[Pirate Rick]

the duct tape absorbs and "changes" the vibration frequency slighty which gives the board a smoother vibration range and less jumpy figures.

it can get really technical if you want to dive into the whole dynamics of it but the best way to understand it is to think of it this way.....

if you throw a rock into a pool of still water you get perfect ripples that radiate out from the place where the rock hit the water and they stay that way till the hit something...like the side of the pool then they start to bounce back and start to collide with each other making turbulance to the other ripples.

the vibration is the same way.... it starts out smooth but by the time it travels down the field it starts to collide with the other "waves" and makes the bouncy running you described.... the tape absorbs those rouge waves and allows the original vibrations to continue uninterupted down the field..

hope that helps.