All GPS units (Garmin, Velocitek) will generate a "breadcrumb" log file of their tracks. They don't have to be mounted anywhere, they just do it as long as they're turned on and stay on.

There are a number of software solutions to pull the information off the units and put it in a format to go into tracking replay software. (Some of the retrieval and playback software is combined.)

The one that I've always played with is GPS Action Replay. It's a free download. Just Google it.

Kattack uses Garmin eTrex units for no other reason than they're cheap and durable. At the end of the day, they're gathered up by the Kattack employee who then dumps the tracks to their software. The tracks are trimmed to eliminate the in-between race parts and time synchronized. The wind direction and location of the marks are inserted manually (inferred by the tracks), as are the boat labels. The whole process takes about an hour, depending on the number of units.