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Thursday, February 07, 2013

Review of Ships' Bilge Pumps: A History of Their Development, 1500-1900

Review of Ships' Bilge Pumps: A History of Their Development, 1500-1900:


Texas A&M has a department of nautical archaeology (be still my beating heart - http://nautarch.tamu.edu/,) and they publish a journal Studies in Nautical Archaeology which in turn prints small monographs on assorted areas of interest. This small book is number 2 in that series.

Here's a piece of useful physics: "The proportional rate of water flow varies as the square root of the depth of the hole below the waterline [in a ship:]" so a hole 16 feet below the waterline will admit water 4 times faster than a hole 1 foot below the waterline. And when the water in the hold reaches the waterline, sometimes an equilibrium is reached and the ship can continue to float indefinitely, especially if the water being pumped out (and it becomes easier as the water approaches the waterline) becomes equal in volume to the amount of water entering the ship. That's why every ship had to have a bilge pump of some kind.

There is all sorts of material available about ships' rigging, naval tactics, etc., yet little research into the one item on board that might mean the difference between swimming or staying afloat. Obviously the effectiveness of the pump was crucial and constantly being refined. Leaks were common in wooden ships and the location of a leak could often be learned by placing an object (empty pot, for example) against the hull and listening for the telltale rumbling of a leak and then moving the pot until the sound was loudest. Often leaks could be repaired or slowed (and often had to be) during the voyage. Apparently, the properties of salt beef after residing in a cask for several months made quite a good caulking material (better for that than the sailors' stomachs, as well, I suspect.)

The smell of bilge water could also tell of the ship's soundness. If it really, really, stank, there was probably little leakage. When the water was relatively "clear and sweet" you've got a problem. The pumps often made the difference between life and death.

The earliest bilge pumps were made of straight lengths of trees, usually elm which survives well in a wet environment, which were then bored out using a series of drills and augurs. Leonardo was know to have designed a machines that would bore these holes. The tubes for use in a ship would normally be of one piece and about 25 feet long. There were several techniques used to pull the water up, often requiring six-ten men pulling at the end of the rope. One was a leather device that opened out against the sides of tube, pulling and pushing water up above it, much like an umbrella, and then collapsing toward the center as it was lowered back down to the bottom. As metal use became more common, a lead, hub-like, circle with holes was covered with a piece of leather attached in the center to a pole. The leather wold be forced up on the way down and collapsed back against the lead by the force of the water as it was drawn up out of the bilge.

Bronze and copper and steel soon replaced wood and developments in the steam engine had their effect on improvements in the pump. As the need to make closer and closer tolerances for the piston and cylinder in a steam engine were required, improvements in general pump technology inevitably followed. By 1798, double piston pumps were in use, although there is some evidence that two single piston pumps were preferred because if one broke down the other would remain in operation, whereas the double-piston pump was more complicated and if something broke, pumping stopped.

The Chinese had very clever chain pumps that removed the water far more efficiently, Juan Gonzales de Mendoza wrote in 1585: The pumps which they have in their ships are much differing from ours, and are far better. They make them of many pieces, with a wheel to draw water, which wheel is set on the ships sides within, wherewith they do easily cleanse their ships, for that one man alone going at the wheel doth in a quarter of an hour cleanse a great ship although she leak very much. There is evidence the Romans used chain pumps but their technology had been lost until reintroduced in Italy during the middle ages for use in mines. By 1768, a new chain pump had been introduced on an English naval vessel that was extremely efficient, removing 1 ton of water in 40 seconds using only four men. The only drawback was a tendency of the chain to break and the necessity of replacing the leathers often. The United States was slow to adopt the chain pump until the 1830's. In fact, captured British warships had their chain pumps removed and replaced by the older common pump even though a seaman at a common pump could usually work only for 200 strokes, or about 5 minutes, whereas on a chain pump for thirty minute . By the mid-nineteenth century, industrial production of pumps was common and the classic hand well pump we are all familiar with at parks became common.

The book has lots of wonderful photographs, illustrations, schematics and woodcuts to help visualize the written descriptions.


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