IMHO this the the best starttimer around:
http://www.sailingclothingstore.co.uk/Sailing_Watches/pr28055_sc343.aspx
Its got big digits, its loud, straps around the boom and flips over easily. very easy to use, has presets, big buttons, sync, last 10-sec beep countdown, etc.
I also have a Suunto Mariner for everyday watch which is also good as a timer but I prefer to have one on the boom for the crew to operate.