In designing a sailing watch remember what Reg White wrote in the 60's "All yacht timer will eventually leak around the buttons, treasure the Rolex Submariner" translation any mechanical penetrations of the case will eventually leak.

Below are some features I like:

My favorite sailing watch is the Timex Victory, it has a big red START button on the front. Because it is programmed for 5 minute increments , I can't use it all the time.

Take a look at the Nike Typhoon (tide model). It has multiple independent programmable timers. I programmed the timers for 1, 3,3, 5 and 9 minutes. It's like having preprogrammed times. You go to start mode and then page through the timers to the time you want. The advantage is if something screws up (restart, postponement, you missed a flag) you don't have to stop and reset your timer, you just page to a new timer. The active timers controls the display and sounds. The case on the typhoon is interesting. The case and the band are one. The only penetration is the back. The case has pushers under the plastic of the band/case skin to operate the micro switches on the movement. The display, electronics and battery are a single module that is seperate from the case. When the case/band wears out or you crack the crystal you replace it.

I think the Garmin 201 or the Suunto M9 have the best computer interface, gold contacts on the outside of the case and a matching holder. The contacts provide battery charging and a serial port to the movement. The holder touchs the contacts and provides standard connects for serial and battery charger.

My SWISSSAIL had a button lockout. You rotated the bezel to set the mode and clicks between the modes was last mode, buttons inactive. That way you didn't reset your watch halfway through the start sequence. Everything else about that watch sucked. It was hard to read, use and it leaked.

I have seen old PDA's used in Labs as Timers and data loggers. If you could build a waterproof case, you would have all the programmability features, and interfaces you would need to play for a couple of years.