What would happen if you covered a swimmer with a hydrophobic substance?

We put Luke's question to chemist Ben Pilgrim... Ben - Firstly I'll just recap what a hydrophobic substance is. Hydro obviously refers to water, phobic means dislike, so a hydrophobic substance is something that doesn't like water such as oil which won't mix with water and will sit on the surface of water. If we think about trying to move quickly through water, the main thing that stops that is drag. That's the problem moving through any fluid at speed; it's how quickly you make your way through the fluid and this is actually is a very interesting question. If you think back a few years ago you might have seen a number of swimmers wearing these full body suits which were subsequently banned.

Chris - They were called the sharkskin suit, weren't they?

Ben - And these suits did a number of things. One they sort of smoothed off the body to reduce little holes and things like that which might cause turbulence in the flow, but they also were coated in certain sorts of substances that trapped small amounts of air near to the surface and meant the water flowed over the swimmer much more quickly.

Chris - Did they work?

Ben - Did they work. Yes, they were reckoned to produce about a 2% increase in speed and a lot of world records were broken. However, this was then deemed that this was slightly unfair and so they were subsequently banned and limited in size. So to go back to the question, the main thing with going fast is drag. If you can have a hydrophobic substance that repels water, this can make a small increase, but the main thing is just to do with the shape at which the body is that moves through water.

Chris - And so, therefore, if you streamline your body but then you add something that repels water from your skin, it stops the water sticking to your skin so much, so you should go a bit faster.