[Psml] GPS Projection Question

[C. Henry Depew]

Greetings!
     Probably I missed the information, but I am would like to know 
what projection and datum are the default for the GPS units on the 
market for use by those boating.  Do all the vendors use the same 
projection and datum?  Anyone know or know where to go to find the 
answer(s)?  I looked at the available literature and could not find 
the information (fine print in the appendix someplace?).

C. Henry Depew
sisu26 at nettally.com