How does surfing relate to Zen?
In Zen Buddhism, you train all your life to master what nothing is all about, once you attained the ability to understand this, that opens up a door to completely new potentials. This manifest in many aspects of surfing, but one of them is to make yourself totally balanced. You add nor subtract the balance, essentially becoming a "nothing" on the board. Whether you are paddling out, or standing up, you and your board are perfectly centered each other of respective small universes. Once you attain this nothingness without being trapped in other issues, then you and your board become one, then with just a simple shift of your weight you can make your board do what you want. I think this would be hard but something to keep in mind as you attain a higher level of surfing. I have not mastered this.
Another part of surfing is overcoming your own fears. The first time out, a hip or chest-high white water tumbling you and your board may cause you to become very afraid of making you imagine should this have been bigger you'd been killed. A little while later you overcome that, then these white water waves mean nothing to you. So what has happened? You have became much stronger to deal with it? I think that it is mostly your mind now being confident and know that you can handle the stuff. But then you challenge the next bigger set, you once again become smashed and you are now afraid again. A bit later on you know how to deal with it. So some (and I think a good deal of) part of this sport is about overcoming your own fear, something just in your minds, and gaining the control of it. I am not saying that you should never be afraid of anything, in fact you should rationally act and work with dangers, and through mastering this skill, you can also use this to your other life situations, such as work or relationship with others.
A great part of the fun of surfing is to one day you realize you are in the middle of and became a part of the nature. You have taken off your cell phone, a watch, a Palm pilot leaving the year around comfort of air conditioned room. You are now directly dealing with our own Universe (tides caused by the position of the moon, sun rise, sun set, the wind), and our nature letting you share the playgrounds of seals, dolphins, pelicans... As you now realize that you are no longer in control of the nature around you, you are enlightened by letting the nature allowing you to become a part of it without a fear.