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 in strength and allowed them to pay lower canal tolls under tonnage measurement rules then in effect. The type ceased to be built after those rules changed. The last turret deck ship in existence was scrapped in 1960.
Development
Turret deck ships were inspired by the visit of the US whaleback vessel Charles W. Wetmore to Liverpool in 1891.[1] Like others of the type, Wetmore had a hull in the form of a flattened cigar, with a continuous curve above the waterline to where the sides met amidships.[2] The superstructure atop the hull was in round or oval "turrets", so named because of their resemblance to gunhouses on contemporary warships.[3]
In 1893
The design was patented. Doxford's first ship, Turret, was notable for her abnormally long and wide hatches in the turret, and self-trimming due to the rounded shape in the upper hold and lower turret. She was thus ideal for grain.[6] Turret was designed for tonnage of 4,700 DWT at a load line draft of 20 feet 3 inches (6.2 m) at 2,850 GRT.[7] With engines aft the design was seen as ideal for the bulk oil trade meeting the latest Suez Canal regulations in which coal bunkers would be separated from oil cargo by a double bulkhead filled with water.[7] The ship had an unusually high righting angle which was obtained whether full or lightly loaded.[7] In particular the design was seen as a solution to the problem of strength and economical cost.[8] On well deck ships the lack of a continuous line of the deck, one the turret ship design solved with a continuous line and solid structure up to the top of the turret, resulted in weakness with classification societies taking notice by requiring increased strengthening in construction.[7][8] The long, wide hatches were seen as making the design especially suitable for carrying heavy or bulky machinery.[6] That feature later resulted in cargoes such as 75 feet (22.9 m) long, 8 feet (2.4 m) wide girders and a 110-ton gun being easily loaded.[9]
By March 1895 the design had considerable acceptance. Nine ships were in use: Turret, Turret Age, Turret Bay, Bencliff, Turret Bell, Progressist, Royalist, Hopedale and Forest Abbey; and five more were being built.[8]
Description and design
In side profile, turret deck ships resembled other merchant ships with flush decks or with small forecastles and poop decks.[10] In cross-section the differences between turret deck ships and more conventional ships are apparent. There was no gunwale; the vertical side of a turret ship curves inward above the load line to a horizontal plane. This flat area was known as the harbour deck.[11] Further inboard, this "deck" arced to the vertical again by a reverse curve. That vertical plane then joined the weather deck atop the turret at a right angle.[12] Structurally these elements were part of the hull, not of the superstructure, and the cargo holds of the ship extended up to the true weather deck atop the turret.[13]
This design, and that of its near relative the trunk deck ship,[14] were said to maximize strength, allowing larger ships and reduced the amount of steel needed for construction.[15] In reality, it is more likely that the geometry inhibited the development of cracks in the sheer strake but ships to this design were not any lighter than conventional ships due to their unique geometry. In operation their hull form promoted self-trimming of homogenous cargo and inhibited shifting.[5]
The design also called for a cellular double bottom, which was the probable reason for claims of the type's exceptional hull strength, but it also raised the
Turret deck ships had a low net tonnage (an approximate measure of cargo space) in comparison to their deadweight capacity (weight of cargo), allowing them to operate at a lower fee structure than a conventional hull. 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.[18] Turret and trunk deck ships therefore paid less in tolls than conventional ships of the same capacity.[19]
In 1911, the toll measure changed at Suez to account for all cargo spaces, and contemporaneous refinements in the design of ships of more conventional hull form eliminated the structural advantages of turret deck ships.[20] Construction of the type therefore ceased.[19]
History of use
Over 180 ships of the type had been built before the design was abandoned,
While used for general freight, these ships were particularly suited to the carriage of bulk cargos such as grains, coal, and ores.
See also
References
Notes
- ^ Craig 1980, p. 35; Woodman 2002, p. 179. Woodman identifies this vessel as the Charles H. Wetmore; named elsewhere as Charles W. Wetmore. Oakley 2005
- ^ Oakley 2005
- ^ Duerkop 2007, definition 65, Whaleback
- ^ a b Doxford Engines (archived 2/2/2007)
- ^ a b Woodman 2002, p. 179
- ^ Craig 1980, inside front cover – Different types of vessels classified in Lloyd's Register Book (illustration); Woodman 2002, p. 180 (illustration of exemplars of trunk and turret deck ships, taken from Paasch, From Keel to Mast-Truck, a marine dictionary).
- ^ An Australian's Experience, Walter Rignold Marshall (1901–1988). See section entitled Mokatam at bottom of page, with profile and accompanying text.
- ^ Craig 1980, inside back cover – illustration reproduced from Transactions of the Institute of Naval Architects, XLIX (1907)
- ^ a b c The Scanner, 1971
- ^ Trunk deck ships differed from turret ships in that the formers' sides and decks joined at right angles, rather than arcs as in turret ships. Woodman 2002, p. 180 (diagram); Craig 1980, inside front cover
- ^ a b Craig 1980, p. 35.
- ^ Woodman 2002, p. 179; Duerkop 2007, definition 62, Turret Deck Ship
- ^ a b Bax, John. "Clan Line. Part Two". Merchant Navy Officers. Archived from the original on 2009-03-29. Retrieved 2021-11-23.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - hold under the harbour decks, which were outboard of the turret. E.g., Clan Line; Duerkop 2007, definition of Turret Deck Ship. Another source states that the type "had special advantages over the Suez Canal tonnage measurements, as the hull above the harbour deck was regarded as an 'erection.'" Hardy 1924, pp. 70–71, reproduced in SS Claverly Wreck Report. This may suggest that the turret was treated as superstructure rather than hold space. In either case, part of the cargo hold was excluded from measurement.
- ^ a b c d Duerkop 2007, Some Marine Terminology (definition of Turret Deck Ship).
- ^ Craig 1980, pp. 35–37.
- ^ Clarkson, Fenton & Munro 2007, p. 38.
- ^ Turret Cape, by then renamed Walter Inkster, was still in service in 1950, departing Port Arthur, Ontario on Lake Superior in September of that year and arriving in Manitowoc, Wisconsin on Lake Michigan."Crew Lists of Vessels Arriving at Manitowoc, Wisconsin, 1925-1956" (PDF). Publication No. M-2045 (from INS records). 1996. Retrieved 15 November 2007.
- ^ "Wear Built Ships". Retrieved 27 January 2020.
Sources
- Bax, John. "Clan Line". Merchant Navy Officers. Archived from the original on 2009-03-29. Retrieved 13 November 2007.
- Clarkson, John; Fenton, Roy; Munro, Archie (2007). Clan Line Illustrated Fleet History. Preston: Ships in Focus. pp. 35–38. ISBN 978-1-901703-47-4.
- Craig, Robin (1980). Steam Tramps and Cargo Liners 1850–1950. The Ship. Vol. 5. London: National Maritime Museum / WS Cowell Ltd for ISBN 0-11-290315-0.
- Duerkop, John (July 2007). "Some Marine Terminology". Research Resources. Marine Museum of the Great Lakes at Kingston. Archived from the original on 6 July 2011. Retrieved 6 June 2014.
{{cite web}}
: CS1 maint: unfit URL (link) - "Engines". Doxford Engine Friends Association. Archived from the original on 20 December 2007. Retrieved 11 November 2007.
- Hardy, AC (1924). Merchant Ship Types: A survey of the various units engaged in the water transport of people and merchandise. London: D Van Nostrand Company. pp. 69-71.
- Marine Engineer and Naval Architect (1892). "Doxford's Patent Turret Cargo Steamer". The Marine Engineer. 14 (1 April 1892). London: 10–12. Retrieved 6 June 2015.
- Marine Engineer and Naval Architect (1895). "The "Turret" Steamships". The Marine Engineer. 16 (1 March 1895). London: 511–512. Retrieved 6 June 2015.
- Oakley, Janet (27 July 2005). "Whaleback freighter Charles W. Wetmore arrives in Everett on December 21, 1891". Essays. HistoryLink.org. Retrieved 12 November 2007.
- "SS Claverly". Wreck Reports. SouthWestMafia.com. 2007. Archived from the original on 1 October 2011. Retrieved 10 November 2007.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) - "Turret Steamers On Our Inland Seas". The Scanner. 3 (7). Toronto: Toronto Marine Historical Society. April 1971. Retrieved 10 November 2007.
- Walton, Thomas (1908). Steel Ships: Their Construction and Maintenance. London, Philadelphia: Charles Griffin & Co./Lippincott. p. 154–60. LCCN 20003198. Retrieved 5 June 2015.
- ISBN 1-58574-621-5.
Photographs
- Colour photographs of model of SS Nonsuch, a highly detailed full-hull builder's model in the collections of the National Maritime Museum. Nonsuch was built by Doxford in 1906 for Bowles Brothers and lost to air attack in 1944. "Description, Turret deck cargo ship 'Nonsuch'". Collections Online, ship models. National Maritime Museum. Archived from the original on January 27, 2006. Retrieved 6 June 2014.
{{cite web}}
: CS1 maint: unfit URL (link) - SS Claverly Wreck Report, showing a stern view of SS Claverley showing narrow harbour decks a short distance above the water. Claverley, 3,829 gross register tons (GRT), was built by Doxford in 1907, owned by Sutherland Steamship Company, and torpedoed by a German U-boat near the Eddystone in 1917. "SS Claverly". Wreck Reports. SouthWestMafia.com. 2007. Archived from the original on 1 October 2011. Retrieved 12 November 2007.
{{cite web}}
: CS1 maint: bot: original URL status unknown (link) That source also reproduces pages 70–71 of Hardy (1924), with figure 28 showing a midships cross-section of a turret vessel. - Historical Collections of the Great Lakes maintained by Bowling Green State University has some photographs of turret ships. The photograph of Turret Chief shows a heavily laden vessel with harbour decks nearly awash.