how does movng the mast base back or forward affect sailing and can it make easer to get planing

from my experience (have heard the opposite before..)

forward - flatter board trim from more weight forward so earlier planing
aft - less board in the water - better control in high winds

can also be moved forward the bigger sail you are using to balance the centre of effort, although don't see this makes a huge difference

have a play with it.. right to to the front then right to the back see if you notice a difference or just put it in the middle and go sailing!!

Al

As a rule of thumb:

mast base further forward = more board control

mast base further backward = better speed

HOWEVER, most boards these days have a middle position marked on the mast track. The shaper / manufacturer recommends you play with positions before and behind that middle marker as it's not an exact science and performance is also influenced by variables such as your body weight, body height, stance (foot strap width) and preferred riding style (flat water, wave, bump and jump).

I have played with this a bit lately and it makes a huge difference to how comfortable and how balanced your set up is. 1 cm makes a big difference.
Back improves your top end speed but may make it more difficult to force the nose of the board away for beach starting/ waterstarting, or down for high wind handling, so it's a compromise.
Choose a point to start with (middle?) and then move the base 1cm, sail, move 1 cm, sail, until you find the optimum balance of comfort and speed. Optimum will change if the wind strength changes.

whats best base ( forward or back ) position for getting upwind, or is it all technique, all tips will be appreciated.

would personally say forward for upwind but that might be because on wave/freestyle boards you want more rail in the water and weight forward. not sure if this is the same for slalom.