Admiral Hood transfers his flag after damage

If Admiral Hood's flagship were crippled by midships hits, which ship would receive his flag?

He would move to the nearest suitable squadron ship, which would then become the flagship.

No fixed replacement ship was required. Admiral Hood would transfer his flag to the nearest suitable vessel in his squadron. That ship would move from private-ship status to serving as the flagship. The procedure preserved command continuity after the original flagship was crippled.