I haven't posted an update regarding my model in several
months. While I've kept busy with side projects, the real reason for my delay
is that I had reached an impasse with Terror’s stern.
As I've discussed in previous posts, the sterns of Franklin’s
ships were modified in 1845 to accommodate a new auxiliary screw propulsion
system – to be used as a time saving device “providing the wind should prove
contrary or a dead calm” . There are two sources of data on these
modifications: Oliver Lang’s original design plan , and its counterpart, a
contemporary model of the design . I had purchased full resolution copies of
the plan many months ago, but unfortunately Lang did not include a cross
section in his draught. That information could only be gleaned from the contemporary
model held at the National Maritime Museum’s storage facility in Chatham.
Fortunately, I recently had an opportunity to visit the Chatham
model ship facility. Assisted by the expert curators, I was able to study the
stern model in detail. It is quite unique, being constructed using a series of carved
blocks arranged to conform to the position of major structural and engineering
elements of Lang’s design. The information I gathered has allowed me to
complete my construction of the stern; below,
I’ll reveal the new information I've learned from the contemporary model, while
documenting my final assembly of Terror’s stern:
1) The propeller well used to raise and lower the screw was rectangular,
almost square-sided, with the sternpost and rudderpost forming the fore and aft
sides of the well, respectively. To accomplish this, thick timbers were bolted
to the sides of the rudderpost and sternpost . The rudderpost bolsters were much
more complex than I originally assumed and were each constructed of at least
two pieces, with the lower portions tapering gently to the width of the rudderpost,
following the lines of the body plan (see here for my original conceptualization of the design
|The stern pieces prior to assembly. The bolster on the left is the old design I intended to use, which was incorrect. |
|The overkill method I used to glue the bolsters to the stern and rudderposts. Thankfully this was just a dry-run|
(note the older bolster design).
|The new bolster timbers glued on the rudderpost. Note the groove for the "Lihou" rudder on the|
rudderpost. I may need to sand the bolsters somewhat to match the run of the planking as they
may be slightly oversized - but no by much.
|Another angle showing the bolster timbers on the sternpost. The NMM model shows that the bolsters on the|
rudderpost are longer than those on the sternpost.
2) The rudderpost and sternpost were each tenoned into the keel
extension, as was typical, but each was secured with a single bolt, which was
not indicated on Lang’s plan.
|Marking the precise position of the tenon bolts. |
|The bolts were simulated with 20 gauge copper wire, precisely the same as that used on the keel scarphs. |
3) The propeller well was framed on the port and starboard
sides in three distinct sections. The upper section included stout rectangular
framing fayed to the deck beams, which formed a ledge for a scuttle on the
upper deck. Below this, the well was probably enclosed by watertight planking
down to the height of the stern timbers. Because of the construction of the contemporary NMM model, such planking was not shown, but it is unlikely that solid timber pieces
would have been used, as these aren’t shown in contemporary
|The heavy framing used to form the top of the propeller well. The upper part of these timbers formed a lip|
for a scuttle to the well.
|Planking on the upper section of the well. I've estimated a width of 12 inches. The actual width is unknown.|
Note that this section of the model will be covered so I haven't simulated bolts or spikes here.
|A view of the topside of the well. The upper pieces of the sternpost and rudderpost bolsters will be|
trimmed at a later stage of the build , but are useful for alignment at this stage.
4) A new section,
clearly visible in the well of the model, started at the position of the stern
timbers. This suggests the stern timbers were bolted to the sides of the
rudderpost and sternposts to provide major structural support to the new
rudderpost and well. This makes good sense, and Lang’s 1845 stern plan clearly
shows the stern timbers as a major element of the design. In fact, these new
timbers are substantially more robust than Terror’s original stern timbers,
suggesting they were an integral part of the strength of the new structure.
Again, this type of structure is supported by contemporary
|The bottom portion of the framing planks were trimmed to match the run of the stern timbers. Note|
the rabbet on the rudderpost on the right.
5) The lower section of the propeller well was composed of the
second layer of hull planking where it ran aft, horizontally. Eventually,
the run of the higher planks would have veered away from the straight-sided
wall of the well. At this point, straight horizontal planking would have been
used to frame the sides of the well. The position where this occurs is marked
by a block seam on the contemporary NMM model.
Unfortunately, Lang’s contemporary model does not include any of
the ironwork used to strengthen the stern, nor does it include the propeller
rail/track mechanism. I've based these portions of the model on Lang’s plans
and extensive research on other contemporary models and designs. This research is
outlined in several blog posts
, and here
|The iron staple knee glued in place. The knee provided essential support for the rudderpost. |
|Mini-Crozier inspects the staple knee in dry dock. |
|Lang used iron strapping to further reinforce the stern structure. Here they are made from chemically blackened copper. |
|Each strap was glued in place and then the bolt holes were drilled out by hand. |
No matter how vulnerable it made the ship, we can suspect that Lang’s radical redesign also altered the sailing qualities of Terror. Contemporary sailing
reports indicate that Vesuvius class bomb vessels were rather lumbering and
could not carry sail well, and Ross reported that Terror was constantly falling
behind Erebus during his Antarctic voyage, delaying and endangering the expedition.
Recently, Regina Koellner, assisted by William Battersby,
transcribed a letter  from Francis Crozier to his friend John Henderson, written
shortly after the ships arrived at Whalefish Islands in Greenland. In the
letter, Crozier provides a brief report of Terror’s sailing qualities: "Our
steering is decidedly improved by the alterations on the counter we now sail
much more evenly with Erebus which is advantageous to us in many ways.
suspect that the effective lengthening of the keel to accommodate the propeller allowed Terror to sail closer
to the wind, finally permitting her to keep up with the more nimble Erebus. It
seems the final conversion of Terror to screw propulsion made her a more
capable vessel under sail, an irony certainly not lost on Crozier.
I sincerely thank Regina Koellner for permitting me to post the transcription from her recent research, and William Battersby for alerting me to this exciting primary report on Terror’s sailing qualities.
 Filling frames, similar to fashion pieces, appear to
have been fayed to these bolster timbers on the sternpost to accommodate the smooth run of planking
over the upper part of the well. My belief is that space between these frames
and behind the transom pieces was filled in with chocks, similar to the bow, to
add more strength to the stern.
 Admiralty Digest, cited from 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.
This comment has been removed by the author.ReplyDelete
Wonderfully absorbing explanations and images! I especially like the bit on sailing qualities.ReplyDelete
Thank you Glenn!ReplyDelete
What would have been the way to hook up the propeller ( through the hole ) before withdrawing the shaft ? Then the propeller would be whinched up, out of harm's way. I shudder to think how the crew could have done this in darkness, with ice all around.ReplyDelete
Very thought provoking documentation. Congrats on a job well done!