Ray of No Directionmentions that he's on the lookout for fallen trees to cut up to feed his fire, and says the problem is that he's not the only one looking. But wouldn't the wood be rather too "green" to use straight away in the stove? Don't you get large amounts of tar condensing inside the chimney? Or doesn't it matter, as long as it doesn't trickle down the outside of the boat? The instructions I got with the woodburner we had installed in our sitting room at home stressed the importance of using seasoned logs, where the sap had had a chance to dry out. Perhaps on a boat the risk (of a chimney fire, I suppose) isn't as great as in a house, as the flue is much shorter. A short flue will heat up better than a long flue, thus minimising the tendency for condensation.
This reminded me of Neil's (Herbie) posts earlier this year (here and here) on weight loss by evaporation from some ash logs he'd obtained. Neil draws an impressive graph of weight against time here. After only five weeks his test log had lost nearly a quarter of its original weight.
The difficulty on a narrowboat compared with a house is that of storage. Some boaters, such as Ten Bob Note pictured last year, load their roof with piles of logs; others fill their well deck with them. Unless you're happy to carry a load of logs around with you all year, it must be difficult not to burn them "green".
The picture at the top of this post, by the way, is of a pile of logs-for-the-taking by the towpath of the Llangollen Canal just north of Whitehouses Tunnel. But they're unlikely to be there now - I photographed them two months ago.