Make a viper weigh 107kg and it WILL be faster than the std boat.
What do you mean by "standard boat"? This is a formula class. As far as the Viper itself, the designer/builder says that if it were 18 kg lighter, it would be faster by only 30 seconds per hour.
In a big fleet regatta an extra 18 kg will set you back 30 seconds, possibly more on each downwind leg alone. More so if your crew weight is not down to optimum weight. You will be forced to run hotter angles then the lighter boats and they will just suck down inside you (if they are behind you) and gybe well in front of you. The boats in front will just stretch their lead further..... Hence it will cost you many positions..... Forget time. 30 seconds can be turned into 2 min 30 seconds over the course of a race within a big fleet as each boat passes you and feeding you gas.
I have raced my F18 carrying an extra 18kg of crew weight onboard and watched this happen many times. Then when I am sailing at min weight, the disadvantage is gone and you are doing likewise to the heavier boats.
Upwind also, the heavy boat will not accelerate off the line like the lighter boats (The most important part of the race) and it will not be able to sail with as much height or speed.
