Without seeing the picture I'd guess its an International One Design. Its
actually based on a 6-meter, and was originally used for a series of team
races
between Bermuda and Long Island Sound.

I have not seen the magazine advert either, but there is an active fleet of
IODs in Bermuda, making it quite likely that it is an IOD in the photo used in
the ad.
Ali Meller
http://www.sailing.org/int505/graphic.htm