Bertram's new 37 bears more than a family resemblance to the prize-winning 54- and is proving just as popular After 25 years, the diminutive warhorse that started it all, the venerable, if occasionally wet Bertram 31, has been retired. Certainly there were practical reasons- too costly, too dated, too predictable. But the move has its symbolic origins as well, as in "out with the old and in with the new": a new corporate masthead, new lizard skin and Novasuede, new laser discs, stereo TVs and digital tachs, new core materials, new colors and new computerized routers. The little gem that launched the Bertram line and paved the way for successively larger Bertrams has died, but its spirit lives on in the new midsized jewel that will dictate the direction of the Bertram "empire" through the 1990s and reassert Bertram's tradition as a trendsetter-the 37 Convertible.