The chine log is the major structural stringer on the lower part of the frames, and the sheer and shelf clamp are the major structural stringers on the higher part of the frames. These three stringers tie all the frames together and spread the loads around, evenly distributing the forces on the hull throughout the other members.
The sheer is the top strake that runs on the outside of the frames. The shelf clamp is the strake that runs on the inside of the frames. These two stringers tie the tops of the frames together into a very rigid and strong unit where forces are distributed throughout the members of the hull.
The sheer and shelf clamp also go by many different names which do serve to denote their position, but are not the most correct of terms for these pieces of wood on a boat.
The sheer is also called the gunwale or outwale. The shelf clamp is often called the inwale. The terms inwale and outwale are rather informative, identifying the strakes that run on the inside and outside of the top of the hull. Gunwale came to be because guns sit over the top of this strake as they aim out towards other vessels. While these names are commonly used, it is still preferred to call them by their correct names: Sheer and Shelf Clamp.
The sheer is considerably thicker than other topside planks and is ideally made out of a single continuous piece of lumber. If the span is too long to make it out of a continuous piece, scarfing is acceptable and preferred over butting.
The shelf clamp is crucial as it ties the sheer to the top of the frame and attaches the deck above it. The sheer and shelf clamp are through fastened, tying the top of the frame to the rest of the members with considerable pressure, negating the posibility for any movement to develop and loosen this junction. The deck then attaches to the top of the shelf clamp, forming a very strong component that ties the whole boat together in unison.
With these two stringers connected, the frames will become incredibly resistant to forces placed upon them as the boat is being tied together.