OLIVER LANG'S STERN

Oliver Lang's 1845 stern plans currently held in the National Maritime Museum's
collections. The title indicates that the plans are of HMS Erebus, but the dimensions
 of the plan, especially the height of the bulwarks, match HMS Terror plans
more precisely. Additionally, the transcribed version of these plans occur on the
1836/37 profile plans for HMS Terror, and match the 1812 plans for Terror
relatively accurately. 

In February 1845, Oliver Lang, Master Shipwright at Woolwich, faced a daunting challenge. The Admiralty, under pressure from Parry, had decided to outfit HMS Erebus and Terror for auxiliary screw propulsion, powered by small passenger locomotives.

Screw propulsion was in its infancy and contemporary designs, based on patents filed by Francis Pettit Smith and others, called for the placement of the propeller opening in the deadwood of a steam powered vessel (Bourne 1855:28). However, applying such a modification to polar vessels would critically weaken the stern, and Lang knew from the Terror’s first arctic expedition that even the most robust sternpost was severely vulnerable when overwintering in sea ice. How could he protect the ship’s stern from the pack when a gaping hole had to be cut in the deadwood for the propeller?

His solution appears in a plan dated March 17th, 1845, which was subsequently transcribed onto the 1836/37 profile plan for HMS Terror. Instead of altering the ship’s existing stern, Lang simply extended the stern of the ship aft by adding a new keel section, onto which a new rudderpost and aperture for the propeller were attached. The 1836/37 plans seem to show that Terror’s original sternpost had been modified for Back’s voyage,  but the 1845 annotations clearly indicate that Lang reconstructed it to the same configuration used in Terror’s original design (alternately, it is possible that Terror’s stern was not modified in 1836 as planned).

Lang’s 1845 design called for a triangular piece of wood to be bolted to the original sternpost, creating a vertical face for the propeller aperture. The new rudderpost and the angled fitting were both tenoned into the keel extension, as indicated by the presence of horizontal bolts on a contemporarymodel of the design. The entire structure was then bolted to a massive u-shaped “staple knee”, made from 3.5 inch thick iron, which was the same length as the propeller opening.

Lang next turned to the problem of protecting the new rudderpost and propeller aperture from ice damage. He settled on a well system which could be used to ship and unship the propeller, similar to a design patented by Joseph Taylor in 1838 (Bourne 1855:32). However, Lang’s system included a new innovation; when the propeller was unshipped, the well would be filled with a series of stacking wooden and steel chocks. The chocks were shaped to match the dimensions of the new rudderpost and deadwood and would completely fill the well, thus reinforcing the rudderpost against forces exerted by the ice.

Taylor’s patent described that the propeller could be shipped via “vertical grooves cut in the true and false stern posts … in which frame the propeller is placed” (Bourne 1855:32). However, the use of reinforcing chocks required that this system be modified. Lang replaced the grooves in the stern and false stern with robust gunmetal rails which themselves had a vertical slot running much of their length. The protruding rails were necessary to secure the chocks in the propeller well and needed to be very strong to endure the pressures of pack ice (I’ll present more on the configuration of this rail system and the propeller in a subsequent post).

While we may never know how Lang’s chock system faired after two years in the grinding pack off King William Island, we can surmise that it must have worked relatively well because the Terror survived its first winter at Beechey Island in sailing condition. Further, we know that the same chock system was installed on the Intrepid and Pioneer (Anonymous 1850:8), steam tenders used in the Franklin search effort, and that both ships survived multiple winters in sea ice before being abandoned in relatively seaworthy condition.

Scantlings for Terror’s Sternpost and Rudderpost

Sternpost

Sided:              

At Head = 13 and ½ inches 
At Heel = 10 and ¾ inches
Moulded depth = 17 and ½ inches

Rudderpost
Sided:
At Head = 13 and ½ inches
At Heel = 10 and ¾ inches
Moulded depth = 13 and ½ inches

References:

Anonymous

1850       Naval Intelligence — The Arctic Expedition. The Times.  Monday , 6^th May, pg 8.

Bourne, John

1855       A Treatise on the Screw Propeller with Various Suggestions for Improvement. Longman, Brown, Green, and Longmans, London. 

Cut stern pieces prior to assembly.

Assembled stern architecture (significant iron work has yet to be installed, and  

the temporary basswood piece is to provide rigidity until the propeller well is completed).

Detail of keel piece and opening for the staple knee. 

Aft view of the unique rudderpost joint. 

Another view of Lang's design.

Sanding two of the sternpost bolsters to match the aft station

(the bolsters provide width needed for the propeller well).

Detail after sanding. 

Comparing the sternpost bolster to the body plan.

Completed rudderpost and sternpost bolsters.

Two of the bolsters in place, showing how they add width to the stern to accommodate

the propeller well (these aren't glued and cannot be until the bulkhead is attached). 

Current progress on the stern, keel, and stem.