will flex. Our shorter fins are designed to have more flex than the larger sizes.
For the heavyweight riders of 90Kg plus we have brought out a range of stiffer fins, called the STUBBY. Although we have many 90kg+ riders who love our FLEX fins, we realise that for use in gutless waves, chop and/or overpowered conditions some extra stiffness would be a good thing particularly with rear biased set-ups.
We've found that for Tri fin set ups in good waves, almost equal sized fins are best with K4fins (eg 13 sides and a 14 or 15 rear). This will help all the fins work together and give a 'quad' like feel, maximising looseness and turning ability. Any of our front fins can be used; the CARVE have more base area and sweep, giving better control and drive, the SHARK TOOTH fins will be looser and faster, and the STUBBY's will give more pivot and a direct feel.
With Quad fin set ups you can tune your board to feel more 'twin' like with smaller fronts and larger rears (eg 6 or 8 fronts and 15 rear), a standard quad (eg 10 front and 14 rear) or even go with bigger fronts and smaller rears (13MT tri or 14 US rears in the front and 12 rears).
A rear area bias will make your board feel looser, easier to redirect or change line mid turn and have better 'pivot' in your top turn. It will be more 'twin' like in feel and we would recommend this set up for onshore conditions where looseness and snappy turns are the main requirement.
A standard quad set up will make the board feel drivier in the turns, much better for swooping cutbacks or power gouges. More grip and confidence in hollow or steep waves. The trade off is slightly more difficulty in changing your line once set, and top turns may feel less snappy.
A front area bias will make the board easier to 'push' through turns and release the tail particularly when underpowered. You may find you lack speed and drive down the line with this set up though, so it's better suited to slow softer waves. You can get some nice 'hooky' top turns using the rail with this set up and can be good if you're not having to chase the critical section.
The following is true for any fins and will help you get the best from your board..
Moving the fin cluster (1,2,3 or 4 fin) rearward will give your board more speed, more grip and more control. Better for big waves or big wind and perhaps for onshore conditions where drive and upwind are important.
Moving the fin cluster forward will make your board looser and skatier. Better for fun size waves and rippable conditions when nicely powered up.
Moving the fin cluster apart (tri and quads) will make the board feel more planted and stiffer. Better for large waves.
Moving the fin cluster together will make the board looser and with more pivot. Better for small waves.
The outline of your fin makes a considerable difference to it's performance..
A wider base will give better drive and acceleration.
A narrower base more speed and pivot.
A more upright fin with less 'sweep' will give tighter turns and more pivot.
A more swept back fin will give better control and more sweeping wide arc turns.
More area will give more hold but be stiffer for a given length.
Fins with a longer tip out the back (or rake) will give more grip and direction, better for larger arcs and powerful carves.
Fins with less tip will be more snappy and turn tighter, better for staying in the critical section of small waves.
For many years all surfboards have been supplied with asymmetric front fins, windsurfing has only just caught on, perhaps in some part due to the extra complication for manufacturers and customers (I'll make this as painless as possible!).
By creating an asymmetric foil you can increase the amount of lift generated whilst keeping the drag low, the same as an aircraft wing. Asymmetric foils are more efficient at creating lift. This means more drive, power, hold and grip when your board is turning without a drag penalty.
Where things become complicated, is that an asymmetric foil will create lift when running 'straight', ie. it will pull to one side. This 'pull' is undesired for several reasons, but mostly that it is causing drag. In order to prevent this we turn the fin in towards the nose of the board until the fin neither pulls one way nor the other. This angle is the 'toe in'. Of course the amount of 'toe in' for no lift (least drag) in a straight line varies depending on board design and how fast you're travelling!
Most boards will perform best when the toe angle is between 2 and 3 degrees. The k4s come with a choice of +1 or +2 degrees added toe. Therefore a board which has straight boxes (zero toe) will need the +2 fins, and a board with 1 degree or more boxes will need the +1.
You can also tune your board with toe in to some degree; small wave surfboards can have over 3 degrees toe, this is to make turns easier and sharper and can do this as the top speed is less important. Big wave surfboards have less toe for more drive, higher speeds and wider turns.
To keep your K4fins looking clean and shiny it does them no harm at all to go in the dish washer every now and then. This is highly recommended.
Minor nicks and scrapes can be easily sanded out with 240 or 400 wet and dry.
Major damage can be trimmed or scraped smooth with a sharp knife.