Hello Donald. I see Al has replied to you, but I'll send this along too even if we're saying the same things.
The number you found may be the serial number, but only a portion of it. Old Town serial numbers are five or six digits, a space, and two digits which are the canoe's length. So, "18" may be the length of your canoe and you may have to do some more digging to find another number or two.
The serial number appears on the stem on the floor of the canoe at each end-- sometimes one end is better than the other and it's nice to be able to compare.
It sometimes is necessary to work at bringing the numbers up (but without damaging the canoe). Wetting with paint thinner can help. Or you could do a rubbing--- place paper over the stem and go over the back of it with soft pencil or crayon or charcoal. A digital picture will sometimes see what the eye cannot. Or you can post a picture here, and several eyes may form a consensus. If one or two numbers aren't clear, we can check several records until we find the one that fits your boat.
Pictures are always nice to see. If they're in your computer, you can post them in this forum. Scroll down, below the box you type into, and you'll see "manage attachments" in the second box below this. Click on that to get a browse window and you can select the views you want us to see.
It's very cool that you have "the family canoe", creating happy memories for successive generations.
Kathy