Not a Kennebec serial number format. Charles River builder. Seems all canoes with extreme recurve were called "Kennebec" before people realized what others built on the Charles. For one example of similar canoes:
Many with this format don't have other identifying marks, or they have ones that are questionable. I know one though with J.R. Robertson tag, Robertson thwart stamp and 3-part serial number just like yours. So even though Robertson also used 2-part serial numbers, all with 3-part numbers may be Robertson.
The Kennebec records do not show a serial number 52735. The Old Town canoe with this number is 18 feet long. The serial number format with two embedded spaces is most commonly associated with Charles River area builders like Robertson and the elongated 'torpedo' stems were also popular with these builders as mentioned previously. Pictures would probably help resolve this.