Monday, 29 June 2015

PULLING A RABBET FROM TERROR’S HAT

Last month, I finished the most angst-ridden part of my project to date - cutting two seemingly miniscule 1.5 mm wide grooves along the length of the keel and stem of my model. These v-shaped notches, known as rabbets, provide a seat for the edges of the hull planking where they meet the centreline timbers of the ship. On a plank and bulkhead model, it represents a critical reference point around which the hull architecture is based.  

My trepidation was rooted in the fact that the rabbet position isn’t shown in Terror’s 1836 draughts [1] (the 1839 draughts [2] only show the rabbet position for Erebus). Normally this wouldn’t be an issue, as Terror’s 1812 [3] profile plan clearly shows the position of the rabbet. However, the 1836 plans show that Terror’s bow, and in particular her upper deck and bulwarks, were extended forward approximately 12.5 inches (why this was necessary is still a mystery to me). This implied that her rabbet position must have been moved forward as well, to accommodate a smooth run of planking along the bow.

The rabbet carved into the model’s keel. Like the merchant ships which were the basis for Terror’s 
design, the 1812 draught shows the rabbet was taken out of the centre of the keel 
(incidentally, this position probably contributed to her poor sailing qualities).

I had originally assumed that Terror’s cant frames, hawse pieces, and bollard timbers may have been modified to accommodate this lengthening of the deck. This wasn’t an unwarranted assumption, because Terror’s 1836 profile plan shows that Terror’s upper stem piece was extensively remodeled, suggesting a significant refit of the bow timbers.

However, after further consideration, I’ve come to the conclusion that such extensive modifications were very unlikely. We know that Terror’s original top-timbers and bulwarks were entirely levelled when she was caught in a hurricane near Lisbon in 1828 [4]. This means that replacement bulwark stanchions needed to be installed when the ship was repaired. The upper deck may have been expanded at this time, but I suspect this occurred in the 1836 refit as the solid chock channels provided an opportunity (and platform) to most effectively hide this shift forward. In either case, because her bulwarks had been levelled, the modifications could have been made without extensive reworking of the bow timbers.

Therefore, my solution is to leave the rabbet position precisely as shown in Terror’s original 1812 draughts and to rely on modified bulwark stanchions to account for the lengthened deck. This permits me to move forward with the project with the least amount of conjecture, because the only speculation I need to make is about the construction of the most forward bulwark stanchions.

The port stem rabbet .

Another view of the rabbet - note how it "opens" slightly closer to the heel of
the stempost. 

A dummy section of planking dry-fitted into the rabbet, showing how it interacts
 with one of the station bulkheads. 

Settling on a final position of the rabbet allows me to finally assemble the bulkheads and begin planking the model. This decision also permitted me to finally draft a plan of Terror’s complete bow architecture.



Profile of the Terror’s bow architecture, showing the manner the bow was
strengthened for polar exploration service. To accommodate the
lengthening of the deck, I added a conjectural 12 inch chock fayed to
the fore edge of the bollard timbers and cant frames, against which
the bulwark stanchions would have been bolted.


Plan of Terror’s lower deck, detailing the layers of planking and
metal sheathing added to the ship

The plans expose the effort the Admiralty placed on strengthening the ship’s bow at the waterline. More than 55 inches (4.5 feet) of iron reinforced oak separated the stores on Terror’s orlop deck from the water. Near the foremast step, that distance multiplied to nearly 12 linear feet. James Clark Ross [5] tested these reinforcements in a most daring fashion during his Antarctic Expedition. By January 5th, 1841, Ross had spotted what he thought was open water south of the Ross Sea but found his way to it blocked by a ring of thick pack ice. Confident in his ships, he sailed along the barrier until he saw a “favourable point” and, under sail, rammed the Erebus and Terror into it for an hour, eventually fracturing the ice and punching his way through. He discovered the Ross Ice Shelf six days later.   


Footnotes:
[1] National Maritime Museum Object ID: ZAZ5672, ZAZ5663

[2] National Maritime Museum Object ID: ZAZ5673

[3] National Maritime Museum Object ID: ZAZ5615

[4] 1835. Narrative of the Wreck of H.M.S. Terror. United Service Journal and Naval and Military Magazine 1. Pages 229-236.


[5] Ross, Sir James Clark. 1847a. A Voyage of Discovery and Research in the Southern and Antarctic Regions, During the Years 1839-1843: Volume I. John Murray, London. Page 176.

2 comments:

  1. Nice Website...
    Hey JOIN now fblikesbot.com and Increase Facebook Likes your profile and websites.
    Increase Facebook Likes and check your website worth worth my websites
    FB Likes and check your website worth Website Value Calculator
    Hot Wallpapers
    its may be very beneficial for you also really

    ReplyDelete
  2. This article is said with what I’m worried with and http://awriter.org/ninjaessays-com-review/ it is fantastically manufactured.

    ReplyDelete