The Drayman is a heavy Merchant Ship. It has bad acceleration and maneuverability, and has to rely on its shields (up to level 4) and 3 turrets for defense. The Drayman was designed for long distance hauls with 10 jump fuel and by far the largest cargo space of all ships, more than 5 times as much as the runner up (Ulysses).
After buying and equipping a Drayman make sure to retain enough cash to actually fill its vast belly. You will now receive Drayman-sized missions from the Merchants Guild, it would be frustrating having to reject most of them because you can't afford the required cargo. Wait with buying the Cargo Expansion until you can make use of it.
Where to Buy this Ship
For 1.2M available at these shipyards: