The Kennebec Canoe Company placed serial number 3942 on a 17 foot long canoe in 1911 and on a rowboat in 1929. My guess is that you have the latter. This number is shown on pages 16 and 17 of volume four in the Kennebec ledgers. It was assigned to 14 foot long Kennebec Maine Coast rowboat model that was planked by C. Toulouse on December 21st, 1929 and railed by Toulouse on the same day. The "F 22" (Function number 22 or the keel?) was completed by Thib. on December 28th, 1929. The "F 24" (Function number 24 or the seats?) were completed by F. Thib. on February 14th, 1930. It was painted green. The packing was done by Bresult(?) and it shipped to location "30-72" on February 14th, 1930. This location is probably an order number but we don't currently have enough information to identify it. The scans of these build records can be found by following the links at the attached thumbnail images below. The original Kennebec records are reproduced through the courtesy of the Maine State Museum.
The microfilms and scans of these records were created with substantial grants from the Wooden Canoe Heritage Association (WCHA). I hope that you will renew your membership to the WCHA so that services like this can continue. See http://www.wcha.org/wcha/
to learn more about the WCHA and http://www.wcha.org/join.php
It is also possible that you could have another number or manufacturer if this description doesn't match the boat. The messages and images at http://forums.wcha.org/showthread.php?1453
offer some more details about a similar boat. The link that Paul provided has a good summary of how to value an old canoe. However, old wooden boats usually sell for less than canoes with a similar age and condition. Feel free to reply here if you have any other questions.