GA

 General Arrangement

 General Average

GATT

 General Agreement on Tariff and Trade

G/B

 Grain/Bales

GH

Gibraltar Hamburg

GL

 Germanischer Lloyd (German Classification Society)

GLONASS

 Global Navigation Satellite System

GMDSS

 Global Maritime Distress and Safety System

GMT

 Greenwich Meridian Time

GNS

 German North Sea

GO

 Gas Oil

GOC

 General Operator Certificate

GP

 General Purpose

GPS

 Global Positioning System

GPU

 Generator Protection Unit

GRI

 General Rate Increase

GRT

 Gross Registered Tonnage

GT

 Greenwich Time

 Gross Tonnage

GW

 Gale Warning

 Gross Weight