The TID project

In 1942, the Admiralty realised that a large batch of tugs would be needed, to avoid the need to requisition similar vessels from existing users. They also wanted to keep the slipways at yards which were better suited to building larger ships clear of small-scale projects. The brief that they issued was "to design, organise and start work immediately, towards achieving, in the shortest possible time, delivery of one tug per week using within the process, little or no shipyard labour." Dunston's were awarded the initial contract, because they had pioneered the use of electric arc welding of hulls, a process which was much quicker and less labour-intensive than using rivetting. The ships would be constructed from pre-fabricated sections, a method used in the United States for the production of Liberty ships.^[12]

The design was for a ship 65 feet (20 m) long by 17 feet (5.2 m) wide, which was split vertically into eight sections, with unit No.1 at the stern proceeding forwards to unit No.8 at the bow. Each section would be a maximum of 10 feet (3.0 m) long and 13 feet (4.0 m) deep with a maximum weight of six tons, allowing them to be transported to the shipyard by road from the locations at which they were built. None of the frames were bent, and where the hull plates needed to be curved, the curve was in one dimension only. The joints between plates on any one unit were left unwelded for 10 inches (25 cm) at the outer edges, so that if any deviation from the designed profile occurred, the plates could be sprung together,^[13] but because each section was made using jigs, alignment issues did not occur.^[14]

Despite the angular design of the flat plates, trials using models in a test tank at Teddington showed that the resistance of the TID design was less than that of a conventionally profiled tug of a similar size up to 7.5 knots, but that at higher speeds, the conventional model was more efficient. As the design speed was 8.5 knots, this was not thought to be a serious consideration.^[15] Because the sections were to be produced by engineering companies with no knowledge of shipbuilding, Dunston's produced over 1,400 drawings covering every detail, much of which was normally omitted from conventional shipyard drawings. The frames for the vessels were placed at 21-inch (53 cm) centres, and the drawings included full dimensions at every frame. All joints between adjacent sections were made half way between two frames, and again, detailed dimensions of the outer edges were provided.^[14]

Initially, Dunston's used four fabricators to manufacture the sections, but this was soon increased to 13, and to minimise the effects of disruption on the supply of sections, each section was made by two fabricators. The fabricators involved were Robert Jenkins and Co Ltd of Rotherham (S1); Foster, Yates and Thom Ltd of Blackburn (S1 and S2); A J Riley and Son Ltd of Manchester (S2); Nortons (Tividale) Ltd of Tipton (S3); Robert Dempster and Sons Ltd of Elland (S3 and S4); Wrights Forge and Engineering Co Ltd of Dudley (S4); John Booth and Sons (Bolton) Ltd of Bolton (S5); Newton Chambers and Co Ltd of Thorncliffe, Sheffield (S5); Head, Wrightson and Co Ltd of Stockton on Tees (S6); Charles Roberts and Co Ltd of Wakefield (S6); C and W Walker Ltd of Donnington, Wellington (S7); William Neill and Sons Ltd of St Helens (S7 and S8); and Orthostyle Ltd of Ashby, Scunthorpe (S8).^[16] The sections were too large to be transported to Thorne by rail, and were therefore moved by road, despite the width exceeding the maximum permissible width of 7.5 feet (2.3 m) for road vehicles at the time.^[17]

At the Throne yard, the sections were unloaded using a hand-operated gantry. When a complete set us sections was available, they were moved to the construction area, and placed on carefully placed keel blocks, which remained in position for the duration of the project.^[18] It proved easy to produce a hull in seven days, and Dunston's created a second construction berth, allowing two ships per week to be launched.^[19] As experience was gained, a hull could be produced in five days, and some were completed in only four days. The ships were fitted with a two-cylinder steam engine powered by a vertical boiler and developing 220 hp (160 kW). These were supplied by eleven different manufacturers,^[17] and were fitted at Dunston's Hessle yard. The first hull to be launched was towed from Thorne to Hessle, where the engine and boiler were fitted. In order to test its operation, a voyage back to Thorne was made, from where it towed the next hull to Hessle before final delivery. This process was then repeated for each subsequent vessel.^[13] The initial order was for twelve tugs, but as the concept proved successful, this was increased to 25, then 50 and then 100. All were ordered as coal burners, although ten of them were changed to use oil, for possible use in the Mediterranean and the Far East. A further batch of 50 oil burners were ordered, and finally a batch of 32 oil burners which were adapted for tropical service.^[20] Of this last batch, two were built at Thorne,^[7] seven at Hessle,^[21] and 23 were built by Wm Pickersgill and Sons Ltd at their Sunderland yard.^[22]

Other prefabricated designs

Following the success of building prefabricated TID tugs, a similar approach was used to construct a number of small coastal tankers. These were built in anticipation of the D–day invasion of France. The design process involved selecting a prototype ship, 148 by 27 feet (45.1 by 8.2 m), and using it to create a straight-line design for a type of ship known as a Channel Tanker, which became known as a CHANT. After testing of a model in a tank, minor changes to the shape of the bow were made, and an aerofoil-shaped fin was added to the stern, similar to that used on the tugs. Apart from the fin, all of the plates used in the construction were flat or only rolled in a single direction, and none of the frames were bent. Individual sections were either 10 feet (3.0 m) or 20 feet (6.1 m) long, and no section exceeded 13 tons in weight. The sections were delivered to the shipyards by road, where they were welded together. To aid alignment, the seams were not welded for the final 10 inches (25 cm) where they would butt onto an adjacent section.^[23]

The design included a double-skinned hull, to reduce the risk of leakage of petroleum spirit, as they were intended to land on flat beaches. Dunston's yard at Hessle was one of five which manufactured a total of 43 CHANT tankers between February and July 1944. They completed 12, and although their original order was for 24, the success of the D–day operation and the laying of pipelines to carry fuel from England to France, known as PLUTO, resulted in there being less need for tankers. Consequently the final 12 were redesigned to become dry cargo carriers, known as the 'Empire F' class,^[23]

A total of 25 prefabricated 'Empire F' class coasters were built instead of CHANT tankers, 12 at Dunston's yard at Hessle and 13 by Goole Shipbuilding and Engineering. They were made from 28 prefabricated sections, and the ship that was originally to have been CHANT 14 was to become 'Fabric 14', but by the time of launch was known as Empire Fabric. All of the ships used the 'Empire' prefix, and a name beginning with 'F'. The CHANT and Empire F ships were built on slipways, where cranes were available, and so assembling the sections was more straightforward than for the tugs. The tankers were fitted with 220/270 hp oil engines, enabling them to travel at 7.5 knots, which was considered adequate for short journeys across the English Channel to French beaches. Slightly larger 300 hp engines were fitted in the dry cargo coasters, giving them a cruising speed of 8 knots.^[24]

During 1945, Dunston's built eleven prefabricated 'Shelt' class coasters, which were similar to the 'Empire F' class, but had shelter decks, as they were intended for use in the Far East. Another eleven 'Shelt' coasters were constructed by Goole Shipbuilding and Repairing. Many were operated by Singapore Straits Steamship Company, later Straits Steamship Company, on behalf of the Ministry of War Transport. In 1946 they bought 16 of the vessels which they had been operating, and subsequently obtained two more.^[25]

Hessle

Sources: Ships Photos^[39] and Historic Ships Register^[40]

Thorne

Sources: Historic Ships Register^[67] and Taylor 2009.