So explain what the rocker line is?
Put your board down flat on a table and you'll see that the ends are lifted up higher than the middle. That curve the board follows is the rocker line.
Whats so good about rocker then?
Adding rocker to a kite board has several practical effects that you can easily feel on the water by swapping
between a board with high rocker, where the tips lift a lot and a board with low rocker which is flatter. The board with higher rocker will be smoother over the chop and on landings from jumps, the board will carve much better, spray you in the face less, the nose will trip less, it will hold an edge better and pop higher as a result. Great!
Nobile 50/Fifty Wake Edition - Wide with lots of rocker!
So more rocker is better right?
Not always, the downside of increased rocker is that the board becomes slower and less efficient and needs either more power from the kite or to have a bigger area. This is why kiteboards and wakeboards aren't quite the same. Wakeboards generally have LOTS of rocker compared to most kiteboards, which is fine because they have masses of power from a boat or a cable to pull them along. Kiters on the other hand are wind powered and unless they like long walks, need to stay upwind during a session. Staying upwind needs an efficient, flatter, faster board, as the kite needs to be right at the edge of the window to go upwind, where it makes least power, not good if you have a slow power hungry board with high rocker.
So I need a compromise?
Yes, and most modern kite boards have become very effective at delivering a mix of good planing with reasonable control. There are a few different ways this can be achieved by the kite companies. Firstly you can ride a high rocker board in a bigger size. More area gives you better planing and you overcome some of the inefficiency. This is a good choice for wakestyle kiters as the bigger board allows for a wider stance and gives a larger more stable platform to land fast powered tricks on.
Nobile T5 Freeride has lower rocker and concave in the middle.
But I want to freeride in choppy water...
No worries, the other way to achieve the benefits rocker without the downsides for the majority of kiters, is in the shaping of the rocker line and the base of the board itself. If you look at different rocker lines they aren't all the same. A continuous rocker is a simple smooth curve created by a single radius. It looks great & rides nicely but isn't terribly efficient, so to counter this companies like Shinn and Nobile have combined the rocker with a concave through the center of a board like the Monk or the T5 (shown here). So now the board is effectively flatter in the middle for efficiency, but still has its rocker on the rails to keep the handling in chop and under load. Another way to overcome the drag is to lower the rocker slightly in different areas to change the way the board rides whilst maintaining the benefits of having an amount of overall rocker.
Does a boards stiffness affect the rocker?
Yes, this is called dynamic rocker. If you put a heavy powerful rider on a board which should be the right size for them, but which is much too soft, it will feel slow and difficult to get up wind on. This is because they are flexing the board and effectively putting more rocker into the board as they ride.
There are loads of factors which affect the 'feel' of a kite board. The best method of choosing is always to get as many demos as possible and look at the shapes of what you are trying, to gain an understanding of what works best for you.