We go ashore and cut/split/stack our wood. Then, we truck it to the dock and wheel it down to the boat. A lot of labor involved, but very satisfying right now at 13 degrees and I'm a T-shirt typing this. Problem Solved! To those who suggested a draft problem, you were right! I added on 4 extra feet today and a better smokehead/cap with perfect results! Very excited that the CO levels have been a persistent zero on the meter all night long with howling NE winds, blowing snow, freezing fog and cold temps. Opening up to air out in this weather would have made me a grumpy guy out here. As to neighbors "borrowing" wood... let's hope they don't. Luckily, they don't have wood heat. It's very atypical to have wood heat on a boat. Thank you very much to everyone that posted with all the great ideas. Through process of elimination, the draft of the chimney seemed most likely. The original terminus of the chimney was about even (maybe an inch below) the highest part of the heated boat. With the extra 4 ft attached, it now towers over the entire boat. Maybe this was the important point. Either way, no more CO. Thanks!