Fun Design! It's a really good variation between the others out there.

I'd go for the tattoo myself. It's a great way to mark this part of your life and -t-shirts wear out.

One thing to keep in mind though is that if you are going to get it tattooed on is that where the waves over lap the gear the artist probably wont be able to overlay the blue on top of the black. I still think the design would work well with the waves being solid though.

I'm getting the top to my triathlon/marathon back piece done the end of this month. I'll be sure to post pictures of my design then.