Hey Guys, I was just reading some of the realy helpfull info here at the BB. Now correct me if Im wrong but the fin aspect of surfboards in recent years has sort of become a real marketing point. With new configurations and installation methods appearing every year. Ok heres a story about fins, its about a speed boat fin. Now the designer of the boat did a good job and the designer of the fin did as well. But when the boat started to reach its top end speed there were troubles big troubles as the craft start to bounce and yaw from side to side. And this problem they were having was stopping them from breaking a water speed record. So they called in a engineer. After studying the boat and the stabilising fin, he concluded that at the rate at which the boat would be going there would be so many tons of drag per inch of fin immersed in the water. In fact by removing 1" off the tip they released about 4 tons of drag at the crittical speed. So they broke the record and then in trying to break their own record they came against another problem. The hull flow forms were not designed for the next level of speed capable by removing the drag. How you can overcome this is another story. So the above is an extreme, but the moral of the story is more fin in the water more drag ! Ok one thing Ive noticed with installing any fin systems that use round dowls is that they are weakening the boards tails. The shape of the insert cut is round so where ever you bore into the board firstly you break the glass mattings nose to tail linear structural strength and secondly you provide a flex point for pressures to work on. When building FP I have to very aware of this as my boards go faster they are exposed to higher stesses, in fact when using installation kits I have to beef up the resin in the dowl because in the recommended technique my fins were simply breaking out of their dowls. More correctly the recommended fins were breaking then I made my own fins to fit the installation kit and thats when they started to rip out of the board. You may have seen one of my boards it has four fins and then you may say, well, more fins more drag. If you measure the front fins as compared to say a drive fin that I have removed the area is quite different. Smaller as you can guess. The act of removing the rear drive fin and replacing it with 2 small directional fins gave me a 8% increase is speed alone ! Now another thing I see in 99% of all fins is incorrect foiling ! The foil or wing chord, same thing, in 99% of all fins is halfway! This is incorrect. A halfway foil is relative to bird wings and plane wings. Aquatic foils are one third from the tip to the widest point not half way. Just a rave thanks guys ! http://www.geocities.com/wunderboyi/ninetysixpercent.html
I learned something new today>>>
your comment that you got an 8% speed increase implies two things: one, that you can measure this small increase, and two, that you can measure to within one percent (that your actual increase is somewhere between 7.5 and 8.5 percent). Pray tell, how do you or anyone else measure to this accuracy? Having worked in an oceanographic research lab I notice you didn’t mention a force balance, wind or wave tank.