Hydrogen Maritime Glossary

Key terms and definitions for hydrogen-powered shipping

A

AiP (Approval in Principle): A statement from a classification society confirming that a design or concept is feasible and complies with applicable rules and standards. An early-stage approval that precedes full type approval.

B

Bunkering: The process of refueling a vessel. For hydrogen ships, this involves transferring compressed or liquid hydrogen from shore facilities, trucks, or bunker vessels to the ship’s storage tanks.

BoG (Boil-off Gas): Hydrogen gas that evaporates from liquid hydrogen storage due to heat ingress. A key consideration for LH2 tank design and operational management.

C

CAPEX (Capital Expenditure): The upfront investment required to build or acquire assets. For hydrogen vessels, this includes the additional cost of fuel cell systems, hydrogen storage, and associated safety equipment compared to conventional propulsion.

CH2 (Compressed Hydrogen): Hydrogen gas stored under high pressure, typically at 350 or 700 bar. Common in smaller maritime applications and swappable container systems.

CTV (Crew Transfer Vessel): A vessel used to transport personnel to and from offshore installations. Several hydrogen CTVs are now operational, primarily in the North Sea.

D

DNV: A leading classification society headquartered in Norway. Active in developing rules and guidelines for hydrogen-fueled vessels.

E

ETS (Emissions Trading System): The EU’s cap-and-trade system for greenhouse gas emissions. Maritime shipping was included in EU ETS from 2024, creating financial incentives for zero-emission fuels.

Electrolyzer: Equipment that uses electricity to split water into hydrogen and oxygen. Green hydrogen is produced using electrolyzers powered by renewable electricity.

F

Fuel Cell: An electrochemical device that converts hydrogen and oxygen into electricity, water, and heat. PEM fuel cells are most common in maritime applications.

FuelEU Maritime: EU regulation requiring the gradual reduction of greenhouse gas intensity of energy used onboard ships, creating demand for low-carbon fuels including hydrogen.

G

GHG (Greenhouse Gas): Gases that trap heat in the atmosphere. Maritime shipping accounts for approximately 3% of global GHG emissions.

Green Hydrogen: Hydrogen produced through electrolysis powered by renewable energy sources. Zero-emission production pathway.

I

IGF Code (International Code of Safety for Ships Using Gases or Other Low-Flashpoint Fuels): IMO’s international code establishing safety requirements for gas-fueled ships. Currently being updated to include hydrogen-specific provisions.

IMO (International Maritime Organization): The United Nations specialized agency responsible for the safety and security of shipping and the prevention of marine pollution.

L

LH2 (Liquid Hydrogen): Hydrogen cooled to -253C and stored as a cryogenic liquid. Offers higher energy density than compressed hydrogen but requires specialized cryogenic infrastructure.

LR (Lloyd’s Register): A major classification society active in hydrogen maritime approvals and standards development.

M

Metal Hydride: A compound formed when hydrogen is absorbed into a metal alloy. Offers solid-state hydrogen storage at low pressure and ambient temperature.

MW (Megawatt): Unit of power. Maritime fuel cell systems are measured in kilowatts (kW) or megawatts (MW). 1 MW = 1,000 kW.

P

PEM (Proton Exchange Membrane): The most common type of fuel cell for maritime applications. Operates at relatively low temperatures (60-80C) with fast start-up times.

S

SOFC (Solid Oxide Fuel Cell): A high-temperature fuel cell type (600-1000C) offering higher efficiency but slower start-up than PEM. Being evaluated for larger maritime applications.

T

Type Approval: A certification from a classification society confirming that a product meets the applicable standards for a specific marine application. Higher level of approval than AiP.

TEU (Twenty-foot Equivalent Unit): Standard measure of container ship capacity. One TEU equals one standard 20-foot shipping container.

W

Well-to-Wake: The complete lifecycle assessment of a fuel, from production (well) to combustion or use onboard (wake). Important for comparing the true environmental impact of different marine fuels.