Memorial Day Answer
Stars today for Dan, Lynn, and Frederick. The item was the first submarine the �Turtle� (1776). It was invented by David Bushnell (no known likeness exists).
He thought it looked like two turtle shells clamped together, but others who saw it thought it looked like two clam shells. (We always seem to see pictures of the �fat� view. A top view shows the �clam shell� look.) It was of carved oak (�at least six inches thick�) and tarred liberally. Bushnell was secretive. No known drawings of his invention exist and his early descriptions were written in Latin. Later, Thomas Jefferson received two letters describing the craft. Only a few other descriptions have been located. Owing to modern day computer generation and the laws of physics "Turtle" was estimated to be a fat, flattened artillery shell shaped hollow container about seven feet long, and four feet wide, tapered at the bottom more than the top where there is a brass hatch for the occupant.
It was positively buoyant and when in the water, it projected about 12-16" above the waterline when occupied. It was human powered and the controls were cranks to steer the craft with a rudder and windmill type propellers�not screws as shown in some renderings. The controls, from what information has thus far been discovered were inadequately sized, massively underpowered, and in a cramped, air sealed environment, where the pressurized atmosphere and difference between the inside and exterior temperature and humidity generated from the pilot made it rain, fog, and steadily compress the pilot�s ear canals and sinuses. Judging from 1970�s tests with a replica it could be very uncomfortable.
Maximum speed was about three knots, and in a river or against the tide over that speed it was impossible to recover using the controls as they were described by surviving documents. In 1977 a full sized model (using �� planks as the six inch oak was not available) was made and tested in the Connecticut River. Much of what is known about the shape and control comes from their data. The 1977 replica had to take license with shape because if built by the rounded depicted drawings we remember from our text books, the thing would not float, float too well, not stay upright (the brass hatch was on the top), or be unstable and bob like a fishing lure. The model eventually used more than 2100 pounds of lead as ballast. Bushnell said he used 900 pounds, but his boat was far heavier (estimated 2500 lbs.) with the thick carved oak.
Regardless of any shortcomings the vessel had no tether, and was capable of operating in three dimensions, so as a proof of concept the Turtle boat was a success. As a platform of war it was a failure. Still, unlike the Hunley of the civil war it didn�t kill three crews (27 men) to sink a ship. In the Turtle time submerged was a maximum of 30 minutes. But each minute caused air to be used. Carbon dioxide built up and just when you needed the fresh air the most to pump out the water (about 600 pounds worth) to increase buoyancy to resurface, the air was getting bad. In the replica it took several hundred pumps with each arm to push out the sea water let in through the bottom to allow the vessel to submerge, but with each pump of the arm operated leather bellows operator energy was used, endurance wore down, more air was required by the pilot to do the work, and the pressure inside the vessel built up.
The 1977 replica is in a museum in Connecticut River Museum, Steamboat Dock, Essex, Connecticut. In 2003 a different �Turtle� a little fatter was made by Handshouse Studio and tested for the Discovery Channel and supported by several woodworking and metal working guilds. This time the U.S. Naval Academy did tests on the 2003 craft. It too worked (dived to about 15 feet) but, again, awkwardly. More on any browser.
The original Turtle was lost when its mother ship was sunk with the Turtle on board. Because it failed to sink a ship a new submersible boat was not pursued further by Bushnell.