Howie, I have a couple more questions based on your other responses..

1) If you lay a strip across 10/11 station on various spots on the deck and bottom of the hull what is the gap variation with 10.5

2) Is the gap the same on the starboard and port side?

3) If your stations has a waterline mark, sight down side and see if the waterline mark lines up.

My guess is you're off on the placement of the 10.5 station by the thickness of your station.

In several of the Nick Schade designs I built, you measure the strongback mark of the stations starting from the end of the strong back toward the middle from both sides. The two center stations will have a spacing of 11 and 1/4 inches instead of the 12 inch spacing. (ie.. This is due to the thickness of the station). The side of the stations facing towards ends of the strongback should be placed and aligned with the strongback mark.

This is why I think you maybe off the station thickness..

I hope this helps!
K.Greer