Ship Types & Missions

Commercial shipping is dominated by vessels designed to move cargo efficiently over long distances at the lowest practical cost per tonne-mile. The major types reflect the major cargo categories.

Bulk carriers carry dry unpackaged cargo — iron ore, coal, grain, bauxite — in large holds. They're full-form vessels with high block coefficients, single-screw propulsion, and slow-speed diesel engines; loading/unloading is via shore-based grabs or conveyors. Speeds are modest (roughly 14–16 knots), since the economics favor cargo capacity over speed.

Container ships carry standardized containers stacked on deck and in holds. They're faster (20–25 knots for large vessels) and finer-formed than bulkers, since schedule reliability and speed matter commercially. Propulsion is typically a single large slow-speed diesel.

Tankers carry liquid cargo — crude oil, refined products, chemicals — in tanks. Crude carriers range from small coastal vessels to Very Large Crude Carriers (VLCCs) exceeding 300,000 deadweight tonnes. Tankers are full-form, slow vessels (roughly 14–16 knots); cargo handling is via pipelines and pumps, so hatch openings are minimal.

LNG carriers transport liquefied natural gas at roughly −162 °C in specialized insulated containment systems. Historically steam-turbine propelled (to use boil-off gas as fuel), many modern LNG carriers now use dual-fuel diesel engines. Speeds are typically around 19–20 knots.

RO-RO (roll-on/roll-off) vessels carry wheeled cargo — vehicles, trailers, heavy equipment — driven on and off via ramps, with large internal decks. Speeds are moderate to high (18–24 knots).

Offshore support vessels (OSVs) serve the offshore oil and gas industry: supply, anchor-handling, towing, construction support. They're smaller and highly maneuverable, often with dynamic positioning (DP) systems that hold position without anchoring, using azimuthing thrusters or pod drives.

Tugs provide harbor maneuvering, open-ocean towing, and salvage. They're small, powerful vessels with high bollard pull relative to size, often using cycloidal or azimuthing drives for exceptional maneuverability.

Naval vessels — frigates, destroyers, carriers, submarines — are designed around combat missions rather than cargo economics: high speed (25–35+ knots), survivability, stealth, and mission-specific systems. Hull forms are fine, optimized for speed and rough-water seakeeping, and naval vessels carry a fraction of the payload a commercial vessel of similar displacement would.

The common thread across all of these: mission determines speed, which determines hull fineness; cargo type determines arrangement and loading method; and operating environment determines propulsion configuration and maneuvering requirements.