The Titanic’s rudder was too small

This has been a popular assertion for the last fifteen years or so, particularly among observers with little or no knowledge of ship design or construction, and is even perpetuated on various Titanic “historical” websites that claim to be authoritative.  One such example, which could serve as a summation of this claim as a whole, states: [The Titanic’s] stern, with its high graceful counter and long thin rudder was, in fact, a copy of an 18th century steel sailing ship, a perfect example of the lack of technical development…. Apparently no account was made for advances in scale and little thought given to how a ship 852 [sic] feet in length, might turn in an emergency….”

As with most aspects of shipbuilding, however, what at first might seem obvious or self-evident is not the case.  Simple size is not the only factor in determining how effective a rudder will be in turning its ship–shape, its position in relation to the screws (propellors), and the ship’s speed are all contributing factors as well.  William H. White, in his Manual of Naval Architecture, published in 1900 and one of the standard marine design handbooks of the day, makes the point quite tellingly that “a broad rudder, with an area 37 per cent. greater than the narrow one, has therefore less turning effect by about 11 per cent.”  This is due to “stalling” of the rudder, where the size of the rudder actually impedes the steady flow of water over its surface, reducing the leverage that the rudder exerts on the hull of the ship.

To understand how and why this is so, it’s important to be aware of how a rudder does its work–how it actually makes a ship turn.  The leverage generated by the rudder through the flow of water created by the movement of the ship is what directs the ship’s stern to the left or right, depending on which way the rudder is turned. As the stern swings out, the ship pivots on a center-point, located more-or-less amidships, and the bow moves equidistantly in the opposite direction of the stern.  The thrust of the propellors pushes the ship ahead, and the process continues until the rudder is centered.

While at first glance it would then seem that the larger the rudder, the more leverage, that isn’t the case: the rudder has to work within that flow of water along the hull; if it interferes with it, the rudder will actually lose effectiveness.   Or, as Parks Stephenson, systems engineer, maritime historian, and retired naval officer, rather succintly puts it, “Where rudders are concerned, bigger is not always better.”

The size of a ship’s rudder then is not a matter of guesswork or “cut-and-try.”  In the case of the Titanic, the aforementioned manual by William H. White, would have served as a authoritative reference and guide for the Harland and Wolff designers and engineers.  Its full title is A Manual of Naval Architecture for Use of Officers of the Royal Navy, Officers of the Mercantile Marine, Yachtsmen, Shipowners and Shipbuilders–the tome runs some 750 pages, and it would have been considered to be something close to the bible of ship design in its day:  for over two decades White had been the lead designer of warships for the Royal Navy, including some of the most successful battleship and cruiser classes of the period.  He possessed not only the theoretical knowledge but also the practical experience to be able to make firm pronouncements regarding the technical aspects of ship design.  In his Manual, White stated that “for steamships…the extreme breadth of the rudder [is often] from one-fortieth to one-sixtieth of the length…in merchant ships much smaller rudders are used, and values as low as one-hundredth have been met with.”  For the Titanic, the maximum width of her rudder was 1/59th of her length, not only within the range stated to be acceptable for warships, but well within the accepted ranges of merchant marine ship design.   So, in answer to the question “Was the Titanic’s rudder too small?” the answer is a resounding “No!”

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