The smile applies to almost any sailboat built with an external ballast (lead) bolted to a fiberglass keel stub. When the boat was manufactured the lead to fiberglass union was bedded with an adhesive sealant, probably 3M 5200. Over time a separation on the leading edge can develope leading to a smile line at the union. This can be "ho hum", in most cases, but if it develops too far can lead to water intrusion into the keel stub and if the keel stub has been reinforced with a wooden member then rot can develop resulting in loosening of keel bolts.
So, I guess the caution you were given says look for the smile, if it is there, then check the keel bolts as these can be signs of an expensive to repair situation. Keel bolt fixing nuts are designed to take a specific torque, based on the number and size of bolts and is something a surveyor can check and report on for you.
Hope this helps.
ps. Go buy Don Caseys book "Inspecting the Aging Sailboat", it will be a valuable guide as you shop around for a boat.

 

The Catalina smile (or the C&C smile) is something seen on many an older fin keel boat.. it's a slight separation between the bolted on keel and the hull itself, often manifesting itself at the front end of the keel joint, hence the term 'smile'.

Here you can see the start of a smile repair.

It's not usually a fatal flaw, but can be something that needs attention every few years if there's flex in that area over time.

Keel bolts are tougher.. if they look bad from inside the boat then you know you've got an issue... but at times they can look fine but be corroded in areas you can't see.. visible separation along the entire keel root might make one become concerned that the bolts have been wet at the joint and may have suffered corrosion. Unfortunately the only way to be absolutely certain is to drop the keel and have a look... not a small job.

 

Part of the "Catalina" reference is because Catalina sailboats of a certain vintage suffered especially severe separation. The reason for this was that they encapsulated a wood block into the keel stub. Over time, as stresses caused the keel bolts to wiggle a bit, and the polyester resin to crack slightly, water ultimately intruded into the wood, leading to rot. As the wood spacer rotted, the keel would sink a bit, leading to separation between the keel and the keel stub.

Catalina ultimately abandoned the use of wood spacers in the keel stub, and many owners of the older boats have removed the wood and filled the space in with epoxy.

I do not know exactly what model years were affected. I know that my boat was built well after Catalina abandoned use of wood in the keel stub. You'll have to do some research to find what years had the wood in the keel stub.

 

We had one on our boat, which required weeks of work and a few thousand dollars to repair correctly (in our eyes). Here's a link to a post with pictures of our smile: Take to the sea: Stranded at the edge of the world. When we pulled it out of the water, all you could see was a hairline crack to indicate its presence. It wasn't until we ground it back that we discovered the large affected area in the photo.

The previous owner had clearly patched this up with something in the past, likely 5200 or even some kind of Bondo substance, but it didn't hold up over time and usage (and maybe a slight plowing into a sandbar, but I'll never admit it). This caused water intrusion into the hull material under the fiberglass (in our case cedar strips, but Catalinas are no doubt different). Left unchecked this would have rotted our hull out from under us.

The repair isn't complicated, but it did require a haul-out and the patience to dry it out fully before checking the keel bolts and sealing it back up. If you are looking at a fin keeled boat, it's something that's worth looking for.

 

Here is a pic of a smile on my boat before I bought it;

Here are some pics showing why the smile is a bad thing:

and here is the boat being repaired (on the previous owner's dime);

Finally, here is a pic taken 2 years later, when I had the bottom soda blasted.

I hope this helps explain

 

I understand the "Smile" now. Thanks