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Jordi -

That appears to be the "Sprue" hole.

When the boat was manufactured, they inserted the foam injector head in to this hole and foamed the hull cavity. It also used to allow excess foam to escape.

This cover should be sealed. I would use a marine grade polysulfide based sealant(e.g.BoatLife LifeCaulk) to the underside and edge of the cover.

Try to dry the area before sealing.

The bow locker drain is standard. If the drain tube is leaking, it should be replaced.