Hundreds of upscale condo conversions and well-maintained boat slips have transformed the Charlestown Navy Yard. But until the Navy Yard Bistro opened, the restaurant scene hadn’t quite gotten its sea legs. The bistro offers recognizable favorites such as roast chicken and hanger steak, alongside more-exotic preparations of tuna tartare and miso-marinated salmon served with wasabi-spiked crème fraîche. Hardly culinary gymnastics, but each dish is thoughtfully prepared with well-balanced flavors and just-right portions. Service is casual and friendly, which suits the something-for-everyone menu and low-key décor. And with entrées hovering around $15, the bill won’t rock the boat.