There's a new Timex triathlon "watch" that is waterproof to 50 meters. The logging capabilities are a bit unclear, but the hardware could be made to work for speedsailing, given the right firmware.

It costs a bit more than the GT-31, but it is smaller and doesn't need an Aquapac. Locosystech has put a nice amount of effort into speedsailing support in their firmware, but their current product isn't any more waterproof than the original GT-11.

Since the Timex is a new product, this might be a good time to contact them to see if they can add a speedsailing mode and adequate data logging.

The SD memory card in the GT-11/31 is a great convenience though... I've had my BGT-11 since June 2007 and the 1GB card I started with still has over 300MB of free space. Most of my sessions are "uninteresting" in that they never get reviewed on a computer. However, I like having a log of all my sessions without the hassle of actually having to transfer the log to a computer after every session. This is potentially where the Timex wouldn't be as convenient (assuming the log size is limited).

In summary: I doubt the Timex is currently a valid contender for speedsailing, but it's a promising product development.