Wineglass sterns are an elegant detail. Many boats have them as they make a fine transition of form from a buoyant stern to a skeg or keel. Here is one on William Penn's gig. They allow a designer to create a long straight keel which improves tracking when rowing or sailing, while allowing rocker for minimal wetted surface and turning. A wineglass stern allows a longer more secure mount for steering gear. Reducing width at bow & stern waterlines also reduces the amount of power necessary to drive the craft through the water. This is an important consideration for human powered boats. Both the tuck-up and the shadboat have more of a "champagne" glass, a bit wider than a wine glass.