Conclusion
From the graph tell us many characteristic of
sailing boat 
1.) Starting from making 0 deg with wind direction to 135 deg with wind direction main-sheet position would be place starting from 90 deg then reduce to around 20 deg with boat.
2.) when boat in making less deg with wind the sensitivity of boat speed to main-sheet position is low and it will be higher as the deg of boat and wind increase.
3.) boat will go fastest around 115 deg with wind direction and sail boat can run faster than wind speed
4.)the max speed of boat starting from 0 deg with wind direction is never br more than wind speed and are not much difference untill boat and wind is 50 deg then max speed begin to increase to the fastest position around 115 deg then drop quite fast when the deg of wind and boat are greater
5.)ALL of this conclusion are base on one concept than the water resistence to sail boat in very low ( and it is true) if the resistance were great for example if you imagine that you sail on sirup the result will be differance this can be done by increase the R constance
- the result will be that the fastest direction to sail is 0 deg with windirection and the ship will never run faster than wind.