The additional people on the rail also adds considerable weight to the  total 
weight of the boat. Placing 300 pounds of weight on the rail in relation  to 
the total weight of the boat allows me to point higher and keep more wind in  
the sails, thus more speed. Without the weight on the rail, I am not able to  
point as high, nor keep as much wind in the sails. Hope this helps. This may 
not  be a scientific explanation, but it's my observations from years of 
sailing this  boat.
 
Rummy