From A Wiki of Ice and Fire
- Galley, Vessels larger than boats, that are primarily propelled by oar power. They are used for warfare, trade and piracy. Due to their low setting they were primarily coastal ships, prefer threading through archipelagos rather than risking even a moderate sea. their large rower crew made them maneuverabil and swift but also required frequent stops for food and water. The galley has supplemental sails to replace or augment the effort of the rowers, particularly during long journeys. The ability to travel swiftly without regard to the direction or strength of the wind became invaluable for daylight expeditions across open water. (Real-life, practical upper limit for a galley fast and maneuverable enough for warfare was around 25-30 oars per side. By adding another level of oars, the galley could be made shorter with as many rowers, while making them strong enough to be effective ramming weapons.)
- War Galley, are larger than normal Galleys and carry more tonnage as a result of being equipped with siege weapons like ballista or catapults, and having a larger compliment of oarsmen and soldiers onboard. The standard tactic for engaging is to disable the opposing ships' sails then ram and board it. They are presumably the kind of ship that GRRM has compared to Venetian/Byzantine dromonds of war
- Longships, are smaller type of Galley, primarily used by the Ironborn. They are long, narrow, light, wooden boat with a shallow-draft hull designed for speed. The ship's shallow draft allowed navigation in waters only one metre deep and permitted beach landings, while its light weight enabled it to be carried over portages. Longships were also double-ended, the symmetrical bow and stern allowing the ship to reverse direction quickly without having to turn around; this trait proved particularly useful in northern latitudes where icebergs and sea ice posed hazards to navigation. Longships were fitted with oars along almost the entire length of the boat itself. Later versions sported a rectangular sail on a single mast which was used to replace or augment the effort of the rowers, particularly during long journeys. GRRM has compared them to Viking longboats.
- Cog, is mostly propelled by sails, which made it difficult to sail, especially upwind, and it was hostage to breezes and currents in a way that the swift galley was not. however it could better manage rough seas and its small crew and ample storage space gave it greater freedom of movement. making it perfect for trade or equipment transport.
- Carracks, large ocean-going vessel. Stable in heavy seas, and roomy enough to carry provisions for long voyages.
- Summer Island Swan ship, large ocean-going vessel designed and built in the Summer Islands. it has large, white sails and figureheads that more often than not depicted birds. They sail very well, but when becalmed, they are helpless. -
Note, the Some of the descriptions are based on real life parallels.