# How to design underwater thruster propeller?

Posted by **Fengyukun** on

**Ⅰ. The design of underwater thruster propeller has the following aspects to consider**

1、Thrust demand: it is necessary to determine the propeller diameter, torsion, number of blades and other parameters by calculating the thrust required by the thruster.

2, hydrodynamic performance: need to consider the propeller blade shape, cross-sectional shape, pitch and other parameters to achieve the best hydrodynamic performance.

3, noise and vibration: the need to optimize the structure of the propeller to reduce noise and vibration, improve the reliability and service life of the propeller.

4、Materials and manufacturing: Suitable materials and manufacturing processes need to be selected to ensure the strength, stiffness and corrosion resistance of the propeller.

**Ⅱ, the design of underwater thruster propeller requires consideration of several factors, which will be explained in more detail below and given the corresponding formula**

1、Thrust requirement

Thrust requirement is the most basic requirement for propeller design. The magnitude of thrust demand is related to the mass and speed of the ship and is usually calculated by the following equation:

F = 0.5 * ρ * V^2 * S * C

Where F is the required thrust, ρ is the density of water, V is the speed of the ship, S is the cross-sectional area of the ship, and C is the drag coefficient.

2、Hydrodynamic performance

Hydrodynamic performance is the key to propeller design, including blade shape, cross-sectional shape, pitch and other parameters. The selection of these parameters needs to be determined according to the specific use scenario and propeller structure.

Blade shape: the shape of the blade has an impact on thrust, efficiency and noise, etc. The shape usually used is trapezoidal, triangular or rectangular. The formula for calculating the blade area is

A = F / (ρ * u * (1 - σ))

Where, A is the blade area, u is the linear velocity of the blade, σ is the propeller slip ratio.

Cross-sectional shape: The cross-sectional shape includes blade bending curvature and torsion, and the selection of these parameters needs to consider the hydrodynamic performance of the propeller and noise vibration and other factors.

Pitch: Pitch is the distance propelled by the propeller blade rotating one week along the axis direction, usually the choice is equal pitch or variable pitch.

3、Noise and vibration

Noise and vibration are important factors to be considered in propeller design, and the propeller structure can be optimized by

Reduce the thickness and pitch of the blades, increase the number of blades, change the shape and angle of the blades, etc.

4、Material and manufacturing

Propeller materials and manufacturing processes have an impact on the performance and life of the propeller. Usually the materials used are carbon steel, stainless steel, aluminum alloy, etc., manufacturing processes include casting, forging, cutting, etc.

**Ⅲ, the details of propeller design**

In the calculation formula of blade area, F is the required thrust, which needs to be calculated according to the mass and speed of the ship. And the linear velocity u of the blade can be calculated by the following formula:

u = π * D * n / 60

where D is the diameter of the propeller and n is the speed. It is important to note that when calculating the blade area, the thrust is distributed to the individual blades in proportion to each blade.

The slip ratio σ of the propeller is the ratio between the actual propulsion distance and the theoretical propulsion distance, which is usually between 0.05 and 0.2. The slip ratio is calculated by the formula

σ = (n * D - V) / (n * D)

where n is the rotational speed, D is the propeller diameter and V is the boat speed.

The twist of the propeller is the degree of twist of the propeller blade, which is usually used as linear twist or secondary twist. The twist angle is calculated by the formula

θ = 2 * π * r * tan(φ) / p

where r is the blade radius, φ is the twist angle and p is the pitch.

The drag coefficient C of a propeller is the amount of drag per unit area, which usually needs to be determined by experiments or simulations. Commonly used calculation methods are turbulence simulation, wind tunnel experiments, etc.

**Ⅳ, some considerations of propeller design**

Propeller diameter and number of blades need to be determined according to the required thrust. Too small a diameter will lead to insufficient thrust, too large a diameter will increase the hydrodynamic drag and manufacturing costs. The number of blades needs to be selected taking into account factors such as clearance between blades and drag. Generally speaking, the higher the number of blades, the stronger the thrust, but it will also increase noise and vibration.

The blade shape, cross-sectional shape and pitch need to be selected according to the required thrust and hydrodynamic performance. Different blade shapes and cross-sectional shapes will have an effect on thrust, efficiency and noise, and different pitch will have an effect on the speed and efficiency of the thruster. When choosing the blade shape and pitch, the relationship between different factors needs to be considered and the best parameters are determined by experiments or simulation calculations.

The slip ratio of propeller refers to the sliding phenomenon of propeller blades due to fluid resistance during travel, which is also an important factor affecting the efficiency and thrust. The optimal slip ratio needs to be determined by experiments or simulations during design to achieve the best performance.

Propeller manufacturing and installation requires attention to quality and workmanship. The propeller blades need to be precision machined and balanced to avoid noise and vibration. During installation, attention needs to be paid to the clearance and alignment between the propeller and the hull to ensure that the propeller can operate properly and provide sufficient thrust.

**Ⅴ，Some optimization methods of propeller design**

Blade shape optimization: By optimizing the shape of the blade, the efficiency and thrust of the propeller can be improved, and noise and vibration can be reduced. Commonly used optimization methods are multi-objective genetic algorithm, artificial neural network, etc.

Cross-sectional shape optimization: By optimizing the cross-sectional shape of the blade, the hydrodynamic performance and noise and vibration characteristics of the propeller can be improved. Common optimization methods include CFD simulation, turbulence simulation, etc.

Pitch optimization: By optimizing the pitch, the efficiency and speed of the propeller can be improved, and the noise and vibration can be reduced. Common optimization methods include variable pitch design, pitch segmentation design, etc.

Material and manufacturing optimization: By selecting suitable materials and manufacturing process, the manufacturing cost can be reduced and the reliability and service life of the propeller can be improved. Common optimization methods include material selection, precision machining, etc.

**Ⅵ，Some future directions of propeller design**

Intelligent design: With the continuous development of artificial intelligence and big data technology, propeller design can achieve more accurate and efficient design through intelligent algorithms and data analysis to improve design efficiency and performance.

New material application: With the continuous development of new materials, the choice of propeller materials will be more diversified, such as carbon fiber composite materials, titanium alloy, etc., to improve the strength, stiffness and corrosion resistance of the propeller.

Full flow field optimization: With the continuous development of computer simulation technology, the propeller design can be optimized globally by full flow field numerical simulation to improve the efficiency and performance of the propeller.

New propeller structure: With the continuous development of ships and underwater equipment, the research and development of new propeller structure will become an important direction for propeller design, such as water jet propeller, magnetic levitation propeller, etc.

**VII. Some environmental directions of propeller design**

Reduce noise and vibration: The noise and vibration of propellers have an impact on marine ecology and human health, so it is necessary to reduce noise and vibration by optimizing the design and manufacturing process.

Reducing emissions: Propellers generate exhaust and waste water when propelling ships and underwater equipment, and need to reduce emissions and protect the marine environment by optimizing design and using environmentally friendly materials.

Improving efficiency: The more efficient a propeller is, the more it reduces energy consumption and carbon emissions, so it needs to be optimally designed to improve efficiency.

Microbial antifouling: The propeller surface is prone to marine life growth, which can affect the efficiency and performance of the propeller, so this needs to be addressed through antifouling coatings and microbial antifouling technology.

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