Symbol Analysis
If Arthur is a relic, then the ship that carries his remains back to England is a sort of reliquary. Tennyson has a reverent attitude toward this ship, naming it "sacred bark" (374) and giving it his blessing so that no storms will harm it and that his "beacon" will "guard it home" (372).
Not only does the ship function as a sort of grave for Arthur, but it also symbolizes the idea of transition from life to death. So, just as a ship crosses the borders between lands via rivers, this ship has also ferried Arthur across the border from life to death in Tennyson's view.