DN NA Class

                                       WHY ICEBOATS SAIL SO FAST ( I THINK)

     Several of us were out sailing on my boat one day and we tried to figure out why  iceboats sail faster then the wind and here’s what we came up with. When going to windward as the wind passes over a sail it creates an aerodynamic force that drives the boat forward. As the boat starts to move forward it creates a relative wind which increases as the boat gathers speed. When a soft water boats gets to it’s maximum speed , if you have wind instruments on the boat , you will see a relative wind speed that is greater then the true wind speed . Relative wind is the vector sum of  true wind speed and  boat speed and is the actual wind the sail sees. As previously noted, as a boats  speed increases so does the relative wind speed which creates an increase in the driving force which in turn makes the boat go faster which again increases the relative wind speed. This cascading effect continues until the driving force on the sail is equal to the  drag  and friction forces on the boat. In the case of a soft water boat it’s typically in the 4-8 kt. range. This is because of the huge amount of drag  water creates on the hull. On an iceboat there is very little drag and friction. This allows the boats speed to exceed the true wind speed. That’s our theory and we’re sticking to it.

         Friction and drag are an iceboats enemy. On a one mile, three lap race  in moderate winds, a boat that is one MPH slower both upwind and downwind then another boar  will be about ¼  mile behind the other boat at the finish. Small changes can mean a lot. We can decrease friction by properly sharpening runners and getting the best runner alignment possible. The best way to minimize drag is to keep your body down in the cockpit.

   

                                                          Bob Gray, US 4654