[RichH]

Oil changes the surface tension of the water. This benefit retards the tendancy of a wave to become unstable and ''break'' (the top falling off and cascading in front of the wave). Its the breaking wave that does the damage to boats/ships .... the broken wave is full of air/foam, thus the boat sinks deeper into the water (water/air mixture) as it receives more ''side forces'' from the on rushing (higher velocity) water. A solid non-breaking wave will allow the boat to stay on top of the water, etc. so that the side forces that can cause the boat to roll over, etc. are minimized. A non breaking wave only has ''recirculating'' velocities - the wave moves but the water doesnt. A breaking wave can have large horizontal velocities (hence, forces), the larger the ''speed'' of water the larger the force.