Tuesday, 13 August 2013

DESIGN INFERENCES

A significant quantity of historic source material, including original Royal Navy plans, exploration accounts, news reports, and personal letters, sketches, and drawings exist which document the final 1845 configuration of HMS Terror. Creating an accurate plan for the ship requires carefully parsing these data and drawing inferences about the ship’s probable appearance. Below, I outline the rationale behind my reconstruction of major aspects of the Terror’s final 1845 design, as fitted. This is not an exhaustive account, and specific topics such as the locomotive engines, funnel and chimney sizes and positions, propellers, cipher and name, and paint scheme will be discussed in later posts.

Bow/Stern Shape:
As described previously, the 1839 plans depict HMS Erebus, and therefore the 1836 profile must provide the basis for the bow design of the Terror, which is substantially different from the 1813 profile. It is uncertain if the 1836 refit resulted in modification of the cant frames, but Rice (Ross 1847a) appears to indicate that bolsters were added to the exterior of the frames to change the line of the bow.



In my plans, the stern configuration and framing is exactly as depicted in the 1845 annotations (in green ink) of the 1836 profile, which were made to accommodate the auxiliary screw propeller.  

Keel, False Keel, and Stem:
The position and configuration of the keel is based on the 1813 inboard profile. The stempost configuration is based in the 1836 inboard profile, but lengthened slightly to accommodate the new position of the bowsprit as shown in the 1845 alterations (in green ink). I should note that a faint pencil modification in the 1813 inboard profile of HMS Vesuvius also appears to depict the outline of the stempost as drawn in the 1836 Terror profile. The scarph joints on the stempost are based on the 1813 profile, or based on standard designs for the era (e.g. Goodwin 1987:29).

Keelson and Stemson:
The keelson and stemson designs are based on the 1813 profile, but with alterations at the stern to be consistent with the 1845 annotation (in green ink) of the 1836 inboard profile. The bolstering and riders added above the stemson are based on the 1836 inboard profile plans.
 

Deadwood, Rising Wood, and Knee:
The bow and stern deadwood configurations are not documented in any of the Admiralty plans. Interestingly, the 1813 plans indicate that HMS Terror utilized an older stemson design than the era in which it was built; therefore, the in my plans the deadwood configuration is based on a style in use ca. 1800 (Goodwin 1987:29). The rising wood configuration at the bow is based on the 1813 profile which is partially complete, with information drawn from standard styles utilized in the early 19th century (Goodwin 1987:29). The knee of the Terror was essentially removed (as discussed by Rice [Ross 1847a]), and was replaced with a highly reduced and simplified knee that projected only enough to support the bowsprit. The knee configuration in my plans is based on the 1836 profile, lengthened to support the new position of the bowsprit as depicted in the 1845 annotations on that plan. The joints for the knee (i.e. the configuration of the gripe and bobstay pieces) are based on standard conventions for the period (e.g. Goodwin 1987:37).


Rabbet Line:

Because of the lengthening of the bow and the reduction in the knee, the Terror’s rabbet line must have been highly unusual. The model of HMS Erebus at the National Maritime Museum indicates that the knee (much of which was covered in plating) was essentially flush with the hull planking at the bow.  No rabbet is depicted in the 1836 plans of the Terror, so at the bow I based in on the on the thickness of planking as depicted in the 1839 midships section, with the goal of keeping the hull planking below the chock channels (and excluding the wale) flush with the knee. Closer to the keel, the rabbet line recedes until to meets the original rabbet line depicted in the 1813 profile. The rabbet on the keel is based on the line depicted in the 1813 profile.  The rabbet at the stern was easily deduced from the 1845 plan of the modified stern, which clearly displays where the hull planking terminates.


Bow Plating:
The position and size of the iron bow plating are based on the 1845 annotation (in green ink) on the 1836 profile. This annotation indicates that iron plating was more extensive than the cross-shaped copper plating used for the 1836 Back Expedition, but did not extend along the waterline like the copper plating utilized for the Antarctic Expedition (depicted in the 1839 profile).

Deck Fittings:
All deck fittings for my plans are based on the 1839 inboard profile of the Terror and Erebus (see a previous post for the discussion of the Royal Navy’s policy of identically outfitting exploration vessels). As discussed previously, the 1839 plans depict the Erebus, so the positioning of the furniture, masts, and other deck fittings are based on the 1836 Terror profile. The position and size of the ship’s boats are based on the 1839 plans (Terror’s boat positions are depicted in red ink), with slight modifications to accommodate the different positions of deck fittings on HMS Terror.
 
Deck Placement and Wall Partitions:
The 1845 annotations (in green ink) of the 1836 Terror profile appear to contain errors. Specifically, the placement of the decks match the 1845 stern modification plans perfectly, but do not match the position of the decks in the 1836 inboard profile. However, the drawn position of the walls and deck partitions of the 1845 modifications (in green ink) do match the 1836 and 1813 plans precisely, or make logical accommodations for new equipment (e.g. the locomotive). This would suggest that the 1845 annotations based on the stern redesign were simply copied to the plans and not specifically adapted for HMS Terror. Thus, in my plans the position the wall partitions correspond with the 1845 annotations and unmodified 1836 plans, but the position of the decks are depicted as in the 1836 plans. The construction of the upper decks (doubling) corresponds to the 1839 and 1836 inboard profiles.  
 
Bulwarks:
All the plans are inconsistent regarding the height of the Terror’s bulwarks. As described in a previous post, the 1839 Inboard profile is obviously meant to depict the Erebus (the bulwarks would be over ten feet high if placed in this position on the Terror). The 1845 annotations (in green ink) on the 1836 inboard profile likely reflect the proper position at the stern, but do not extend all the way to the bow and appear to be drawn at an inappropriate angle (possibly because it was directly copied from the 1845 stern modifications). To rectify this issue, I traced the cap rail of the 1836 plans and then raised it into position to match the stern location of the cap rail depicted in the 1845 modifications (in green ink). The bulwark lines were then extended at the bow to intersect this new cap rail position. Interestingly, this new position appears to match a pencil line marked on the plan of HMS Vesuvius. This, combined with the annotations to the stempost, strongly suggests that the pencil lines on HMS Vesuvius plans were meant to depict modifications to HMS Terror. This makes some sense; by 1845 the 1836 Terror profile was so densely annotated that that a new sheet may have been required (HMS Vesuvius was identical to HMS Terror and HMS Beelzebub).

Rudder:
The internal construction of the rudder is based on the 1836 profile, but its size, shape, position, and hardware are based on the 1845 stern plans and the corresponding annotations on the 1836 plans (in green ink).
 
Solid Chock Channels:
The 1836 plans for HMS Terror show a large gap, roughly amidships, in the solid chock channels, and this is confirmed by contemporary paintings by Owen Stanley. As described by Rice (Ross 1847a), in 1839 continuous solid chock channels were constructed on both Erebus and Terror and are shown in the 1839 profiles and deck plans representing both ships. All contemporary 1845 paintings/drawings of the Terror depict solid chock channels surrounding the ship; therefore, a solid chock channel consistent with the 1839 profile is utilized for my plans.
 
Mast Positions and Rake:
The mast position and rake are based on the 1836 inboard profile (which, as described previously, differs from the 1813 profile). Configurations of the mast steps and their method of attachment are based on the 1813 plans (mizzenmast) and 1836 plans (foremast and mainmast), but the taper of the masts (not depicted in either the 1813 of 1836 plans) is based on the 1839 plans. 
 
Windows:
HMS Terror was originally designed with five stern windows, and drawings by Own Stanley made during Back’s 1836 voyage indicate that each had six panes.



However, the central window was removed during the 1845 refit to make room for the new propeller well and the new rudder position, a modification corroborated by the drawings of Stanely, Gore, and others.



Owen Stanley 1845 "Parting company with Terror, 4 June 1845", Courtesy National Library of Australia

An engraving of Franklin’s cabin published in 1845 by the Illustrated London News shows that the windows each had four large panes (probably double-paned) with very robust sills and muntins.


Planks:
As the 1839 midships cross section indicates, the hull planks range in width from 8 inches on most areas of the hull to more than 10 inches (average) at the wales. This is corroborated by the 1845 stern plan which depicts hull planking averaging about 9 inches in width. However, it should be noted that the 1845 stern plan displays that the planks were carefully spiled with no drop planks, so it can be expected that plank widths would vary significantly beyond the average width. In my plans of HMS Terror, all hull planks aim for an average width of ca. 9 inches. The wale planks have a maximum width of ca. 14 inches at the touch, narrowing to ca. 7 inches at the butts. The wale planks are based on the hook and butt design used for bomb vessels as depicted by Goodwin (1989), a planking system which was also commonly used on polar exploration vessels and other sturdy craft (Ware 1991).


References:
Goodwin, Peter
1987    The Construction and Fitting of the Sailing Man of War. Conway Maritime Press, London.

1989    The Bomb Vessel Granado 1742. Naval Institute Press, Annapolis.

Ross, Sir James Clark
1847    A Voyage of Discovery and Research in the Southern and Antarctic Regions, During the Years 1839-1843: Volume I. John Murray, London.
 
Ware, Chris.
1991    The Bomb Vessel: Shore Bombardment Ships of the Age of Sail. Naval Institute Press, Annapolis.
 
 
 

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