CLASSS EXPANSION JOINTS
Engineering strength is a vital factor in ship construction to enable a vessel to live a long, safe and productive life. Any structure building, ship, or car chassis needs to be strong and it is equally true for large seagoing ocean liners. As liners progressed from the Mauretanias overall length of 790 feet, by the time the Olympic was launched she was the longest liner in the world with an overall length of 882 feet 9 inches, and the Hamburg-Amerika liner Bismarck launched in 1914 was 956 feet long. The bashing that the North Atlantic regularly gave to the express liners tested their strength. Hogging (whereby a liners bow and stern were lower than normal) occurred when only the midship portion of the hull was supported by the sea, leaving the bow and stern unsupported in a storm. This increased the stresses inflicted, while the flexing of the hull was a natural and inevitable occurrence at sea. Atlantic liners had to endure the most horrific storms year after year, and there are many examples of this. Olympic was to encounter many storms during her career, perhaps the worst of them in December 1921 when she was struck by many heavy waves including one that was estimated at more than seventy feet high. It flooded some of the ships first class accommodation and even damaged fittings as high as the boat deck, putting the Marconi wireless installation out of action and smashing ports in the first class reception room. In one first class cabin, the bed had actually been overturned and landed in the middle of the room! On February 27th 1925 Olympic was steaming through moderate seas at 3 p.m., when an immense wave, seventy feet high, suddenly materialised engulfing the ships bridge, crushing ventilators, breaking windows and twisting the metal compass. The ships engines had to be slowed, and it was considered remarkable that none of the ships eleven hundred passengers were injured. Olympic returned to port having taken more than six days to complete the crossing, but these are merely two instances of storm damage. (3)
Since the Olympic class liners marked an advance of almost one hundred feet in length on the Mauretania, at the time of their design and construction Harland & Wolff acted to try and ensure that they had the necessary strength. These efforts were important both in terms of each liners lower hull, but also their superstructure which this article concentrates on.
In 1911 The Shipbuilder reported that on the Olympic: Above the bridge deck, the deckhouse sides and deck plating are of lighter scantling and have two expansion joints, one forward and one aft, to prevent heavy stresses coming upon the thin plating in a seaway. The main scantlings have been determined by Messrs. Harland & Wolffs long experience with large vessels. Material is massed at the upper flange of the equivalent girder by making the bridge and shelter deck plating and sheer strakes of great thickness and fitting doubling at these points, while the lower flange is strengthened by doubling the bilge plating.(1) Broadly speaking, the expansion joints were each a cut in the superstructure which allowed it to flex, and the leather covering of Olympics forward expansion joint can be seen in on-deck photographs. By including expansion joints in the Olympics design, Harland & Wolff were able to use thinner plating in the superstructure itself. As The Shipbuilder reported, the bridge and shelter deck plating and sheer strakes were of much heavier construction, with the plating doubled. When the luxury liners came into being, the naval architect was faced with the prospect of having to accommodate lavish, wide-open spaces for first classs public rooms, and a strong, structurally sound ship. Onboard Olympic, B-deck accommodated expansive promenade areas, along with the two grand staircase landings, and the á la carte restaurant; while A-deck included the first class reading and writing room, the first class lounge, smoke room and veranda cafes aft. However, while Olympics B-deck promenade areas were generally glass-enclosed, the A-deck promenade was entirely open to the elements (unlike on her sisters Titanic and Britannic). Had the shipbuilders been forced to use much heavier construction in the superstructure, the existence of these spacious features would have been called into question. Olympics widely-admired, open deck spaces would never have come into being.
Considering the changes to the Britannics expansion joints, and experiences on both the Aquitania and Olympic, the issue of assessing their effectiveness at relieving the build up of excessive stress comes to light. And here we need to examine the Olympic and similar ships as well as the Britannics post-Titanic redesign. In March 1912 the Olympic was dry-docked to have a new propeller blade fitted, and the liners hull was examined. Some signs of undue stress were found in the thin deckhouse plating on the bridge deck, in that there were a number of small fractures situated at the edges of the windows. It was reported that: The signs of stress are confined entirely to what is shown here, neither the promenade deck [A] or bridge deck [B] plating nor the bulwark plating at the side showing any signs. It will be observed that these fractures have occurred at the portion of the [deck] houses between the expansion openings [joints] and near to the openings. One very short fracture only was found in the [deck] houses on the promenade deck. It should be emphasized that these fractures, at the edges or corners of the windows, would have been little more than a cosmetic concern, and would probably not be visible unless closely inspected, but they did signify that the issue of expansion joints needed to be examined on large liners. The Olympics superstructure itself was situated above the strength deck, which was B-deck in her case, and marked the top of the structural hull girder. (It is interesting to note that, for this reason, the use of portholes on the Olympic and her sisters was confined to below B-deck: only on B-deck and above were large rectangular windows installed.)
Aquitania was a little longer than the Olympic, and according to The Shipbuilder: The boat and A decks are of lighter scantling, three expansion joints being provided to relieve the superstructure from longitudinal stresses.(2) Yet the Cunard liner brings about the question as to whether three expansion joints would have been preferable to two expansion joints in the long run, and it is not as clear-cut as might be expected. On January 13th 1931 the Board of Trades Senior Ship Surveyor F. W. Daniel wrote: Cases bearing on the same point [i.e. excessive fatigue] are the Aquitania and Olympic, both recently reported. In my opinion, the number of expansion joints could at least be doubled with advantage, so as to allow the stresses being more evenly distributed over the uppermost strength deck. In Olympics case, doubling the number of expansion joints would have brought her total to four expansion joints, although in the Aquitanias case six expansion joints would have marked a doubling of the original designs number. It seems probable that Daniel was referring to four expansion joints being an advantage, since six does seem a high number.
Britannics design underwent some well-known changes after the Titanics loss, and Harland & Wolff envisaged three expansion joints amidships, with a fourth expansion joint added near the after mast due to the structural changes at the stern which included the enclosure of the after well deck. It would have been interesting to have observed her in service, had she not been lost within a year of her maiden voyage, yet the structural changes to the new ship and the addition of the new girder-type davits left the shipbuilders with little choice. Britannic was certainly an improvement upon her sisters arrangement of expansion joints, and Aquitanias for that matter.
The numerous design considerations that need to be borne in mind highlight the Herculaneun task facing Harland & Wolff when the Olympic class liners were designed, and then the Olympic and Titanic built alongside each other. Unlike the third sister, Britannic, Titanic had been launched successfully two weeks prior to Olympics maiden voyage. There would have been precious little time to correct any major problems, and it is a testament to the shipbuilders that none became evident. It is worthwhile remembering these points when assessing the overall quality of their design, although it is unfortunate that only one vessel survived for a significant time in service. Olympic enjoyed a long and glorious career.
My thanks to Scott Andrews for his kind assistance. Naturally any errors in this brief article are entirely my responsibility. (Please note that this article was revised in December 2005 to correct some misleading comments that were contained in the original. I am grateful that these were pointed out.)
(1) Maxtone-Graham, John. (Ed.) Olympic
& Titanic: Ocean Liners of the Past. New York: Amereon House; 1995.