Missing Figures
In The fall of 2004 I purchased a boat and outboard. The company that built the boat also had the responsibility of mounting the out board. Unfortunately the company built the transom of the boat to high and this had a major effect on the boats performance. With the prop so close to the water’s surface the out board would ventilate ever time I tried to get the boat up on step. It would also ventilate on tight turns at high speeds. Unless I wanted to ship the boat back down to Seattle for modifications I would have to find a propeller that would operate effectively near the surface. The follow is some of the things I learned while solving this problem.
As the propeller rotates (fig 3-1) it forces water down and back as this is happening water must move into the void created by the spiraling blades. This creates a pressure differential across the blade- Low pressure on the back side and high pressure on the front side. This causes water to be sucked into the propeller and accelerated out the back (fig 3-3) much like a house-hold fan (fig 3-2). This action creates the thrust that drives a boat.
It is common knowledge that water boils at 100deg C (212deg F) at sea-level atmospheric pressures. Water will also boil at much lower temperatures if the pressure is reduced. This is the key to understanding cavitation. As an object move though the water at increasing speeds the fluid on the side and back of the object experiences a decrease in pressure. On a propeller this area of low pressure is on the back side of the leading edge.(see fig 3-1)
Pluse-
If this decrease in pressure is great enough it can cause the sea-water to boil (Vaporize). Once these bubbles of vaporized water travel down current to the front of the propeller they enter the high pressure side of the blade and are condensed back into liquid very rapidly. These small implosions of water vapor can cause cavitation burns on theblade and lower unit of the outboard. (see fig 4-21)
4-21
From a functional stand point these bubbles can compromise the outboards performance. As the water vapor travels from the back to the face of the blades they can decrease the water load on the prop (water contact surface with the propeller blades).
...lt in water. Although water is generally considered to boil at 100°C (212°F), water actually boils when the vapor pressure is the same as the air pressure around the water (Physics, 2006). Because of this the boiling point of water is lower in lower pressure and higher at higher pressure. Did you know that baking cookies above 3500 feet above sea level require special cooking directons (Burt, 2004).
Actually the idea is quite simple really, it consists of a floor above the hull with open drain plugs in the rear of the boat and above the water line. By this simple method as water comes in to the boat it will drain right out of the back. If too much weight is in the boat then water will simply come in through the drain holes. This is no worry to me because I can always just put some plugs in the drain holes when carrying a heavy load. I made the decision to build the aluminum skiff 17ft long and strong enough to hold an outboard motor with a mass of 141kg (approx. mass of 90Hp Mercury).
American author, Stephen Crane often wrote about different predicaments that his fellow men encounters. “The Open Boat” is a fictional account of his experience as a correspondent shipwrecked while on expedition to the Cuban revolutionaries in 1897 (http://www.poetryfoundation.org/bio/stephen-crane) where he spent over 30 hours on a life boat with three other passengers. This realistic story depicts how four men are forced onto a 10 foot dingy after their ship sinks. Crane takes a realist approach when describing the natural elements such as unsettling winds and the raging seas which represent the uncaring and unforgiving nature of life. Clearly, Crane narrates the role as the correspondent, while he provides dialog to provide an understanding on how the other passengers are feeling. “The Open Boat” demonstrates that man cannot survive the natural elements and hardships while isolated in the sea without an understanding of nature.
Personal Watercrafts or "jet skis" are basically Personal Watercraft (PWC) are basically small inboard boats able to travel at high speeds due to large amounts of power and very light weight. Alomst all PWC's are under 600 lbs and most of todays PWC's have at least 90 hp.Not only are PWC's some of the fastest water vehicles they are also some of the most maneuverable water vehicles. This is because PWC's propultion is based on a jet that also is it's turning mechanism. When the driver turns the handlebars the jet (via cables) turns in the direction of the handlebars so the stern is pushed in the opposite direction. This allows the driver to turn at a much tighter angle than traditional boats with keels and rudders.The main drawback to this maneuverability is the fact that if there is no thrust coming from the engine the ability to turn is effictively zero meaning that anytime the driver presses the kill switch (a large red button) they lose all ability to steer. This is extremely dangerous whenever an inexperienced person may drive the PWC back to dock or into shore. PWC's have no brakes and have no ablilty to stop other than turning around. They have an extremely efficient ability to hydroplane (when most of the PWC is above water) and it takes most PWC's a few hundred feet to come to a stop after being at full throttle. This is because 600 lbs + a rider is traveling at a very high speed with only minimal friction to slow them down (since PWC's are made to travel with very little friction).
Aerodynamics is generally summarized in these 2 terms: “Lift against Weight” and “Thrust against Drag”. This basically means the amount of flight power generated must be equal to, or greater than the amount of weight of the airplane, and the amount of pushing generated, must be equal to or greater than the airs resistance. But the overall question, so far, is how is “Lift” and “Thrust” generated? The answer to how “Thrust” is generated is quite simple. Its sort of how a car would move, except in a much different way. Airplanes have 4 engines, which can each exert easily up to 200 PSI of air (pressure per square inch), composed of liquid fuel cylinders, and internal combustion (like a car). It also tops to 250 km per hour on the runway! But how “Lift” is generated is, the true definition of aerodynamics. The first thing you must consider to understand this is that the wing of the plane is specially designed, to force the air above the wing to rush faster, than the air beneath it. This works according to the “Bernoulli’s principle”. The reason air above the wing must be fast...
As surprising as it may seem, one of the most common household items, cardboard, can be used to construct a boat. Building a cardboard boat has become a fun activity that anyone can take part in. Towns and schools hold annual cardboard boat regattas, judging the entrants on speed, design, and creativity. In New Richmond, Ohio there is even a cardboard boat museum! These special boats are more than just a box thrown into water; they are designed using elements of engineering and physics to make them not only water ready, but fast and durable. Building cardboard boats is an exciting way to incorporate topics studied in the classroom into an exciting educational experience.
On a evenly balanced and stable ship, these two forces are equal and cancel out each other, but all of this changes when a boat gets shoved over her side. Instead of being equal, the two forces are offset. The center of gravity stays the same but the center of buoyancy migrates to the submerged side, where more air has been forced below the waterline. With gravity pushing down to the center and buoyancy pushing up from the submerged side, the ship pivots on its center and returns to an even keel. The more the ship heels, the farther apart the two forces act and the more leverage the center of buoyancy has. To simplify, the lateral distance between the two forces is called the righting arm and the torque generate is called the righting momentum. Boats want a big righting momentum so they will right from extreme angles of keel.
Pressure relief valves are used to safely contain pressurized gases and liquids. Throughout the years there has been an increased demand for safety in industrial and other related operating practices. These valves are one of the many devices that have been created in conjunction with standardized design and operating practices, for the provision of this very protection. In the past, vessels that now would obviously require relief valves were heated often resulting in drastic increase in pressure within the vessel. This resulted in an extremely dangerous outcome physically for all the parties involved.
When the sailboat is going sideways and heeling the water creates resistance on the keel to counteract the sideways force of the wind and result in a forward movement (Wolfe). But how can a smaller keel counteract the force on a much larger sail? Well the density of water is 1000 kg/m^3 and the density of air is 1.2 kg/m^3, so water is approximately 833 times denser then air. This means that more force is being exerted per square meter on the keel than the sail, so even though the keel is smaller it is still applying enough sideways motion to counteract almost all of the sideways force in the opposite direction created from the sail. On some larger sailboats there are ballasts, which are heavy weights in the bottom of the keel. Gravity pushes these heavy weights and it tries to go to the lowest point it can which would be when the keel is straight down and the sailboat is straight up. The acceleration of gravity is 9.81 m/s and this multiplied by the mass equals the force, so that means that the greater the mass of the ballast the more force is applied to straightening the heel of the sailboat and counteracting the sideways
against the water and to move the hull higher. The force of the water against
Take your manufacturing process to the next level with STOBER Drives ServoFit motion control applications.
Firstly, the gas turbine engine operation begins with the air intake process. As of all internal combustion engine, oxygen is required to support the combustion of the fuel and the source of oxygen is from the fresh air that is taken in. Initially, the fan is rotated by a driving shaft that is powered by the turbine of the engine. A negative or vacuum pressure at the intake side is then created by the rotating fan. Next, the surrounding air is drawn towards the inlet and causes it to flow into the gas turbine engine inlet (Cengel & Boles, 2011). At the same time, the pressure on the other side of the fan is increased as it is compressed at a lower pressure ratio and causes the air in the outlet side of the fan to move fu...
This along with the lighter construction of a two-stroke makes it the preferred motor used in small vehicles and tools (Two Stroke Engine). A two-stroke engine is operated by first drawing the mixture of fuel and air into the chamber by the vacuum caused by the upward stroke of the piston. During the downward piston stroke, the poppet valve is forced closed due to the increased pressure within the chamber. The mixture is compressed in the chamber throughout the stroke. As the stroke ends, the intake port is exposed allowing the mixture to escape into the main cylinder, expelling the exhaust gasses in the process and some of the fuel mixture as well. Momentum then causes the piston to rise, compressing the mixture as another stroke is beginning. Once the stroke reaches its peak, the spark plug will ignite the mixture causing the fuel to expand driving the piston down thus completing the cycle while additionally initiating a new
To understand how this motor works, we must understand the relationship between electricity, and magnetism or simply put electromagnetism. Direct electric current in a simple description: There are two requirements for current flow. The first is a source of electrical potential energy or EMF (electro motive force,). The second is a conductor that provides a complete loop to carry the current. The reason a conductor will conduct is found on the atomic level. A conductive atom’s valance shell is not completely full electrons will flow from atom to atom because of this. When these electrons move from one atom to another that is electrical current (a brief description that is).
Most people have some sort of familiarity with submarine crafts; most of which are most likely related to the navy. This is a very accurate depiction of submarines, as they are primarily used for this, however, they are used in areas of scientific research as well. The purpose of this web page is to go into the history of the submarine to see how it has developed over time. We will also look at how a submarine works, from a physics standpoint.