What is the importance of the Mejidieh in the novel, Hornblower and the Atropos?

Mejidieh is a Turkish ship of ancient construction. Her mizzen topsail is lateen rigged and she is very beam, short at the water, and high. A two-decker, she carries an impressive number of large cannon—though the number is not specified. Mejidieh appears in Marmorice Bay after Hornblower has completed the bulk of the salvage operation, and threatens to capture Atropos if Hornblower does not hand over all the salvaged gold and silver. Hornblower escapes the larger ship by executing a tricky and dangerous passage out of the bay.