There has been some discussion about whether dimples have an effect on a surfboard. So I posed the question to mybrother who has his Masters from MIT in Mechanical Engineering. He posed the idea to his former professor. Here is the reply from a MIT professor,
"Dimples on a surf board is a non starter in my opinion.
For a golf ball, dimples reduce the drag by a massive 50%. This is because the drag coefficient is reduced by 50%. This is because for a smooth sphere, the separation point for the streamlines is just aft of the midpoint of the ball and as such, there is a massive low pressure aft side. Dimples on a golf ball move the separation point significantly backwards which causes the surface area exposed to the low pressure air to be dramatically reduced. This separation of the dividing streamline is associated with flow past bluff bodies.
A surfboard in not a bluff body. It is a streamlines body and as such, there is not a dividing streamline and thus not a low pressure side. For a streamlined shape like a surf board, the drag coefficient is very low to start with and there is very little form drag, which is what happens on bluff bodies. For a surfboard, 90% of the very little drag there is is due to surface friction. So to reduce drag, you reduce fouling and surface area.
You could play with changing the surface drag by using very small dimples or a shark skin shape, but you are really only going to see only a very small incremental change at the Reynolds number a surfboard operates.
See any undergraduates fluid mechanics text for discussion of bluff vs streamlined shapes and impact on drag. For dimpled vs smooth spheres, see http://www.efluids.com/efluids/bicycle/bicycle_pages/sportsballs.jsp
I am sure you could make some hay from a marketing perspective because the general public has been sensitized to the importance of dimples on golf balls, but from a purely technical perspective, I don't the incremental advantage would be worth the effort".
"Dimples on a surf board is a non starter in my opinion.
For a golf ball, dimples reduce the drag by a massive 50%. This is because the drag coefficient is reduced by 50%. This is because for a smooth sphere, the separation point for the streamlines is just aft of the midpoint of the ball and as such, there is a massive low pressure aft side. Dimples on a golf ball move the separation point significantly backwards which causes the surface area exposed to the low pressure air to be dramatically reduced. This separation of the dividing streamline is associated with flow past bluff bodies.
A surfboard in not a bluff body. It is a streamlines body and as such, there is not a dividing streamline and thus not a low pressure side. For a streamlined shape like a surf board, the drag coefficient is very low to start with and there is very little form drag, which is what happens on bluff bodies. For a surfboard, 90% of the very little drag there is is due to surface friction. So to reduce drag, you reduce fouling and surface area.
You could play with changing the surface drag by using very small dimples or a shark skin shape, but you are really only going to see only a very small incremental change at the Reynolds number a surfboard operates.
See any undergraduates fluid mechanics text for discussion of bluff vs streamlined shapes and impact on drag. For dimpled vs smooth spheres, see http://www.efluids.com/efluids/bicycle/bicycle_pages/sportsballs.jsp
I am sure you could make some hay from a marketing perspective because the general public has been sensitized to the importance of dimples on golf balls, but from a purely technical perspective, I don't the incremental advantage would be worth the effort".
