Propulse AB

Starrmyrsvägen 13, 184 91 Åkersberga

Telephone +46 85 4401300
Fax +46 85 4401310

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Our range of products

Product categories

  • 02  Engines and Related Equipment
  • 02.02  Engine Parts/Control
  • 02.02.12  Propellers


Our products

Product category: Propellers

Propeller school

Here we explain the common propeller terms, their shape and how they work. There is a lot of literature to be found on propellers for those who want to go deeper into the subject, but we intend to keep it simple for the layman to understand.

Generally about propellers
Although a propeller is sometimes called a screw, it does not work like one. The propeller blades are shaped like wings and rely on the three crucial properties, pressure thrust and resistance. The blades are mounted onto a rotating hub where the thrust draws water upstream and then throws it downstream of the boat’s wake. Newton’s third law of “action and reaction” makes the boat go forwards.

The pitch is the distance that the propeller would travel in one revolution if there were no “slip”. The pitch is measured in inches and is determined by the angle of the blades. It should be noted that the pitch may not be the same throughout the blade. Since it is the pitch that provides the propellers drive, it is not unusual for the pitch to reduce at the root of the blade as the oncoming water has lower velocity at the hub.

Number of blades
Most propellers on the market have 2, 3, 4 or 5 blades. More blades for better grip in the water, but this also increases the resistance. Two blade propellers are used for lower horsepower motors. Three and four bladed propellers are the most common for pleasure boats, whilst five blade propellers are used for sports craft such as wakeboarding and water skiing as they are considered to provide a better wake to ride on.

A common way to adjust the metal propellers when applying a so-called cup on the blade trailing edge. That compares with a small flap on the trailing edge of an aircraft wing. It gives the blade pitch increases, but also under the pressure of the blade leading edge spread out a bit and can in this way prevent cavitation.

To get your new propeller blueprinted you send it back to the manufacturer or a propeller specialist who performs fine adjustments to the form as it have been stated in the manufacturing drawing. This is mainly valid for propellers made of metal. Deviations in the shape of the blades and angles are from the manufacturing process where as always occurring tolerances. Typically, these tolerances are within an range that works just fine for normal performance and usage.

The diameter of the propeller is measured in inches and is a circle formed by the tips of the blades as the propeller rotates. (1” is 25.4mm) Most propellers are marked diameter x pitch (for example 13” x 21”)

Rake is the angle of the blades on the propeller shaft and is designated as positive aft. A rake shape the blades into a cone and ensures that concentrate the water jet, as it prevents water from leaking out radially. Especially for surface-piercing propellers have a positive effect. In some contexts pushed the bow of the boat upwards with increasing rake. A sheet may have progressive rake also can rake cuppas.

As the previous discussion, it is the lift of the airfoil that provides the propulsive force, while the resistance requires enginepower. There are however, a characteristic of airfoils which may be used to maximize the efficiency and it is having the right angle of attack to the water. For a given speed and rpm is the propeller pitch which should be amended to obtain a more economical propulsion.

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About us

Company details

We design all of our propellers inhouse. The company is entirely Swedish and production is performed in carefully selected suppliers, primarily in Sweden to have close contact and monitor the high quality standards we impose on them.

Our propeller design is based on a 4-blade design in which first of all the blades are adjustable to different pitches, but also replaceable in case of damage. The parts are molded in a fiberglass-reinforced polyamide, which is an accepted substitute for cast metal, mainly aluminum. The products are best suited to the market for outboards in the range of 20-300 hp.
The company was founded in the late 90s around an idea to create an adjustable propeller of composite materials. The benefits would be many if the blades could be adjusted without either switching hub or blades. Furthermore, there was a desire to use a plastic material that can be molded and also resist corrosion, etc. The basis for the design came from a long experience of production of pleasure boats in plastic. Tests for a variety of design options were taken, all to ensure a sustainable and reliable product. The raw material was selected in consultation with suppliers who have extensive experience from products in both aerospace and the automotive industry, where price and performance, but not least, high technical standards is an everyday reality for the finished product. Now, here a little over 15 years later and with many props around the world in all the waters, we know that the concept works.

The brand and product
Propulse stands for innovation and creativity in an otherwise relatively conservative navy technical environment. We are, to our knowledge the only company in the world that manufactures and markets a propeller where the pitch can be adjusted and the blades can be replaced. We are constantly working towards improving the quality of the product and refine its design and choice of materials, all to achieve better performance in the water.

The material we use is a high performance polyamide, injection molded under high pressure and temperature. To obtain an even stronger material it is reinforced with glass fiber. Overall, therefore, our propellers just as strong as propellers in aluminum and usually better. If we take into account factors such as weight and performance against corrosion etc. it widely exceeds the properties of aluminum. The polyamide are known to be resistant to commonly used chemicals and petroleum products. If necessary, the propeller can be painted with the most commonly available on the market 1 – & 2-component colors.

We decided early on to use only 4-blade propellers as we know they deliver the most interesting performance to the ordinary boat owner. With the manufacturing process we have, all the blades of the same size are made in the same mold. This keeps the weight difference between the various individual blades of the same type to be almost negligible. This, together with the 4-blade design, results in an extremely well-balanced propeller, which most metal propellers have difficulties to demonstrate.

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