How to choose the right propeller for your workboat or superyacht

The right propulsion system is key whether your priority is achieving optimum speed, improving fuel efficiency, reducing lifetime costs, or enhancing comfort. To help you source the best available system, we’ve put together this quick list outlining what questions you should be asking your propeller supplier.

The propulsion and sterngear package is a major part of every vessel and can significantly impact performance, fuel efficiency, noise and vibration levels, as well as maintenance and replacement schedules. Over the lifetime of a boat, these factors can collectively make a significant difference to the total operating costs, especially for a workboat or charter yacht. So, with seriously big numbers at stake, how do you ensure you’re getting the best available propulsion solution? The answer is to ask the right questions.

It is fair to say propulsion and sterngear systems don’t often get the attention they deserve. They’re rarely top of the list when it comes to specifying a new vessel or choosing a builder but, in recent years, the distance between a leading and trailing propulsion manufacturer has grown dramatically. Today, the difference between a fully CFD-optimised, precision-engineered, CNC-machined system and one built by hand, with little regard for the vessel in which it is installed, couldn’t be more striking. However, you’d be surprised how often the latter is the preferred choice – a decision typically based entirely on price. Unfortunately, this can end up costing a lot more in the longer term.

Props and rudders designed for performance and sustainability

When you think about it, it seems obvious that your new props and rudders should be designed specifically for the vessel’s actual hull form, using the latest computer-based technology to ensure peak performance in a myriad of conditions. It seems equally obvious that the old ‘experience first’ approach is grossly out-of-date and should be consigned to the history books. However, the reality is somewhat different. Many propeller companies still rely entirely on experience and ‘a good eye’ and use a standard pattern they designed ten years ago.

If performance and sustainability are key to your business, it’s vital to ask the right questions when you’re specifying a propeller.

Here’s what I think you should be asking:

1. Will my propulsion system be designed using CFD and flow predictions for the specific vessel’s hull form and known appendages?

If the answer given is no, you should be concerned and should question what their approach is. If all they talk about is experience and hand-finishing, be aware that you may face an increased likelihood of issues with vibration, noise, cavitation and below-expected performance. Each of these issues has the potential to impact enjoyment on board and incur significant costs to put right. The best way to guard against this is to ensure your propulsion system is designed using CFD to Class S specification. It should be designed specifically for your vessel and using the real hull form.

2. Will my propellers be CNC machined and meet Class S standards for optimum efficiency and vibration-free operation? Or are they hand-finished and manufactured to only Class 1 or Class 2 standard?

Class 1, despite its name, is a lower standard, with the potential to cause issues in both the short and long term.

3. How do you predict cavitation?

Cavitation is the erosion of the surface of the props and rudder. CFD analysis is able to predict and minimise cavitation by understanding the flow of water around the propeller and making adjustments to the design to reduce the pressure pulses that cause the issue. If your propulsion specialist doesn’t do cavitation analysis or it is done purely by experience (guesswork), be aware that it may become an issue in the future.

4. What happens if the boat doesn’t perform as I would like/expect?

A professional propulsion specialist should be able to support you through the sea-trial process, including the use of data acquisition tools to gain a detailed understanding of the issues and their causes. They should really care that their product isn’t performing and be keen to put it right.

5. How quickly can I get the propellers?

Time out of the water costs money. Whether you’re looking for a replacement propeller or you don’t want anything to hold the finish date of your new project up, ask for a realistic delivery date. For example, thanks to CJR’s investment in the latest equipment, the two-week rapid delivery service means you can have a Class S prop designed and manufactured in just a fortnight.

Follow the steps above to discover exactly what questions you need to ask to get the best available propulsion system for your boat. You can get more tips and advice by following CJR on LinkedIn. For more information on CJR’s products and services, take a look at the products and services page.