Glue is slippery stuff. After a glue-up and double checking that the parts haven’t moved, you walk away and something decides to get moving. That’s when you turn around, go back, and check one more time. hmmm. Did that. Twice! This time the parts waited until I was completely out of sight.
The slippage of the sheer clamp 
from the previous glue-up is just less than 1/4 inch at the stern end of one of the planks. If it had slipped the other way, I would just plane off the overhanging material, but since it slipped downward on the plank, I must decide what to do. Well, the extending area of the plank could be planed off. That would leave the deck sitting askew in that area, the sheer line spoiled, the boat imbalanced and turning in circles and who knows what else.
Part of boat building, or most any other activity, is learning how to recover from problems. This one is simple. Rive off a shim of wood. Glue it in place. Plane it to shape after the glue sets.
Bob,
Good solution!
I must remember that slip happens 🙂 – it sure does!
I wonder if a little bit of grit sprinkled on the epoxy might prevent, or at least minimize, the slippage? I also have used brads in the past, cut just above the surface of the wood. Works like a charm.
Al