: Used here it's an internal stringer attached to the inside of the hull at the
: top, used to allow a wide enough surface so deck can be glued (epoxied) to
: it.

Instead of running them for just a few feet in the tips they can also be used full-length. They're often seen on S&G designs. On a design like Bjorn's Black Pearl the deck and hull meet at acute angles (ie: deck flat -, hull angled \). Sheerstrakes are recommended on the plans. You need something to beef up the edge since you'll remove most of it when the edge gets rounded over. On a design that is that long and that low-volume between the small hatches and ocean cockpit you'd never be able to get any fiberglass tape all the way into the ends. You simply just glass the seam in the cockpit. Full-length sheerstrakes made of cedar don't add a lot of weight and provide plenty of area for thickened epoxy. I've installed them before and after glassing (once even before planking the hull). Either way works fine.

Dan