What is the Advantage and Disadvantage of Underwater thruster manufacturer

One critical aspect of ROV design is the choice between hydraulic and electric thrusters, each with its own set of advantages and disadvantages. In this blog, we’ll explore the differences between these two propulsion systems and discuss the pros and cons of each.

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Hydraulic thrusters are a popular choice for many ROV applications, and for good reason. They operate by using hydraulic fluid to convert mechanical power into thrust.

Electric thrusters are another popular option for ROVs, operating by converting electrical power into mechanical thrust through propellers.

The choice between hydraulic and electric thrusters for ROVs ultimately depends on the specific mission requirements and environmental factors. For precise tasks, missions with limited space, and work at depth, hydraulic thrusters are often the preferred choice. This propulsion systems is more powerful, more stable, and easier to control. In contrast, electric thrusters are more suitable for missions that prioritize simplicity and quiet operation without the need for stability and top notch maneuverability. Think about mapping and exploration missions.

Pros of Electric Thrusters

1. Simplicity. Electric thrusters are simpler in design compared to hydraulic systems, requiring fewer components and less maintenance.
2. Clean Operation. Electric thrusters do not involve the use of hydraulic fluid, reducing the risk of environmental contamination. This makes them a more eco-friendly choice for certain missions.
3. Low Noise. Electric thrusters produce less noise compared to their hydraulic counterparts. Noise reduction is advantageous when working in sensitive acoustic environments or with marine life.
4. Scalability. Electric propulsion systems can be easily scaled up or down to meet specific mission requirements, making them versatile for a variety of ROV sizes and applications. It should be noted that some hydraulic systems can do the same.

Cons of Electric Thrusters

1. Lower Power Output. Electric thrusters typically offer lower power and thrust compared to hydraulic systems. Thus, limiting their suitability for heavy-duty tasks or working in strong currents.
2. Reduced Efficiency at Depth. As water depth increases, electric thrusters are likely to experience reduced efficiency. This is due to the increased hydrostatic pressure, which can limit their depth capabilities.
3. Limited Control. Electric thrusters may provide less precise control over thrust and maneuverability, which can be a disadvantage for certain mission types.

Pros of Hydraulic Thrusters

1. High Power and Efficiency. Hydraulic systems can deliver high power levels, making them ideal for heavy-duty tasks such as deep-sea exploration, construction, and intervention. They are highly efficient in transferring power from the source to the thrusters, resulting in excellent thrust output.
2. Precise Control. Hydraulics offer precise control over thrust and rotational speed, making it easier to perform delicate and intricate maneuvers in challenging underwater environments.
3. Compact Design. Hydraulic components are known for their compact design, allowing for the creation of relatively smaller and more maneuverable ROVs.
4. Reliability. Hydraulic systems are durable and reliable, making them a preferred choice for long-duration missions in demanding conditions.

Cons of Hydraulic Thrusters

1. Complexity. Hydraulic systems tend to be more complex and require additional components such as pumps, reservoirs, and hoses, which can increase the overall weight and maintenance requirements. This does depend on the quality and skill of the ROV manufacturer.
2. Fluid Leakage. Hydraulic systems are susceptible to fluid leakage, which can be a significant concern, especially in environmentally sensitive areas.

SEAMOR Marine Thrusters

We stay true to our reputation and provide you with high-quality hydraulic thrusters. Much of the differences between electric and hydraulic ROV thrusters lies in the hands of the manufacturers and mission type. Each of our thrusters can be replaced separately and are easy to maintain. They just need a good rinse after a day at work. Our modular build allows for very deliberate placement of the thrusters which maximises their proficiency and increases ROV stability and maneuverability to the max. We bet you can’t find a more stable system out there!

An underwater thruster is a configuration of marine propellers and hydraulic or electric motor built into or mounted to an underwater robot as a propulsion device. These give the robot movement and maneuverability against sea water resistance. The main difference between underwater thrusters and marine thrusters is the ability to work under heavy water pressure, sometime up to full ocean depth.

Types of underwater thrusters

There are three general types of thrust devices: the lateral thruster or tunnel thruster, which consists of a propeller installed in a athwartship tunnel; a jet thruster which consists of a pump taking suction from the keel and discharge to either side; and azimuthal thruster, which can be rotated through 360°

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Underwater thrusters can be further divided in two main groups, hydraulic thrusters and electric thrusters. Below are some pros and cons of each type:

• High Power and Efficient
• Precise Control
• Reliability

• Complex
• Fluid Leakage
• Heavy
• Expensive

• Simple
• Clean Operation
• Low Noise
• Versatility
• Low Cost options available[1]

• Lower Power Output
• Reduced Efficiency at Depth
• Limited Control

[2]

Hydraulic Thrusters

Hydraulic thrusters are mainly used on larger work class ROVs, mainly because they take up a lot of space and weight due to the extra components such as valves and pipes.[3] Hydraulic thruster technology is older than the electrical one, they are more rugged and their weight-to-thrust ratio is higher than electric thrusters, but maintenance and piping issues cause some dissatisfaction with users.[citation needed] Weight-to-thrust ratios are higher for hydraulic thrusters than for electric thrusters, but after taking into account the required hydraulic components including valves, hydraulic power units, pipes joints, etc. hydraulic thruster systems come out heavier than electric thrusters.[citation needed]

Electric Thrusters

Electric thrusters are mainly used on battery operated underwater robots such as AUVs, submarines, and electric ROVs. Electric thrusters usually use brushless DC or permanent magnet synchronous motors (PMSM). These motors may be sealed within air- or oil-filled cavities, or use a flooded design that allows water to come into contact with the motor, providing extra cooling and lubrication. [4][5]

Components

The main components of an electric thruster are:

1. Electric motor: The electric motor is the main component of electric thrusters and drives the propeller. Modern underwater thrusters usually use brush-less permanent magnet synchronous motors (PMSMs).[citation needed] In some low-quality thrusters brushless D.C. motors are used. The gain is lower price and the penalty is lower efficiency.[citation needed] In most modern designs, frameless PMSM motors (mainly produced by Kollmorgen)[citation needed] are used to reduce the weight and increase the thermal efficiency. This improves the power-to-weight ratio, but the penalty is higher assembly cost.[citation needed] Danish based Copenhagen Subsea produces electrical ring thrusters, where the power is applied on the perimeter, and the motor components are integrated with a duct.[6]
2. Gearbox: to match propeller torque with motor torque some manufacturers use a gearbox. Most of the time, to reduce the weight and volume of the thruster, the gears are assembled directly inside the thruster shell, which is used as the gearbox housing.[citation needed] In this way the weight is reduced, but repairs become difficult as the spare parts can not be found on the normal market.[citation needed]
3. Direct drive: In some modern designs which use PMSM motors, the ratio of motor torque to its diameter is so high that the motor can rotate the propeller without a gearbox. In direct drive underwater thrusters, the motors are heavier than those used in geared thrusters, but lack of a gearbox compensates for this. Direct drive thrusters have higher reliability, lower noise, and higher efficiency, but the prices are higher than geared thrusters.[citation needed]
4. Motor driver and electronics: Brushless motors need some electronics to be commutated[clarification needed] and control their speed. In early versions the drivers were unreliable and this led to user dissatisfaction when compared with highly reliable hydraulic thrusters. More recently developments in power electronic technology have made the motor driver more efficient and reliable, cheap and small, to be fitted directly to the end of the motor. In modern designs the motor controllers are able not only to control the propeller RPM, but also to control the thrust force in applications that need close control on their positioning.[citation needed]
5. Shafting and sealing: Keeping the propeller in the right place and making it reliable in case of impact with external items such as fishes or fishing nets is one of the main concerns in all kinds of thrusters. Many failures have been reported due to this problem.[citation needed] Some manufacturers try to solve it by using magnetic couplings and totally avoiding rotary sealing. This improves reliability of the sealing and shafting, but they lose in efficiency due to limited torque transfer capability of the magnetic coupling and they solve this problem by using a high-speed, low-torque propeller.[citation needed] In most models the efficiency is as low as 25% which is very low for underwater thrusters.[citation needed] Magnetic bearings[clarification needed] require the propeller to be rotated on the outer shell surfaces using a layer of water as a lubricant, which may reduce the bearing life considerably in contaminated water. Some other manufacturers use tapered bearings and a multiple sealing system for redundancy. In this design if the main seal (usually a ceramic seal[citation needed]) fails, the others seals keep the motor safe and the thruster can continue operation.[citation needed]
6. Propeller: The propeller is the component which converts rotation to thrust. Selection of the right propeller has a considerable influence on the performance a thruster. Each application's hydrodynamic load line needs a matched propeller for maximum efficiency, but there is lack of standard off-the-shelf propeller variation on the market and therefore it is impossible to order the thruster with the best efficiency propeller.[citation needed] Some companies will design and develop custom propellers, but their prices are really high.[citation needed] Other companies try to offer many propellers as options and let the user select the best one using performance charts of their thrusters.
7. Nozzle: Nozzles are used with heavy load, low-speed thrusters. Most ROVs have this type of hydrodynamic loads. In high-speed, light-load robots, such as AUVs, UUVs and submarines, usually the thrusters do not have a nozzle.
8. Propeller guards: Propellers may be damaged by impact from fish or other objects, but may vibrate if the flow to the blades is not uniform. The propeller guard design can affect the flow to the propeller and consequently the performance. Some manufacturers leave the design of the propeller guard to the user, but a more efficient solution is to integrate the function with the nozzle support struts.[citation needed]
9. Shell: Thruster shells usually must be resistant to seawater corrosion. There are two common version of shells; hard anodized aluminium and stainless steel grade 316.[citation needed] Steel is heavier, more expensive and more resilient. Aluminium is lighter and cheaper.
10. Electrical connector: Electrical connectors are important component of underwater thrusters. There is a wide range of reliable components available from third party suppliers.[7]

Performance

Many parameters affect underwater thrusters considerably. Under the sea, energy become more valuable as it is difficult to transfer it (ROVs) or to store it (AUV, UUV, Submarine), Then its very important to have the maximum efficiency. Motor driver, electric motor, shafting, sealing, propeller, nozzle and thruster outer geometry and surface all affect the efficiency.

Contact us to discuss your requirements of Underwater thruster manufacturer. Our experienced sales team can help you identify the options that best suit your needs.

1. Matching the propeller load with motor torque: One of the more difficult design problem of underwater thrusters is to match the propeller load line with the motor power line. If it does not happen the overall efficiency of the thruster will fall well below maximum or only a small percentage of motor power will be used.[citation needed]
2. Using the right propeller: Propeller diameter, pitch ratio and type[clarification needed] are very important to have the maximum performance. Lots of investigation and engineering must be done before final order of thruster to have the right choice.
3. Using low Total Harmonic Distortion (THD) motor and driver: PMSM motors have some efficiency problems with THD. Low-THD motors and drivers are available on the market (Kolmorgen)but their prices are considerably higher than lower efficiency motors. Only high-tech Thrusters on the market using this type of motor and driver (Lian Innovative[usurped]). [citation needed]
4. Streamlined Thruster Shell: Manufacturing of streamlined body and handle have a considerable effects on the efficiency, and manufacturing of the curves in this type of geometry is expensive.[citation needed]

See also

• Rim-driven thruster

References