Category Everyday Science

It is likely that the first boats were made of hollowed-out tree trunks. Perhaps early humans saw fallen hollow logs floating along a river and realized that they could carry goods and people. Tree trunks were hollowed using stone axes and fire. A dugout pine canoe, found in the Netherlands, is thought to be at least 8000 years Old.

The oldest discovered boat in the world is the 3 meter long Pesse canoe constructed around 8,000 BCE; but more elaborate craft existed even earlier. A rock carving in Azerbaijan dating from ~10,000 BCE shows a reed boat manned by about 20 paddlers. Others argue that hide boats (kayaks) were used in Northern Europe as early as 9,500 BCE.

Nothing remains of these early boats – which have long since rotted away; but, knowing what plants and tools were available at the time, anthropologists can guess at the kinds of watercraft they used. The current theory is that bamboo rafts like the one shown below were used. Recently, this hypothesis was tested by building rafts using Stone Age techniques and replicating critical crossings.

It’s easy to characterize the Vikings as bloodthirsty reprobates rampaging across Europe, but the craft and innovation of the shipbuilding that enabled their conquests deserves recognition.

The fact that Leif Erikson led a Viking crew to North America in around 1,000 — 500 years before Christopher Columbus set foot on the New World — makes clear the Vikings’ remarkable maritime prowess and showcases the robustness of their boats.

The design principles that led to the Viking longship can be traced back to the beginning of the Stone Age and the umiak, a large open skin boat used by Yupik and Inuit people as long as 2,500 years ago.

Picture Credit : Google

Sailors cannot change the direction of the wind, but thin they are not powerless to change the direction of their sailing boats. By steering a zigzag course, called tacking, they are able to sail in the direction they require. This can be a time-consuming process. It is important that the navigator keeps an accurate check on the boat’s position, so that it does not travel too far off course while tacking.

If your destination lies upwind, how do you sail there? Unless the wind is blowing from directly astern (over the back of the boat), the sails propel the boat forward because of “lift” created by wind blowing across them, not by wind pushing against them. As you steer more toward the wind direction, you trim the sails in tighter to keep them full, and keep generating lift. But sail too close to the wind and the sail will “luff”— the forward edge will start to flutter in and out and the boat will slow down. Turn more into the wind and soon the whole sail will be flapping like a bed sheet hanging out to dry. But keep turning through the wind and soon the sail will fill on the other side of the boat. This is called “tacking.”

Modern sailboats can sail up to about a 45-degree angle from the wind. For example, if the wind is blowing from the north, a boat can sail from about northeast on port tack (“tack” also describes which side of the boat the wind is blowing from: “port tack” means the wind is coming over the port, or left, side) all the way through east, south and west to northwest on the starboard tack (wind coming over the right side of the boat).

On the new tack, you’ll find you’re sailing in a direction that’s at about right angles to the old tack, with the wind still at about 45 degrees, but now on the other side. Tack again and again and the zigzagging will move the boat upwind, even though the boat can’t sail directly into the wind. Sailors call this “beating,” or “tacking,” to windward, and doing it efficiently takes more skill and practice than anything else in sailing. But learn to do it well and you can sail anywhere.

Picture Credit : Google

Traditionally, the left hand side of a ship, looking forward, is called the port side, while the right hand side is called the starboard side. The term “starboard” comes from “steerboard”. The large oar used to steer early ships was usually on the right. “Port” comes from the fact that ships had to tie up on the left side in port so that their steering oar would not be crushed against the dock.

Since port and starboard never change, they are unambiguous references that are independent of a mariner’s orientation, and, thus, mariners use these nautical terms instead of left and right to avoid confusion. When looking forward, toward the bow of a ship, port and starboard refer to the left and right sides, respectively.

In the early days of boating, before ships had rudders on their centerlines, boats were controlled using a steering oar. Most sailors were right handed, so the steering oar was placed over or through the right side of the stern. Sailors began calling the right side the steering side, which soon became “starboard” by combining two Old English words: stéor (meaning “steer”) and bord (meaning “the side of a boat”).

As the size of boats grew, so did the steering oar, making it much easier to tie a boat up to a dock on the side opposite the oar. This side became known as larboard, or “the loading side.” Over time, larboard—too easily confused with starboard—was replaced with port. After all, this was the side that faced the port, allowing supplies to be ported aboard by porters.

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A periscope is a metal tube that can be extended above the submarine while it is underwater. The tube contains lenses and mirrors, which enable an image of the scene above the surface to be seen below in the submarine. The periscope can swivel, so that a 360° view is obtained. The operator turns the periscope by means of the handles on the side. These fold up when it is not in use, as space is always at a premium in a submarine.

Periscope, optical instrument used in land and sea warfare, submarine navigation, and elsewhere to enable an observer to see his surroundings while remaining under cover, behind armour, or submerged.

A periscope includes two mirrors or reflecting prisms to change the direction of the light coming from the scene observed: the first deflects it down through a vertical tube; the second diverts it horizontally so that the scene can be viewed conveniently. Frequently there is a telescopic optical system that provides magnification, gives as wide an arc of vision as possible, and includes a crossline or reticle pattern to establish the line of sight to the object under observation. There may also be devices for estimating the range and course of the target in military applications and for photographing through the periscope.

The simplest type of periscope consists of a tube at the ends of which are two mirrors, parallel to each other but at 45° to the axis of the tube. This device produces no magnification and does not give a crossline image. The arc of vision is limited by the simple geometry of the tube: the longer or narrower the tube, the smaller the field of view. Periscopes of this type were widely used in World War II in tank and other armoured vehicles as observation devices for the driver, gunner, and commander. When fitted with a small, auxiliary gunsight telescope, the tank periscope can also be used in pointing and firing the guns. By employing tubes of rectangular cross section, wide, horizontal fields of view can be obtained.

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Submarines, unlike most ships, are not always required to float! In order to make a submarine sink beneath the surface, its density must be increased to be greater than that of the water. This is done by taking in water, which fills ballast tanks within the outer hull of the submarine. The amount of water entering can be controlled, so that the vessel sinks slowly. To bring a submarine back to the surface, pumps force the water out of ballast tanks. The submarine’s density becomes less than that of the water it is displacing, so it rises.

To control its buoyancy, the submarine has ballast tanks and auxiliary, or trim tanks, that can be alternately filled with water or air. When the submarine is on the surface, the ballast tanks are filled with air and the submarine’s overall density is less than that of the surrounding water. As the submarine dives, the ballast tanks are flooded with water and the air in the ballast tanks is vented from the submarine until its overall density is greater than the surrounding water and the submarine begins to sink (negative buoyancy). A supply of compressed air is maintained aboard the submarine in air flasks for life support and for use with the ballast tanks. In addition, the submarine has movable sets of short “wings” called hydroplanes on the stern (back) that help to control the angle of the dive. The hydroplanes are angled so that water moves over the stern, which forces the stern upward; therefore, the submarine is angled downward.

To keep the submarine level at any set depth, the submarine maintains a balance of air and water in the trim tanks so that its overall density is equal to the surrounding water (neutral buoyancy). When the submarine reaches its cruising depth, the hydroplanes are leveled so that the submarine travels level through the water. Water is also forced between the bow and stern trim tanks to keep the sub level. The submarine can steer in the water by using the tail rudder to turn starboard (right) or port (left) and the hydroplanes to control the fore-aft angle of the submarine. In addition, some submarines are equipped with a retractable secondary propulsion motor that can swivel 360 degrees.

When the submarine surfaces, compressed air flows from the air flasks into the ballast tanks and the water is forced out of the submarine until its overall density is less than the surrounding water (positive buoyancy) and the submarine rises. The hydroplanes are angled so that water moves up over the stern, which forces the stern downward; therefore, the submarine is angled upward. In an emergency, the ballast tanks can be filled quickly with high-pressure air to take the submarine to the surface very rapidly.

Picture Credit : Google