Small Vessel Engineering - 2nd Engineer Auxiliary Equipment 1 Propulsion Past Questions & Answers

We need to keep a close eye on the blade position and manually maintain the position should they wander.

We need to rely on the backup system available, which may include a local hand pump to change pitch manually, a 'fail to full ahead' system where the blades move to the limit of forward travel by spring pressure, or accessing the end of the control rods in the engine room.

The push-pull rod is moved against a large spring in the hub, and relief of pressure against the piston allows the rod to return, so total failure of pressure results in the blades moving to the limit of forward travel by the spring pressure.

The end of the control rods can be accessed via the Oil Distribution Box or gearbox.

The three main options are: 1) A local hand pump to change pitch manually, 2) A 'fail to full ahead' system where the blades move to the limit of forward travel by spring pressure, and 3) Accessing the end of the control rods in the engine room.

The large spring in the hub is used to move the push-pull rod, so that total failure of pressure results in the blades moving to the limit of forward travel.

The blade position needs to be closely monitored, and manually adjusted to maintain the desired position.

Smaller parts of the ship begin to resonate, which means they start vibrating at their natural frequencies, causing the ship to vibrate excessively.

Skew is used to reduce cavitation and noise.

The pitch of a propeller is the distance the ship will move with one rotation of the propeller under ideal conditions.

Slip is the difference between the theoretical distance a propeller should move the ship in one revolution (the pitch) and the actual distance moved. This is because water is a 'yielding' medium, and it flows around the blades, reducing the efficiency of the propeller.

The rake of a propeller blade is the angle at which the blade is angled relative to the propeller shaft. Rake is used to optimize the performance of the propeller by reducing cavitation and improving efficiency.

The pitch of a propeller is the theoretical distance the ship should move in one revolution of the propeller. However, due to the 'yielding' nature of water, the actual distance moved is less than the pitch, as the water flows around the blades, a phenomenon known as 'slip'.

Cavitation is the formation of vapor bubbles in the water due to the low pressure created by the rotating propeller blades. Cavitation can cause damage to the propeller and reduce its efficiency, which is why design features like skew are used to mitigate it.

The 'yielding' nature of water means that it gives way as the propeller blades move through it, rather than providing a firm medium like wood. This results in 'slip', where the actual distance moved by the ship is less than the theoretical distance based on the propeller's pitch.

The rake of a propeller blade is the angle at which the blade is angled relative to the propeller shaft. Rake is used to optimize the performance of the propeller by reducing cavitation and improving efficiency, as it helps to shape the flow of water around the blades.

When smaller parts of the ship begin to resonate, they start vibrating at their natural frequencies, causing the ship to vibrate excessively. This can lead to structural damage and compromise the overall integrity of the ship's components.

The stepped flange design ensures correct alignment with the CPP hub when bolting it to the flange.

The fitted bolts ensure the faces are clamped tightly together, while the dowels ensure a full and correct installation of the CPP hub.

The pilgrim nut is used to press the propeller onto the taper of the shaft using hydraulic pressure, ensuring a correct fit.

The pilgrim nut's nitrile tyre is pressurized, expanding the loading ring to push the propeller onto the taper to a predetermined 'shop-mark' distance. The pressure is then released, and the nut is tightened fully and locked in place.

If the clearance between the propeller tip and the underside of the stern is too tight, it can form pulses that induce vibrations into the hull.

If the propeller speed coupled with the main engine vibrations aligns with the natural vibration nodes (global or local) of the vessel's hull, it can induce or amplify hull vibrations.

Increasing the number of propeller blades results in higher frequency vibrations induced by the propeller.

The key components are: a controllable pitch propeller, a thruster tunnel or aperture in the hull, a drive motor or engine, and a control system to adjust the propeller pitch.

Setting the pitch to zero thrust prevents any accidental thrust being generated when initially starting the propeller rotation, avoiding potential hazards or unintended movement.

With a controllable pitch propeller, the blades can be rotated to a zero pitch position, allowing the propeller to spin freely without generating thrust. This means the drive can potentially keep the propeller rotating continuously.

Underwater obstructions like ropes or debris can become entangled in the rotating propeller blades, potentially damaging the propeller and requiring time-consuming removal efforts while submerged.

The process would involve: 1) Ensuring the propeller pitch is set to zero thrust, 2) Starting the drive motor to begin propeller rotation, 3) Adjusting the propeller pitch to the desired angle to generate thrust in the required direction.

Additional considerations include: ensuring a clear area around the thruster apertures for personnel safety, checking for potential underwater obstructions, and being aware of the thruster's effects on the vessel's maneuverability and positioning.

The controllable pitch allows the propeller blades to be rotated to an optimal angle for generating thrust in the desired direction while minimizing energy losses. This angle can be dynamically adjusted based on operating conditions for improved efficiency.

The key components are an electric motor, a propeller shaft, and a tunnel housing. The electric motor drives the propeller shaft, which turns the propeller inside the tunnel housing to generate thrust for maneuvering the vessel.

If the control system fails, maneuvering can be maintained by using the vessel's auxiliary thrusters, rudders, or other available maneuvering systems until the control system is repaired or the vessel reaches a safe location.

If the hydraulic system fails irreparably and the blades assume zero pitch, the vessel should reduce speed to avoid overspeeding the propeller shaft, and use auxiliary propulsion or maneuvering systems to continue the voyage at a reduced speed until reaching a safe location for repairs.

An electrically driven tunnel thruster requires a substantial electrical supply to power the electric motor, which must have speed and directional control capabilities to adjust the thrust and maneuvering of the vessel. The electrical control system must provide precise control over the motor's speed and direction.

To simplify the sketch, it should show the electric motor, the propeller shaft connected to the motor, and the tunnel housing enclosing the propeller. Since the question specifies a fixed-blade propeller design, the sketch can omit any components related to controllable pitch propellers.

If the hydraulic system fails and the blades assume zero pitch, overspeeding the propeller shaft can lead to excessive vibration, potential damage to the shaft and bearings, and potentially catastrophic failure of the propulsion system.

Electrically driven tunnel thrusters offer improved maneuverability, precise control over thrust and direction, and the ability to generate thrust in multiple directions. They are also more compact and can be positioned strategically on the vessel for enhanced maneuvering capabilities.