Tonnage

• Two Primary Types of Tonnage– Volume

– Weight

Tonnage

• Volumetric Tonnage– Used to determine the earning

capacity of vessels– Derived from the word “Tun” in the

13th century. A Tun was a wine cask or barrel

– 100 cubic feet is equal to 1 ton

Tonnage

• Volumetric Tonnage– Used to determine port fees, dock fees,

dry docking charges, etc

– The original idea was to have fees based on the vessel owners ability to pay (the vessels ability to earn)

Tonnage

• Gross Tonnage

– Internal volume of vessel less certain exempted spaces• Example:

– A barge is 100’ x 50’ x 10’– Internal volume is 50,000 cu ft– Gross tonnage is 500 tons

Tonnage

• Net Tonnage– Remaining tonnage after non-earning spaces

are removed from the Gross Tonnage– Non-earning spaces (exemptions) are:

• Doublebottoms

• Forepeak and Aftpeak (if for water ballast only)

• Poop, Bridge and Forecastle (if fitted with tonnage openings

Tonnage

• Non-earning spaces (cont’d)– Shelter deck (if fitted with tonnage openings)– Passenger spaces on the deck above the

uppermost continuous deck– Other miscellaneous spaces including

companionways, skylights, wheelhouses, vents and some water closets

Tonnage

• Deductions– Crew and working spaces– Machinery space (principle deduction)

Tonnage

• Tonnage Openings– Nominally non-water tight

• No gasket used

• Normally secured with bolt hooks

• May be secured with wooden battens (not seen much any more

Tonnage

Tonnage

• Ship Owners and designers work to minimize Net Tonnage

• Some rules in the calculation of tonnage can be made to work to the ship owners advantage– By designing the vessel with the machinery

space between 13% and 20% of the total Gross Tonnage, 32% of the gross tonnage may be deducted

Tonnage

• In order for crew and working spaces to be deducted, the builder must certify that the space is ONLY for crew or working– A plaque will be placed in or on the space

indicating this• Law requires 120 cu ft and 16 sq ft of space for each

crew member

Tonnage

• Other Volumetric Tonnages– Suez and Panama Canal Tonnages

• Each has their own rules, but in general will be greater than the Net Tonnage

Tonnage

• Weight Tonnages (Long Tons or Metric Tons)– Displacement Tons– Deadweight Tons– Light Ship Tons

Tonnage

• Displacement Tons– The weight of water displaced by the hull, it is

exactly equal to the weight of the vessel and its contents

Tonnage

• Deadweight Tons– The amount of water, cargo, fuel and stores a

vessel can carry when fully loaded.

Tonnage

• Light Ship Tons– The weight of the empty ship. The

displacement of of a vessel with no cargo, crew, stores, fuel, water, and ballast.

Tonnage

• Review– Tonnage as a volumetric measurement is in

units of 100 cu ft = 1 Ton– Tonnage as a weight measurement is in units of

Long Tons or Metric Tons.