You may need to take another look at those serial numbers and the information at
http://forums.wcha.org/showthread.php?791 may help. The Old Town, Carleton, and Kennebec records for this number don't show an 18 foot long canoe with sponsons. I also checked 112591 and the 12591x range.
My guess is that you have the Old Town canoe with serial number 125917. This is an 18 foot long, CS (Common Sense or middle) grade, HW (heavy water) model with red western cedar planking, open spruce gunwales, ash decks, ash thwarts, ash seats, half ribs, a keel, outside stems, sponsons, and bilge keels. It was built between December, 1938 and June, 1941. The original exterior paint was similar to the one shown at
http://www.wcha.org/catalogs/old-town/designs/design37.gif which was known as the design number 37. It shipped on June 18th, 1941 to Fort Wayne, Indiana. A scan showing this build record can be found by following the link at the attached thumbnail image below.
This scan and several hundred thousand others were created with substantial grants from the Wooden Canoe Heritage Association (WCHA) and others. A description of the project to preserve these records is available at
http://www.wcha.org/ot_records/ if you want more details. I hope that you will join or renew your membership to the WCHA so that services like this can continue. See
http://www.wcha.org/about-the-wcha/ to learn more about the WCHA and
http://store.wcha.org/WCHA-New-Membership.html to renew.
It is also possible that you could have another number or manufacturer if this description doesn't match your canoe. The sail rig wasn't mentioned on the build record so that may have been added later. Feel free to reply here if you have any other questions,
Benson