: plumb stem what are the tradeoffs?

'Tis said that a plumb stern will aid in tracking and, as Paul mentioned, increae the WL length relative to overall length. The disadvantage is that they have less reserve bouyancy. In a following sea you'd want the waves to lift the stern rather than roll over it.

: Also, these stems look quite strong without an internal or external add-on
: stem piece. Please comment. Scott

The external stem, sometimes called a false stem, is there to provide a trim piece and to protect the stem from collision damage. You know, should you be piloting at night after after a few beers and not see that dock. Not that I would know.

The inner stem piece provides a structural member to the part of the boat that is most likely to hit the dock, rock or dismounted jet skier. It also provides a uniform faying surface to bond the planking to. Without it the construction of the bow is much more difficult. Each set of planks would have to be fitted to one another and without a uniform reference the bow could easily wander off centerline making for interesting paddling.

Some CLC design do not call for stem pieces, the plywood is just stitched to gether and a false stem of smooze is applied after taping the inside and outside of the stem. In these designs the tape is in effect the inner and outer stem pieces. In my experience getting a good placement of tape for an inner stem is difficult, particularly in a sharp bow. I'm more comfortable with a piece of wood there backing things up. Also if your side planks are not perfectly matched the bow is going to twist off to port or starboard. This may be okay in the stern, but at the bow you're gonna have to look at it every time you paddle.