Trunk deck ship
Encyclopedia
A trunk deck ship is a type of merchant ship with a hull
that was stepped inward in order to obtain more favourable treatment under canal
toll rules then in effect. As those tolls were set by net tonnage
, a measure of volume, and as the tonnage rules did not account for all of the cargo
space of such vessels, they incurred lower tolls than more conventional ships of equivalent capacity. When the measurement rules were changed, the type was no longer built.
s. In 1892, the Sunderland, England
firm of William Doxford and Sons Ltd. built its first turret deck ship. Inspired by U.S.
whaleback
s, one of which had recently visited Liverpool
, Doxford built a ship which had a curved hull form which was stepped in above the waterline. The narrow part of the hull, called a turret, was part of the hold
.
Four years after the first turret deck ship, the first trunk deck ship appeared. SS Trunkby, completed in 1896, was built by Robert Ropner
at his shipyard at Stockton-on-Tees
. She was of "three-island" construction with a forecastle
, bridge house
, and quarterdeck
, extending to the full width of a low-freeboard
hull. Her distinctive feature was a long "trunk" along the centerline, with a breadth of about half the vessel's beam, which connecting the three elements of the superstructure. This trunk was stepped inward from the sides of the hull. That trunk was not a deckhouse or superstructure, but was part of the hull, and contained cargo space.
In hull form, trunk ships resembled turret deck vessels, differing mainly in eliminating the curves and joining the above-water horizontal part of the hull with the vertical strake
s and sides of the trunk by right angles. The similarity was such that Doxford, builder and operator of the turret decks, sued Ropners for patent infringement.
Trunk deck ships had a low net tonnage
(an approximate measure of cargo space) in comparison to their deadweight tonnage
capacity (weight of cargo). Net tonnage is a computation of volume, and the method of measurement used at the Suez Canal
to determine tolls was based on a measure of net tonnage which excluded some of the cargo spaces of these unconventional hulls. Trunk deck ships therefore paid less in tolls. In 1911 the toll measure changed at Suez, and construction of the type ceased.
Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
that was stepped inward in order to obtain more favourable treatment under canal
Canal
Canals are man-made channels for water. There are two types of canal:#Waterways: navigable transportation canals used for carrying ships and boats shipping goods and conveying people, further subdivided into two kinds:...
toll rules then in effect. As those tolls were set by net tonnage
Tonnage
Tonnage is a measure of the size or cargo carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume...
, a measure of volume, and as the tonnage rules did not account for all of the cargo
Cargo
Cargo is goods or produce transported, generally for commercial gain, by ship, aircraft, train, van or truck. In modern times, containers are used in most intermodal long-haul cargo transport.-Marine:...
space of such vessels, they incurred lower tolls than more conventional ships of equivalent capacity. When the measurement rules were changed, the type was no longer built.
Background and design
Trunk deck ships were influenced by (some would say copied from) turret deck shipTurret Deck Ship
A turret deck ship is a type of merchant ship with an unusual hull, designed and built in the late 19th and early 20th centuries.The hulls of turret deck vessels were rounded and stepped inward above their waterlines. This gave some advantages in strength and allowed them to pay lower canal tolls...
s. In 1892, the Sunderland, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
firm of William Doxford and Sons Ltd. built its first turret deck ship. Inspired by U.S.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
whaleback
Whaleback
A cargo steamship of unique design, with a hull that continuously curved above the waterline from vertical to horizontal leaving, when fully loaded, only the rounded portion of the hull above the waterline, was unofficially called a "whaleback". With sides curved in towards the ends, it had a...
s, one of which had recently visited Liverpool
Liverpool
Liverpool is a city and metropolitan borough of Merseyside, England, along the eastern side of the Mersey Estuary. It was founded as a borough in 1207 and was granted city status in 1880...
, Doxford built a ship which had a curved hull form which was stepped in above the waterline. The narrow part of the hull, called a turret, was part of the hold
Hold (ship)
thumb|right|120px|View of the hold of a container shipA ship's hold is a space for carrying cargo. Cargo in holds may be either packaged in crates, bales, etc., or unpackaged . Access to holds is by a large hatch at the top...
.
Four years after the first turret deck ship, the first trunk deck ship appeared. SS Trunkby, completed in 1896, was built by Robert Ropner
Sir Robert Ropner, 1st Baronet
Sir Emil Hugo Oscar Robert Ropner, 1st Baronet 1838-1924, was a British shipbuilder, shipowner, and Conservative Member of Parliament. He was known simply as Robert Ropner....
at his shipyard at Stockton-on-Tees
Stockton-on-Tees
Stockton-on-Tees is a market town in north east England. It is the major settlement in the unitary authority and borough of Stockton-on-Tees. For ceremonial purposes, the borough is split between County Durham and North Yorkshire as it also incorporates a number of smaller towns including...
. She was of "three-island" construction with a forecastle
Forecastle
Forecastle refers to the upper deck of a sailing ship forward of the foremast, or the forward part of a ship with the sailors' living quarters...
, bridge house
Bridge (ship)
The bridge of a ship is the room or platform from which the ship can be commanded. When a ship is underway the bridge is manned by an OOW aided usually by an AB acting as lookout...
, and quarterdeck
Deck (ship)
A deck is a permanent covering over a compartment or a hull of a ship. On a boat or ship, the primary deck is the horizontal structure which forms the 'roof' for the hull, which both strengthens the hull and serves as the primary working surface...
, extending to the full width of a low-freeboard
Freeboard (nautical)
In sailing and boating, freeboardmeans the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship...
hull. Her distinctive feature was a long "trunk" along the centerline, with a breadth of about half the vessel's beam, which connecting the three elements of the superstructure. This trunk was stepped inward from the sides of the hull. That trunk was not a deckhouse or superstructure, but was part of the hull, and contained cargo space.
In hull form, trunk ships resembled turret deck vessels, differing mainly in eliminating the curves and joining the above-water horizontal part of the hull with the vertical strake
Strake
A strake is part of the shell of the hull of a boat or ship which, in conjunction with the other strakes, keeps the sea out and the vessel afloat...
s and sides of the trunk by right angles. The similarity was such that Doxford, builder and operator of the turret decks, sued Ropners for patent infringement.
Advantages and disadvantages
As with turret deck ships, the design of the trunk deck ships was said to maximize strength while reducing the amount of steel needed for construction. Disadvantages included the narrow hatches atop the trunk, which inhibited efficient loading and unloading. The low freeboard meant smaller waves could board the ship, and the bridge and superstructure therefore had to be stronger to resist wave action.Trunk deck ships had a low net tonnage
Tonnage
Tonnage is a measure of the size or cargo carrying capacity of a ship. The term derives from the taxation paid on tuns or casks of wine, and was later used in reference to the weight of a ship's cargo; however, in modern maritime usage, "tonnage" specifically refers to a calculation of the volume...
(an approximate measure of cargo space) in comparison to their deadweight tonnage
Deadweight tonnage
Deadweight tonnage is a measure of how much weight a ship is carrying or can safely carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew...
capacity (weight of cargo). Net tonnage is a computation of volume, and the method of measurement used at the Suez Canal
Suez Canal
The Suez Canal , also known by the nickname "The Highway to India", is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea and the Red Sea. Opened in November 1869 after 10 years of construction work, it allows water transportation between Europe and Asia without navigation...
to determine tolls was based on a measure of net tonnage which excluded some of the cargo spaces of these unconventional hulls. Trunk deck ships therefore paid less in tolls. In 1911 the toll measure changed at Suez, and construction of the type ceased.
Sources
. Google books has images of those pages, which contain the chapter entitled Trunk Steamers. Retrieved on 2008-03-26..Photographs
- Bow 3/4 and Stern 3/4 photographs of SS Trunkby from Old Ship Picture Galleries of www.photoship.co.uk; provenance unknown; location appears to be in River Avon (Bristol).