I vaguely remember reading a thread about this a while back. IIRC this is a fairly common upgrade on Catalinas, but I have no real personal experience with this boat. There are a number of Catalina owners associations you may get a more knowledgeable response if you ask in one of them. For what it is worth adding backing plates is a relatively simple and inexpensive job if you have good access to the underside of the cleats. The fact that you are asking the question probably means that the cost and the time are probably well worth the peace of mind you will get if you do the job.

 

I'd be more concerned about the backing plate than the clear itself.

 

It would not hurt at all to do it. I think the cleats themselves on mine were strong enough, but the way they were attached was not all that good. I did anchor it using the bow cleats but never in a really bad storm. BTW, I think you will find that the undersurface of the foredeck is quite irregular. I used fiberglass resin with chopped fibers (Dynaglass?) to give the backing plate a flat surface to rest against whenever I had to back something up (winches, anchor rollers, etc.).

 

We have a mid 1970s C27. The deck around the bow cleats seems solid (no backing plates though). We moored the boat for 3 years on a river in the upper Chesapeake Bay. The only relevant incident was a very strong wind storm that resulted in our boat dragging its mooring 500yds up the river. We came out to sail and found the boat missing! It was in a marina slip after they rescued it (fortunately it didn’t hit any other boats in the mooring field).

The real answer is that I have no idea if the cleats are strong enough. I bought backing plates online but never put them on because we are now in a slip.

 

I had a mid-1980's Catalina 27. The cleats had small bolts and no backing plates. Not even washers.

Over the course of the few years I owned the boat the wakes in my marina started to deform the fiberglass around the bolts. I just added washers to the back of the cleats and the seemed to fix the problem. A better solution (if you had the room for it) would be to replace the cleats with larger cleats with larger bolts and backing plates. Just make sure if you go through the plywood you seal it properly.

At a minimum, add fender washers to the back of the bolts if they are not already there.