Yes. That's a wine cork in the deck of Red Ranger. Once upon a time (it appears) something like an antenna was mounted there. A hole had been drilled through the deck into the aft cabin. A piece of hardware of some kind had been screwed down outside. [You can see the four mounting holes.] A wire of some kind had been lead inside.
At some point later, the external stuff (and the wire) were removed, leaving a fairly big hole. Slightly smaller than a wine bottle cork. But still big enough.
The hole was "patched" by being filled with what appears to be polysulfide or polyurethane adhesive. It's still very rubbery. Since the gelcoat skin was not really addressed by this "patch", it weeps a tiny dribble of wood-rotting water. Not much. And not often.
We noticed it in the winter because snow piled up and has more time to work it's way into the minute crevices. We can't patch it in the winter because it's too cold to use epoxy or gelcoat.
So. We put a cork in it until the weather is above 70°F. The Commodore whittled the cork to size and pounded it in with the ball-peen hammer. It should keep the snow out. And give the interior wood a chance to dry out.
A few weeks ago, after taking out the aft air conditioner, it became clear that we had a big-old hole in the cabin sole. Ugly. And a tiny draft of chilly bilge air would waft up from below. Altogether unsavory.
[Worse—of course—is the problem of the things that inhabit the deep places in the bilge. Things which are best left unnamed. HP Lovecraft touched on these things. JRR Tolkien describes the Balrog in some detail. I shudder to think of what may dwell in my bilges. Let me whisper "Tsathoggua". Need I say more?]
There are two approaches to solving the problem of the hole in the cabin sole. (Three if you count "ignore it" as a "solution".)
Square it up. Knowledgeable wood-workers told me to use my circular saw to cut four nice, straight edges on that mess.
Fit a piece of teak by rough-cutting and then sanding for 6 hours.
I elected to follow path #2. Rough cut and sand. Option #1 would have expanded the hole. In the long run, I may want a more skilled wood-worker to redo that part of the cabin sole. The sole is beautiful and outside this spot has been nicely maintained.
What I created (eventually) is a tight-fitting 1 1/4" solid teak plug sitting on two 1/2"-thick "stringers" that are screwed up under the cabin sole. You can see two #10 screw heads on the right side.
A "finger hole" in an opening that small would be quite large and hideous. So I put a loop of line through the hole. This can be used to lift it up so that we can inspect the through-hull fitting that's just below that hole.
We can even—with some care—get a wrench or a grease-gun down onto the through-hull fitting to give it the once-per-year twist to be sure it still moves.
The black lines around the hole were put in by some sawzall operator. Eventually, we'll try to remove thee lines with acetone, and (if necessary) sand paper.