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I assume this on the topside (side of the boat) and we must rotate the picture 90 deg clockwise? Does the crack show on the gunwale or is it only on the outside topside.
If it is across the gunwale too and under the rubrail then yes I would worry it being a structural crack and it would require reinforcement of several new layers of fiberglass over a longer area. If not it might have been cause by a hit cracking the outer layer on FG.
No matter what you must repair it to keep water from intruding.