Propeller FAQs

  • What is a propeller and what is its function?

    Propellers are sometimes colloquially referred to as ‘screws’, and that’s because at a basic level, they are the same thing. Like a screw is pushed into a wall by a helical thread turning clockwise, a propeller has radiating blades coming away from a central rotating base which are pitched at an angle which dictates how quickly it moves when you turn it. A basic law of physics proposed by Isaac Newton is the idea that if you want to move forward, you have to push backwards. Propellers work because of this principle. A propeller’s turning motion produces a difference in pressure between the front and back surfaces of its blades, also known as thrust. This drives the propeller through the water in the case of marine propellers.

  • What makes a good propeller?

    There are many factors to consider when creating the perfect propeller for a particular vessel. The metrics typically used to assess the functionality and quality of a propeller are: the top possible speed; efficiency in fuel consumption; how long it lasts before needing to be replaced; noise emissions; amount of vibration; and the likelihood of cavitation.  Every CJR propeller is designed to the highest quality standards and custom-made for the specific vessel in question using advanced design and production technology to do so. CJR’s 80 years of experience mean our propeller manufacturing process is fully optimised to extract the best possible outcomes from these quality metrics.

  • What is cavitation?

    Cavitation occurs when at low-pressure, vapour bubbles form in a liquid. It causes major erosion to marine propellers underwater and subsequently, a reduction in efficiency, and an increase in noise and vibration. Cavitation can be avoided from the point a propeller is designed by fully analysing and optimising a propeller’s pitch and flow velocity to align perfectly with the vessel.

  • What is the history of the propeller?

    Arguably the first iteration of the propeller in recorded history is Archimedes’s screw in approximately 200 BC which was essentially a rotating spiral used for water irrigation. The first time the propeller was properly introduced to the marine industry as an alternative way of powering vessels wasn’t until the 1830s when two inventors working in Britain, John Ericson and Francis Pettit Smith demonstrated the effectiveness of steam-propeller fueled vessels and they were subsequently adopted by the British navy and the global commercial marine industry by the mid nineteenth century. One of the early iconic iterations of steam-propellers in action was Brunel’s SS Great Britain.

    Innovation in the field of propeller design largely stagnated until the fuel crisis of the 1970s when steam was phased out in favour of the more efficient diesel engine-fuelled propellers.

    CJR entered the scene in 1948 and has been a force for innovation in propeller manufacturing ever since. Over the last 5 years, CJR has pioneered the fastest turn-around for bespoke propeller manufacturing in the industry. Its four-million-pound investment in its design and manufacturing facilities include combining CFD with advanced ‘patternless’ robotic mould making, multiple 5-axis CNC machining centres, and the production automation technology required to tie every step of the process together.

    For a more detailed history of the propeller from Archimedes to CJR, take a look at our propeller history timeline.

  • How long does it take CJR to manufacture propellers?

    CJR Propulsion is one of the world’s most respected marine propeller manufacturers. Our emergency boat propeller replacement service can provide our clients with an identical copy of their propellers in as little as two weeks*. Our rapid propeller replacement service has been specifically developed to meet the needs of yacht charter businesses, boat owners, and new build and refit boat yards, who need a high quality but timely solution for damaged or broken propellers, or those experiencing propeller performance issues.

  • What's the difference between aeroplane propellers and marine propellers?

    Aeroplane propellers have thick and narrow blades that turn at high speed, whereas ship propellers have thinner, broader blades that spin more slowly. Ship propellers also work most efficiently in water at lower speeds because of the difference in density between water and air (about 1000 times more, in fact). Therefore aeroplanes need to move a lot more air then marine propellers need to move water to produce the same amount of momentum.

  • What does ‘props’ mean?

    ‘Props’ is a shortened version of ‘propellers’. Other colloquial terms for propellers include a ‘screw’.

Rapid Design and Manufacturing for Propellers

CJR has recently launched a rapid turnaround service offering bespoke, fully optimised Class-S propellers in just 14 days or less. Designed for propellers up to 1500mm in diameter, our replacement propeller services can save as much as three months from the typical replacement timeline. For more information, visit our dedicated Rapid Turnaround page.

3D scanning and reverse engineering

Replacing a single damaged prop is now significantly easier, quicker and more cost-effective with CJR. Our ability to 3D scan and reverse engineer any propeller to the highest degrees of accuracy is yet another reason to choose CJR. For more information, visit our dedicated 3D scanning page.

Get in Touch

CJR combines decades of experience with continuous investment in the latest technology and engineering prowess. Just drop us a note to find out more about how we can help you.