I bought a waterproof (50m) Prospirit watch from K-Mart for around $30. Stuck it on my boom as I hate wearing watches.
Now the time is always available if needed. I get some funny looks when people ask me the time and I look at my sail

Been on there for about 6 months, never take it off the boom, it's hit the board a couple of times in catapults, takes a lickin, keeps on tickin.