Saturday, 27 July 2013

TERROR MODIFIED: THE HISTORIC PLANS (Part 1)

As outlined in a previous post, HMS Terror, originally designed as a bomb ship, was extensively modified three times for separate polar expeditions. Like all bomb vessels, she was already  highly specialized, with an exceptionally strong frame built to withstand the punishing recoil of her two massive mortars, and a spacious hold for storing munitions (for an excellent discussion of the Terror’s original configuration, please consult Ware [1991]). To build an accurate model of the Terror as fitted for the 1845 expedition requires concatenating design information from all of the plans as well as data from other historical sources. The plans discussed here are preserved at the National Maritime Museum in Greenwich, and copies are available for purchase from their online image library. Detailed images of the plans are also presented in Ware (1991).

1812 Sheets
A full set of plans “as designed” and dated March 30th, 1812, exist for HMS Terror; these are shared with her identical sister ship HMS Beelzebub. It is important to note that HMS Vesuvius plans are virtually indistinguishable and the two sets only differ in minor details (for example the scarph joints on the keel are not depicted in the Vesuvius plans). HMS Terror was so extensively modified that its final 1845 form bore little outward resemblance to her original design. The 1812 plans are critical, however, as they are the only drawings that show her sheer, half breadth, and body plans, lines, framing configuration, keel and keelson construction, and stem and stern architecture.

1836 Sheets
HMS Terror’s first extensive modification began in 1835 and is outlined in a series of plans dated March 1836 (and later December 1837) which illustrate the inboard profile and all decks. The plans are extremely important because they illustrate the fundamental refit of the Terror - and thus represent her final overall size and shape as she appeared in 1845. The plans also document some important innovations for polar exploration that would be adopted by all subsequent polar expeditions (for an excellent overview see Battersby and Carney 2011).




1:48 scale half block model, possibly depicting HMS Terror as fitted in 1835, National Maritime Museum Collections.


Perhaps the most extensive modification shown in these documents was the creation a flush deck with two layers of three inch planking to increase strength. Though not drawn on the plans, contemporary images by Owen Stanley reveal that the copper sheathing on the Terror’s hull below the waterline was removed as protection from shipworm was not needed in the freezing waters of the Arctic. In its place, a cross-shaped series of thick copper reinforcement plates were riveted to the bow to protect against ice damage.



The ship’s profile was modified significantly as well. The stern galleries were removed (to eliminate any projection that would catch the ice), and the stern, at the position of the upper and lower decks, was both lengthened and widened, presumably to provide more space on these decks. The bow was altered as well, with the keel simplified and the ship lengthened overall. It is uncertain if the cant frames were altered or if the bow was simply bolstered behind the new copper reinforcing plates (a strong likelihood), but the plans clearly illustrate a forward change in the overall frame position.

On the interior, the Terror’s bow was reinforced with solid oak chocks bolted to the stemson, forming a solid mass of wood ranging between 4 and 8 feet thick from the wale down to the keelson. In an effort to strengthen and streamline her contours against the grasping ice, each of her chock channels were individually filled in and planked over.  Thick iron plates were added to their upper surface, and the chains were replaced with solid iron plates bolted to the planked chocks. A spare rudder was suspended in a special well just behind the mainmast which penetrated from the upper deck down to the hold.

According to the inboard profile, the Terror’s mast positions were moved forward slightly and the rake of her masts, particularly the mizzenmast, appear to have been altered. It is uncertain when these modifications occurred, but they were probably done to improve the sailing qualities of the vessel (see previous post). In fact, they might have been undertaken during extensive repairs after the Terror was nearly wrecked in Portugal in 1828.

A cistern for melting ice was added to the ship’s stove, and 47 large iron storage tanks were added to the hold for water and other provisions. A novel addition was a hot water heating system fueled by a massive furnace in the orlop deck. The system functioned by pumping warm water through a complex series of pipes into the crew’s quarters on the lower deck. The furnace was an abject failure; it never worked as designed and George Back (1838) reported that it constantly had to be dismantled and repaired:

Perhaps the most overlooked innovation instituted during the 1835 refit was a system of watertight bulkheads designed to make the ship unsinkable. The concept of airtight chambers appears to have been the invention of Sir Robert Seppings and was first implemented by Sir Edward Belcher on the HMS Aetna (Belcher 1870: 156).  As Belcher described, “the Terror was the model ship” for an entirely new coal-based bulkhead system and it was to be used by him in the abortive rescue of the stranded whalers in 1835 (see previous post). He describes the system thusly (Belcher 1870:156):


Though Back (1838) gave them no credit, the bulkheads undoubtedly helped keep the Terror afloat during her harrowing return journey across the Atlantic. As Belcher (1870:156) described:

The Naval authority must have agreed with Belcher, as the 1839 midships section and hold plan (see below) display that the bulkhead system was incorporated into the Erebus with little apparent modification. The 1839 midships section shows that the bulkheads were constructed contiguous with the frames in the hold and orlop decks and were lined with “two thickness of 1 ½ inch African [board] wrought diagonally across each other”.


 
References:

Back, George R.
1838    Narrative of an Expedition in H.M.S. Terror, Undertaken with a View to Geographical Discovery on the Arctic Shores in the Year 1836-7. John Murray, London. 

Battersby, William, and Carney, Peter
2011    Equipping HM Ships Erebus and Terror, 1845. International Journal for the History of Engineering & Technology 81(2):192-211.

Belcher, Sir Edward
1870     Admiral Belcher’s Remarks on Bulkheads. Transactions of the Institution of Naval Architects 11:155-156.

Ware, Chris.
1991     The Bomb Vessel: Shore Bombardment Ships of the Age of Sail. Naval Institute Press, Annapolis.



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