10

In the video you've linked to, the spheres are seen on both the leading and trailing edges of the propeller: I expect they are intentional - there are a number of ways to attach a propeller without having to disturb that surface, or using flush caps. Cavitation is caused by a drop in pressure. This would be seen on the trailing edges of the propeller, and ...


10

From USCG Surge Protective Devices Onboard Vessels A marine casualty investigation of two separate stateroom fires onboard a U.S. Flag Container ship revealed that the sources of the fires were attributed to the use of SPDs plugged into a lighting circuit. It was discovered that a ground had developed on another circuit that was connected to the same ...


5

No, it would just create a torque couple and rotate the boat anticlockwise. Let's say the small propeller has an output volume, q grams/s, and the distance between inlet pipe and outlet is 5cm. The thrust and suction of each end of pipe. $$ F = ρ q (v2 - v1) $$ say density of water is =1, and V1 is initially zero, for simplicity, even though it wouldn't ...


4

the former soviet union had plentiful stores of titanium on hand, so its expense was not an issue. Being nonmagnetic, a titanium hull would be more difficult to detect with magnetometers. Note also that in a properly-designed submarine pressure hull, the limiter is not tensile strength but compressive yield strength and elastic modulus, since the hull ...


4

Your intuition is correct, those are high. However, you would need to be moving very slowly for wave-making resistance to be negligible. And since it is typically higher than skin-friction I don't think that you can realistically expect to have a significant skin friction and a negligible wave-making resistance. Perhaps a better simplified approach would be ...


4

I'm not sure where did you brought the 'deep water relationship' in here. If you're dealing with usual water wave (gravity, surface, linear, and close to sinusoidal wave form), then the relationship you'd need to use will be dispersion relationship. $\omega^2 = gk\tanh(kh)$ As you're assuming deep water, it becomes: $\omega^2 = gk$ Which leads to almost ...


4

We really need more info on the batteries and type of connection. Will the connection be permanent? In that case soldering or welding are the best choices. If you're connecting to wire, you'll need good strain relief. Any repetitive motion at the solder joint / weld will cause failure eventually. In a vehicle the battery may have a tendency to jostle around....


3

The news item said it grounded, pretty typical,along with "hit rocks". There is so much mass in a ship that good steel with a 4:1 design safety factor can't resist fracture in a "crash". The brittle fracture of low toughness steel in WW 2 Liberty ships is not a factor . Said with crossed fingers as just when you make something fool proof, ...


3

As Dave Tweed mentioned, this is a simple example of a diverter valve. It allows flow to be directed to one or the other output. Valve manufacturer site


3

Whether these are sensible Froude numbers or not depends on the length of the vessel in question. For a 100 m ship these are probably high but for a 5 m dinghy these would be quite low numbers. Speed-to-length ratio is the critical factor that determines the importance of skin and wave friction. Skin friction scales with $V^2$, whereas wave drag increases ...


2

Submarine propulsor designers are least concerned about hub vortex cavitation as they are primarily concerned about cavitation inception, or the onset of cavitation, which first occurs in the tip vortex regions, where the velocities are highest. Once cavitation occurs you are no longer operating in stealth mode. However, the hub vortex does waste a ...


2

When fluid flow increases in velocity (because of smaller area of blade root) the pressure decreases and can be low enough to produce cavitation. The spheres produce turbulence changing the flow characteristics, keeping the pressure up. Hub tip pressure drops as flow fills in after the hub and causes cavitation. The flat hub blades disrupt the flow and ...


2

"Hull speed" is actually the ratio of speed to the square root of length. To make things even more confusing, length is in feet, and speed is in knots. That's how the constant 1.34 arises. (ProTip: Let's never speak of it again!) Wave resistance ($R_w$) begins its rapid rise at a Froude number (Fr) of about 0.35. Below that Fr, $R_w$ is usually small ...


2

There is no hard limit on the size of an airfoil/hydrofoil. A ships hull is a hydrofoil. This is how a sailboat sails into the wind for example. A keel is a large hydrofoil used in addition to the boats hull for directional stability or to counteract the force of the sails on a sailboat. Hydrodynamic lifting of vessels for higher speed and higher efficiency ...


2

You intend to submerge a rectangular concrete section in a fairly corrosive environment (ocean water). The section is 11.5" wide and 18" deep. During the 20 year life span of the boat, you anticipate 6 heavy impact events. The concrete keel is intended to act as a beam which is to spread the impact load evenly onto the laminated wood hull to such an extent ...


2

People, people people (by which I mean the unreferenced other answers at this time) ! look it up! Here is info from a Chinese research paper: . Compared with the cross rudder, X-form rudder has the following advantages: Firstly, X-form rudder has the higher rudder efficiency and its manipulate surface area is smaller about 10% than cross rudder, ...


2

×-form surfaces result in a shallower draft. ×-form surfaces are more convenient for landing on the floor. With +-form the bottom fin which stick down below the bottom of the vehicle. From what I've noticed, the littoral submarines have ×-form surfaces, because they are intended for shallow waters.


2

Consider how much energy is needed to heat the fuel that is injected each time compared to the energy that can be recovered from the turbo-charger for example. One thing to note is that many of the diesel pumps (style DPA / inline high pressure) will compensate for changes in the density of the fuel according to the temperature, the modern common rail ...


2

They are HF radio masts that are hinged down for flying operations. My initial thoughts they were radio direction finders or airframe recovery booms, but my research does not support it. In port they are up. With planes in the air, they are down. Four port, four starboard. Two forward, six stern. They are connected by cables. From the-blueprints.com. ...


1

The gravitational force and the buoyancy force create what is known as a moment couple (or sometimes just couple). Essentially they are two equal (because buoyancy and gravity should be equal in a boat), parallel and opposite facing forces, when have a zero translational effect and produce only rotation. See the following example For the above example it ...


1

MV Wakashio ran aground on a coral reef off Mauritius on July 25. MV Wakashio is a 300m Bulk Ore Carrier. It was empty at the time (no cargo). From BBC: Mauritius declares emergency as stranded ship leaks oil: You can clearly see the reef and direction of waves hitting reef. No oil, when this picture was taken. From IPR Mauritius: oil spill from damaged ...


1

There is no one way to do things. Ship design is continually evolving. In general, cargo ships are low and slow, as in powered by large 2-stroke diesel engines with big propellors and slow speeds. Higher speed vessels use smaller 4-stroke engines with smaller propellors and higher speeds. Traditionally, propulsion has been diesel, but as ship sizes get ...


1

This is the end part of the ship during the construction and is not finished yet. This part when finished will be called Stern. The stern houses the rudder and the propellers and follows the keel. It is designed to have a streamlined narrow shape under the water to help reduce the drag of the ship and vibration due to the rotation of the propellers and ...


1

The water starts out stationary. It ends up being jetted out the stern. Yep, that makes thrust. There will be some pressure interaction over the entire hull of the ship. That is geometry dependent. It can be engineered to minimize the parasitic drag from collecting the inlet from the stern. This is basically a thrust reverser in reverse. Amrican Airlines ...


1

It was more a political decision than engineering. The problems with fabricating thick titanium plate are enormous = expensive, and the Russian engineers did a remarkable job. There is much information on the web, but I could not find information on the particular alloy , thickness, strength, toughness, etc. An interesting summary is "Unravelling a Cold War ...


1

I found some possibly applicable explanations here. The figure referred to in the quote below is The attached plot [Hofman 2000] illustrates the basic principles of added drag due to shallow water. A non-dimensional depth-based speed parameter is on the X axis (usually noted as FNH, but shown here as FL), and a ratio of drag in shallow water to ...


1

Everything that gets the mixture in the cylinder hotter makes for a more efficient combustion. That is because the power of the engine depends purely on the pressure exerted on the piston, and the effective pressure is caused by temperature rise, and nothing else. So yes, injecting hot diesel would make for a more efficient combustion, in theory. But it ...


1

The issue isn't necessarily "switching" between reception and transmission, but making sure the receiver doesn't get damaged by the high voltage put onto the antenna by the transmitter. Since the higher level system knows when it's transmitting and when its receiving, it simply ignores the receiver during transmission. Consider the problem of a receiver. ...


1

From this wikipedia article A duplexer is an electronic device that allows bi-directional (duplex) communication over a single path. In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer. Duplexers can be based on frequency (...


1

You are correct that the Froude number (Fr) is very important for wave resistance. The answer given by nivag regarding the speed-length ratio (also known as "hull speed") is not correct. That limit is often quoted, but it is a myth that it is somehow impossible for displacement hulls to surpass it. Ships can travel faster than that ratio implies, but for ...


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