This...but the ice "cube" has a slight taper to it, like a wedge. As you might recall from high school or freshman Physics, a slight-taper wedge has a large "mechanical advantage". By squeezing it, you use that in reverse - a slow-but-strong push from your fingers (the wind vs. the keel+rudder) results in a fast-but-weak movement of the ice "cube". (Hence the ultra-streamlined shape of the vehicle, low-rolling-resistance tires, etc.)