In the books
In the A Song of Ice and Fire novels, the Myraham is a fat-bellied trading cog from Oldtown, carrying fruit, spices, wine from the Arbor, cloth, seed, feathers from the Summer Isles and musical instruments to trade for iron ore. Her captain is fat-bellied southron merchant.
Once the captain concludes his business, he discovers that the Myraham and other merchant vessels are not allowed to depart at Balon Greyjoy's order; Balon wants no word of the hosting of the warships to reach the mainland before he is ready to strike. Thus the Myraham is detained for more than six months at Lordsport.