John,

what model Timex Ironman is it you use? Pics or a link?

I did not like the Polar audio transfer. I had to be really careful to get a successful handshake so the transfer could start.

Dennis, good initative to build something on your own! I do have a mental image of a Gyro Gearloose creation though
Look forward to seeing pics.

One thing I would like in a sailing watch is a timing function for tacks/gybes and rounding top and bottom mark. On really long courses where you can not see the marks and no distinct landmarks it helps to keep you on the course.
Adjustable countdown timeing is a must have.
Re-sync is nice but not a must have (on a 5 minute sequence I start my watch on the 4 minute signal/flag).
Audio signals for each minute and for the last 15 secs changing every 5 secs is a must have.
Buttons placed where they can not be accidentally operated while sailing is a must have.
A leash that will not open and drop your watch into the ocean is a must have (almost lost my Casio Seapathfinder that way. Lost quite some ground while diving to the reardeck to catch it while gybing).
A leash wide enough to go on your forearm over the drysuit is a must have.
It absolutely have to be waterproof
Looks.. I dont care as long as it functions well and is wearable

Good luck, and keep us informed. Great Blog topic.