Bulk Carrier Specifications Guide

What a vessel’s specifications describe

When an owner offers a vessel, the ship’s particulars list a fixed set of measurements that tell a charterer what the ship can carry and where it can go. This guide defines that vocabulary: the weight terms, the capacity terms, the cargo-handling terms, and the structural measurements. The geometric dimensions (length, beam, draught, depth) are defined in full on the vessel dimensions page; this guide covers the rest and ties them together.

The table below sets out the core specification terms, what each measures, and the authority that defines or records it. Classification societies, principally Lloyd’s Register, DNV, and ABS, survey the hull and record the particulars; the tonnage and load line figures sit under IMO conventions.

Term	What it measures	Unit	Reference
Deadweight tonnage (DWT)	Total weight a vessel can carry: cargo, bunkers, stores, fresh water, and crew, at the summer load line	tonnes	Assigned at the summer mark under the Load Line Convention
Lightweight (LWT)	Weight of the ship itself, empty: steel, machinery, and equipment	tonnes	Builder and class society
Displacement	Total weight of water the hull displaces; lightweight plus deadweight when fully loaded	tonnes	Naval architecture; class society
Gross tonnage (GT)	A volumetric measure of the ship's total enclosed space, used for regulation and fees	dimensionless index	IMO Tonnage Convention 1969
Net tonnage (NT)	Volumetric measure of the cargo-earning space, derived from GT	dimensionless index	IMO Tonnage Convention 1969
Grain capacity	Cubic capacity of the holds for a free-flowing cargo that fills every corner	cubic metres	Class society capacity plan
Bale capacity	Cubic capacity for a cargo that does not flow into the frames and brackets, so slightly less than grain	cubic metres	Class society capacity plan
Holds and hatches	Number of cargo holds and the deck openings that serve them	count	Class society general arrangement
Gear	Whether the ship carries its own cranes (geared) or relies on shore equipment (gearless)	configuration	Ship particulars

Weight terms: deadweight, lightweight, displacement

The three weight terms are easy to confuse. Lightweight is the empty ship. Deadweight is everything the ship can add on top of that: cargo plus the bunkers, stores, and water needed for the voyage. Displacement is the sum of the two, the total weight of water pushed aside by the fully loaded hull. For a charterer the operative figure is cargo deadweight, which is deadweight minus the bunkers, stores, and water the ship must carry, and which is always a little below the headline DWT. The deadweight tonnage page works through the difference with examples.

Gross and net tonnage are a different kind of figure entirely. Despite the name they are not weights but volumetric indices defined under the IMO Tonnage Convention, used to set canal dues, port fees, and the thresholds for many regulations. A vessel’s GT and NT travel with it on the tonnage certificate.

Capacity terms: grain and bale

Cubic capacity decides whether a light cargo fills the holds before the ship reaches its deadweight. Grain capacity is the total hold volume available to a free-flowing cargo that runs into every corner and frame space. Bale capacity is the smaller figure for a cargo that stacks but does not flow, leaving the spaces between frames and brackets unused. The gap between the two is typically a few per cent.

Whether weight or volume is the binding constraint depends on the cargo’s stowage factor: the cubic space one tonne occupies. A dense cargo such as iron ore reaches deadweight with the holds part empty; a light cargo such as wood pellets fills the cubic capacity first and leaves deadweight unused.

Cargo handling: holds, hatches, and gear

The number of holds and hatches, and whether the ship is geared, decide how and where it can work cargo. The reference table below reads these across the mainstream classes, following the same Clarksons Research and Lloyd’s Register class data used on the individual class pages.

A geared vessel can self-discharge at a minor port with no shore loader or grab, which is why the smaller classes stay flexible across the world’s lesser-equipped berths. The large ore and coal terminals that Capesize ships serve have heavy fixed shore equipment, so those ships are built gearless to save weight and gain cargo space. Hatch design matters too: wide, box-shaped holds with large hatch openings speed loading and grab discharge, and they are covered by hatch covers that must be weathertight under the load line regime.

Where to go next

For the geometric measurements, read vessel dimensions; for the weight headline, deadweight tonnage; and to compare the classes by size and trade, the size comparison. The bulk carriers hub holds the full catalogue. When you have a cargo to move, tell us about it and our desk will match it to the right specification.