I blundered through creating a waypoint in YF and it goes something like this ... You need to be running the v2.011 update ( YellowFin side-scan sonar Model 872 only Update to V2.011 (end 2008) (http://www.metaldec.nl/eng/downloads.html) ~ yellowfin_update_to_v2.011.zip (http://www.metaldec.nl/downloads/yellowfin_update_to_v2.011.zip) ).
Enable Event Input needs to be checked in the Events menu ...
=> (http://limbatus.net/linked/sis-yf-01-tm.jpg) (http://limbatus.net/linked/sis-yf-01.jpg)
Double click on the area of the display where you want the waypoint placed and enter an annotation ...
=> (http://limbatus.net/linked/sis-yf-02-tm.jpg) (http://limbatus.net/linked/sis-yf-02.jpg)
The entries are stored in a file with the same name as the "playback" file with an *.an extension ...
=> (http://limbatus.net/linked/sis-yf-03-tm.jpg) (http://limbatus.net/linked/sis-yf-03.jpg)
(Edit: Too early to be literate.)