Kipling’s MacAndrew’s Hymn is one of my favourite poems, probably because I used to be a marine engineer. This is an extract:
Fra skylight-lift to furnace-bars, backed, bolted, braced an’ stayed,
An’ singin’ like the Mornin’ Stars for joy that they are made;
While, out o’ touch o’ vanity, the sweatin’ thrust-block says:
“Not unto us the praise, or man – not unto us the praise!”
“…backed, bolted, braced and stayed” is a wonderful summation of good engineering, and anybody who has been in a ship’s engine room, especially one with a slow speed direct drive engine running at full power, will identify with the description of the machinery singing for joy.
Singing main engines or not, the poem is out of date in one respect, when it refers to the “sweatin’ thrust-block”. Thrust blocks have not sweated for more than a hundred years, and this illustrates how seemingly mundane inventions, taken completely for granted, have changed the world.
Every ship in the world has a “thrust block”, a bearing which transfers the thrust of the propeller to the ship’s hull. Nowadays the thrust block is completely reliable, and unremarkable, but this was not so when Kipling wrote the poem.
In the late nineteenth century, steam engines became enormously powerful, driving heavy, ships quickly across oceans. For example, the Deutschland, which in 1900 crossed the Atlantic at an average speed of 23 knots, weighed 22,000 tons, and each of her two engines produced 18,000 indicated horsepower (ihp). Assuming a mechanical efficiency of say, 75%, each engine developed about 14,000 brake horsepower (bhp), and according to my calculations, about 80 tons of thrust. Even a small inefficiency in the thrust block would lead to the generation of serious amounts of heat, wasting fuel, requiring copious quantities of cooling water, and the bearing could seize with disastrous consequences.
No designs were successful until the invention of the hydrodynamic thrust bearing. I have always thought of it as the Michell bearing, but it is more properly the Michell-Kingsbury bearing as it was independently invented by the highly mathematical George Michell, and Albert Kingsbury, who was a skilled machinist as well as an academic. Hydrodynamic thrust bearings rely on a lubricated disc on the rotating shaft, and angled pads on the bearing frame. As the shaft rotates, a wedge of oil builds up between the pads and the disc, so that there is no metallic contact. Michell’s design used pads cleverly hinged near their theoretical centre of pressure, and Kingsbury’s fixed pads.
Such bearings last the life of the ship, and are almost maintenance free. Although their function is obscure and unglamourous, they are the product of remarkable ingenuity, and the modern world, with tens of thousands of ships plying the its oceans depends upon them.