I’m tremendously interested in the ways technology evolved in the 20th century. There are so many things we use today that simply didn’t exist at the end of the 1800’s. And yet here we are, taking ocean voyages on vessels with gyroscopes to stabilize them, watching planes take off from the deck of carriers, lighting our world with bulbs instead of flames. For me, one of the most fascinating innovations of that time is the use of model basins for the testing of scale-models of ships before the ships were built –- a practice still in widespread use today.
At the start of the twentieth century, the US Navy needed to design ships of metal, with propellers and engines, to replace their fleet of wooden sailing vessels. Until that time the norm had been to build a ship and then see how it performed. This time, the Navy decided to follow the example of the navies of Europe and test scale-models first. But before they could test the models, they needed a place to test them.
They chose David Watson Taylor, a brilliant mathematician who’d graduate with distinction from both the US Naval Academy and the Royal Naval College in England, to oversee the construction of the Experimental Model Basin at the Old Navy Yard in Washington, DC. His task was to construct a basin – trench – to test the models, record his findings, and use those results to suggest modifications to the design of the vessels before any work on them was begun. It wouldn’t be as simple as it sounds.
The first thing Taylor had to do was construct a basin and a building to house that basin on the ground provided by the Navy. They gave him land very close to the Anacostia River, with weak streams running underneath and quicksand at one end. Taylor had his plans. He had his land. And he had no time to waste. He came up with the idea of preparing the ground beneath the basin, then driving pilings into the soil on either side of the space for the walls of the basin and creating a wall around that area. The intent was to keep the water in the soil from exerting pressure on the outside floor and walls of the basin – which would cause it to collapse when not filled. His modifications worked and the walls stood.
He decided to use alum to get the dirt in the water from the Potomac –- used to fill the basin –- to settle before it was in the basin because he needed clear water. He came up with the idea of allowing a stream to run into the basin to keep it filled with a constant amount of water. He designed baffles and wave breakers to settle the motion of the water between tests and designed a massive towing carriage to run along tracks mounted on the upper edges of the basin while towing the models through the water in the basin….
He did all this before he could even get started. When he finally was ready to test the models he found that the paraffin models had lost their shape in the heat of a DC summer. But he couldn’t wait for cooler weather and he had no way to keep the water cooler. He needed something else and here is where his innovation saved the day. Taylor decided to make his models out of pine because it would hold its shape and was in plentiful supply. To make identical models posed a problem. Doing it by hand just didn’t afford the necessary precision. He designed a machine that would turn out identical model forms. While he was at it, he realized he could build the models in a way that would allow different types of hulls and other external parts to be varied by test. Now that he had the identical models, he needed a uniform surface. He hit upon painting each model part with several coats of varnish – ensuring a smooth surface.
Taylor’s tests formed the basis of many of the principles of hull design still in use today. His work on the “wetted surface of ships,” the optimal ratio of width to length of a ship, the type and pitch of propeller, the use of a bulbous bow beneath the waterline… All of these came out of Taylor’s testing. And he was one of the founding members of NACA –- now NASA –- because of his conviction that it would someday be possible to transport planes on ships.
Rear Admiral David Watson Taylor. I’ll write more about his work in the future!
Click on the Fluids tab and search in Fluids in Motion for more about David Taylor.
Originally posted August 20, 2008 on The Witches of Agnesi