A trunk deck ship is a type of

merchant ship A merchant ship, merchant vessel, trading vessel, or merchantman is a watercraft that transports cargo or carries passengers for hire. This is in contrast to pleasure craft, which are used for personal recreation, and naval ships, which are ...

with a hull that was stepped inward in order to obtain more favourable treatment under

canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flo ...

toll rules then in effect. As those tolls were set by net

tonnage Tonnage is a measure of the cargo-carrying capacity of a ship, and is commonly used to assess fees on commercial shipping. The term derives from the taxation paid on ''tuns'' or casks of wine. In modern maritime usage, "tonnage" specifically r ...

, a measure of volume, and as the tonnage rules did not account for all of the

cargo Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including trans ...

space of such vessels, trunk deck ships 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 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 i ...

s. In 1892, the Sunderland, England firm of William Doxford and Sons Ltd. built its first turret deck ship. Inspired by

U.S. The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territori ...

whaleback ] A whaleback was a type of cargo steamship of unusual design, with a hull that continuously curved above the waterline from vertical to horizontal. When fully loaded, only the rounded portion of the hull (the "whaleback" proper) could be seen a ...

s, one of which had recently visited

Liverpool Liverpool is a city and metropolitan borough in Merseyside, England. With a population of in 2019, it is the 10th largest English district by population and its metropolitan area is the fifth largest in the United Kingdom, with a populat ...

, 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 may refer to: Physical spaces * Hold (ship), interior cargo space * Baggage hold, cargo space on an airplane * Stronghold, a castle or other fortified place Arts, entertainment, and media * Hold (musical term), a pause, also called a Ferm ...

. 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. This vessel was of "three-island" construction with a

forecastle The forecastle ( ; contracted as fo'c'sle or fo'c's'le) is the upper deck of a sailing ship forward of the foremast, or, historically, the forward part of a ship with the sailors' living quarters. Related to the latter meaning is the phrase " be ...

, bridge house, and quarterdeck, extending to the full width of a low-

freeboard In sailing and boating, a vessel's freeboard is 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. In commercial vessels, the latter criterion measured relativ ...

hull. A distinctive feature was a long "trunk" along the centerline, with a breadth of about half the vessel's beam, which connected 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 On a vessel's hull, a strake is a longitudinal course of planking or plating which runs from the boat's stempost (at the bows) to the sternpost or transom (at the rear). The garboard strakes are the two immediately adjacent to the keel on ea ...

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.Some Marine Terminology
(definition 60, TRUNKED DECK STEAMER).

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 (an approximate measure of cargo space) in comparison to their

deadweight tonnage Deadweight tonnage (also known as deadweight; abbreviated to DWT, D.W.T., d.w.t., or dwt) or tons deadweight (DWT) is a measure of how much weight a ship can carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, pro ...

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 the cargo spaces in the trunks 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.Craig, pp. 35-37; Duerkop
Some Marine Terminology
(definition 60, TRUNKED DECK STEAMER).

References

Notes

Sources

* * * * * * . Google books has images of those pages, which contain the chapter entitle
''Trunk Steamers''"> ''Trunk Steamers''
Retrieved 2008-03-26. * .

Photographs

an

photographs of SS ''Trunkby'' from Old Ship Picture Galleries o
www.photoship.co.uk
provenance unknown; location appears to be in

River Avon (Bristol) The River Avon is a river in the south west of England. To distinguish it from a number of other rivers of the same name, it is often called the Bristol Avon. The name 'Avon' is a cognate of the Welsh word , meaning 'river'. The Avon r ...

. {{DEFAULTSORT:Trunk Deck Ship Ship types Shipbuilding Naval architecture