I bought a 1976 O'Day 22 last fall, and there is a hole I don't understand in the keel. It is about 1" in diameter, located near the lowest point of the keel on the starboard side. Can anyone tell me what this is about?

It's a clean hole, definitely put there intentionally. Does it need to be patched before I put in this spring? I've attached a picture of it.
It's a clean hole, definitely put there intentionally. Does it need to be patched before I put in this spring? I've attached a picture of it.
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