Onrust Dock of 3,000 tons

At first Onrust Dock of 3,000 tons was mostly known as 'the iron dry dock', because there was only one iron dry dock in the Dutch East Indies. It was destined for Onrust Island, which housed one of the two naval bases in the Dutch East Indies. Previously there had been a wooden dry dock at Onrust Island. When the iron drydock arrived at Onrust, it was designated as Onrust Iron Dock, or Iron Dock of Onrust. Later, another iron dry dock was sent to Onrust Island. This necessitated the designation of our drydock by its lift capacity of 3,000 tons, and eliminated the need for the label 'iron'. When the location of the dock changed, so did that part of the name. In the end it was referred to as Sabang Dock of 3,000 tons, but also as 'the 3,000 tons dock', or 'the small dock at Sabang'.

Dry dock capacity had become very important with the introduction of the screw propelled ship. Traditional methods for maintaining ships required them to be put on shore. This was very dangerous for screw propelled ships, as the slightest deformation of the hull could block the screw axle. Meanwhile, screw propelled ships needed regular inspection. In a dry dock a screw ship rested on its keel. The risk to the hull was minimal, and an inspection could be done in a day.

Before its construction, in the 1850s, there were two wooden floating docks in the Dutch East Indies. Due to the increased demand the admiralty in the Dutch East Indies wanted to have a third, bigger floating dock. It foresaw that during the scheduled maintenance and repairs of the docks themselves, the remaining dock would not provide enough dry dock capacity. Furthermore, the existing dry docks were not capable to receive the biggest ships.^[1] The wooden dock at Surabaya handled the Groningen-class corvettes of 1,780 tons with great difficulty. The wooden dock at Onrust was longer, but still not long enough, and was not capable to receive loaded ships.^[2]

Due to the known condition of the grounds at the naval base Onrust near Batavia, and the experience gained in the attempt to construct a fixed dry dock at Onrust, the East Indies Authorities decided that a floating dry dock was required. The only doubt was whether it should be made of wood or iron. The decision to opt for an iron drydock was made in part because iron floating docks had already been made in the United Kingdom. Rennie and Sons in London had made an iron dry dock for the Spanish navy. Randolph, Elder & Co. had made an iron floating dock for the French navy at Saigon and an iron dry dock for Cores de Vries on Java.^[2]

The authorities in the Dutch East Indies sent a design of the floating dry dock it required to the Netherlands. This was received in spring 1860.^[3] This was the original design by C. Scheffer,^[4] then a Navy engineer in Surabaya.^[5] The East Indies authorities also proposed to place the order at Van Vlissingen en Dudok van Heel. The minister of the Colonies and the minister for the Navy thought differently. They decided that August Elize Tromp and J. Strootman (who wrote the article in the reference section) would make a revised plan. In 1862 they would visit England for that purpose.^[2] In the end the revised design was very close to the original design.^[6]

The ministers for the navy and the Colonies decided to have a public tender. In mid-December 1862 the tender for the dry dock was announced by the minister of the navy Willem Huyssen van Kattendijke.^[7] On 3 February 1863, the public tender for the iron dock in the East Indies was held. The list of 17 contestants reads like a who's who of Dutch industry at the time. Van Vlissingen en Dudok van Heel was the cheapest at 366,685 guilders.^[2] Of the other offers that by Randolf Elder from Glasgow was highest at 695,700.^[8][9] The contract was approved on 5 March 1863.^[10]

Van Vlissingen en Dudok van Heel would not build the drydock on one of her slipways. Instead it had a terrain between the boiler factory and the warehouses for the shipyard. There the bottom ash produced by the factory had been dumped for years, and consisted of a layer of about 2 m deep. With quite some effort it was made into a solid level underground to support the dock. Even so, part of it would sag a bit. The terrain was surrounded by a railroad with turntables, that led to the workshops. Most of the iron was delivered by Société des hauts-fourneaux, usines et charbonnages de Marcinelle et Couillet. Mr. B. van der Linde was the overseer of construction.^[2]

In Amsterdam the dock would be constructed, but not entirely riveted. It would then be taken apart again and be assembled in Surabaya. Readying the construction site, and getting the iron took quite some time, and it was almost May before good progress was made. On 7 April 1864 Prince Napoléon Bonaparte visited the shipyard of Van Vlissingen en Dudok van Heel, and especially the iron floating drydock under construction.^[11] On 9 June 1864 some members of the Royal Institute of Engineers visited the floating dock after attending their annual meeting. Van Vlissingen en Dudok van Heel made pictures and sent them to the members of the institute.^[12] The final cost of the floating dock would be 460,852 guilders, of those 41,018 were for transport.^[10]

In June 1864 the first one third extremity of the dock was taken apart, and in late July 1864 loading was started.^[10] On 28 September 1864 the ships Regina Maris of Captain S. Ouwehand and Nederland of captain van A.A. van Steenderen left Texel for Surabaya carrying this part. The other extremity of the dock was loaded on Nieuwe Waterweg of captain E. von Lindern, while she was in Rotterdam. On 28 October 1864 she left from Brouwershaven. C. September 1864 the center of the dry dock was taken apart. This part would be sent on board Wilhelmina of Captain J. Snoek which would also be loaded in Rotterdam. Loading started in November, but soon ice blocked the inland canals, and so loading took till early February 1865. On 4 February 1865 Wilhelmina left Rotterdam under Captain H.J. Brauer. The Petronella would transport a final shipment of rivets.

On 15 January 1865 Nederland arrived in Surabaya with 1,687 pieces of iron.^[13] On 24 January Regina Maris arrived. Their cargo consisted of 498,000 of sheet iron, 91,200 kg of angle- and T-Iron bars up to 13 m long, 165,000 kg of frames and 45,800 kg of rivets.^[14] On 9 February 1865 Nieuwe Waterweg arrived in Surabaya with a comparable cargo.^[15] On 27 May 1865 Wilhelmina of Captain H.J. Brauer arrived in Surabaya.^[16]

Meanwhile, in Surabaya, preparations had been made to create a place were the drydock could be assembled. On 9 January 1864 a tender was held to create a suitable terrain for assembly in Surabaya. The terrain (called 'dock pit') was to be surrounded by dykes and have a number of warehouses.^[17] In Surabaya Mr. B. van der Linde was again overseer for assembly.^[18]

After the first shipments had arrived assembly of Onrust Dock of 3,000 tons could start. On 3 April 1865 the first parts of the 'pontoon' were assembled. The idea was that as soon as the 'pontoon' was finished, it would be brought to deeper water, where the higher parts would be assembled.^[12] It would take over four years before the pontoon left the dock pit and entered the basin (the harbor of Surabaya). This happened at spring tide on 26 May 1869.^[19]

It was customary that a shipyard offered a model of the ship to the principal.^[20] In the case of the drydock this was a rather lavish brass model. It represents one-half of two-thirds of the length, complete with steam engine, pumps, piping, sluices and valves. It is a piece of high-quality workmanship, executed in great detail, with sections of walls that open and shut to reveal the interior. The entire construction has been followed accurately: all the frames and bulkheads have been fitted, even in the parts that do not open and are inaccessible to the eye. Not all the rivets have been clinched, though thousands of tiny holes have been drilled through the brass sheets and frames. The model likely approaches the condition of the dock when it was temporarily assembled in Amsterdam rather than the finished product in the East Indies.^[21]

In 1867 the model was in the Dutch section of the International Exposition in Paris. The famous writer Vice Admiral Edmond Pâris thought the Dutch section the most interesting of those of the maritime nations after that of the United Kingdom and France.^[22] The model of HNLMS Adolf van Nassau (1861) drew his attention, and so did the model of the clipper Nestor launched by Smit Kinderdijk in 1866. The model of Onrust Dock of 3,000 tons was the largest piece of the Dutch section, but was only briefly mentioned by him.^[22] Others thought the Dutch part of the exhibition was not interesting except for the part about drydocks.^[23] The model became part of the model collection of the navy, that is now part of the Rijksmuseum. It had been in storage there since 1925, when in the 1990s it was decided that it should be part of the permanent exposition, and was restored to its former splendor.^[23]

The floating dock was 90 m long, with a beam of 24 m and a height of 10.55 m. The depth of hold was given as 8.05 m 'on the iron upper or dock floor', which is a strange definition of hold. On the inside the dock was smallest at the floor, with a width of 12.30 m. On top it had a maximum width of 21 m. The bottom of the dry dock was a kind of pontoon. This pontoon had three longitudinal bulkheads and six transverse bulkheads, dividing it in 28 compartments. Thickness of these bulkheads was 10–13 mm.^[2] The weight of the dock was 2,126,472 kg

The water would be pumped out of the pontoon by two steam engines situated at the height of the second walkway. These were high pressure steam engines of 20 nominal hp. The cylinder had a diameter of 45 cm and a stroke of 36 cm with a pressure of 2.5-3 atm. Two belt pulleys of 1.62 m diameter drove two Gwynnes centrifugal pumps. Together these four pumps had to pump out 6,000 m3 of water in two hours in order to completely raise the dock. A system of tubes and valves made it possible to regulate the amount of water that remained in each compartment. This was especially important when shorter ships were docked. By leaving more water in the compartments that were not 'under' the ship, less strain was put on the dock.^[24]

According to the plan Onrust Dock of 3,000 tons would be able to lift a fully loaded screw frigate, weighing 3,000 tonnes.^[10] The units that fitted this description were the largest ships of the Dutch navy. These screw frigates were not permanently stationed in the east, but could be deployed there, and so a repair facility was required. The question is whether the Adolf van Nassau of 3,750 displacement could be lifted by the dock.

When construction started, Onrust Dock of 3,000 tons was one of the first floating dry docks. As such she had a few particularities. On the inside she was still shaped like a ship, as were traditional dry docks on land. Newer dry docks would soon abandon this shape. She was made in one piece. Newer dry docks would soon be made of connecting pontoons. The big advantage was that this made them 'self docking', because they could dock their own parts. Onrust Dock of 3,000 tons could not, and so the big question was: Where would the dry dock dock? Another development was that soon most dry docks would shift to electrical power, and would get it from shore.