New Technology for Naval Propellers

Partnership Secures Strategic Defence Contract

When VT Group won a £200 million contract to provide design and other support services for the manufacture of three Super Vita-type fast attack missile craft for the Royal Greek Navy, at the Elefsis shipyard near Athens, Andrew Smith, Managing Director of F. Bamford & Co. Ltd., in Stockport, recognised an opportunity for his company.  Bamfords have been manufacturing propellers, shafts and stern-tubes for the marine industry for over 100 years, but now specialise in high accuracy propellers for fast patrol boats and precision turning of long, thin shafts to suit. Total group employment is 39, with just 4 people engaged in marine propulsion.  With such a large project, competition with the other major manufacturers of propulsion systems worldwide was fierce.  However, combining the company’s knowledge of the product characteristics sought in this specialist market with Cti’s ability to develop and apply technology in a practical way, provided sufficient competitive advantage to justify bidding for the work with a hope of success.

Fixed-pitch propellers are the most commonly adopted system for high-speed naval vessels and, in this particular case, propulsion is achieved by coupling four fixed-pitch, nickel-aluminium-bronze propellers to each vessel’s main engines via its transmission and shafting system.  Balance, low vibration and maximum propulsion efficiency are clearly vital and can only be achieved with propellers of consistent blade-to-blade dimensions and precision of form.  Traditional casting manufacturing techniques cannot readily achieve the quality attributes necessary to satisfy such demanding service requirements.


However, in 1998, Bamfords was involved in a European project managed by Cti with the objective of developing a fast, cost effective technique for the precision manufacture of prototype, one-off or small batches of castings.  Their intimate awareness of the resulting technology – now known as the Patternless® Process – provided them with the confidence that it alone could produce castings accurate enough for these highly-loaded, high-speed propellers.  Furthermore, Cti had the capacity, in the form of a new, large, high-speed machining system which was installed specifically to enable small companies such as Bamfords to exploit a technology that would otherwise be inaccessible to them.  With a working envelope of 3.6 x 3.6 x 1.2m, and the continuous 5-axis machining capability necessary to generate the complex geometric profiles, this facility helped Bamfords to secure the order to supply the 12 propellers and shafting systems.

clip_image010_000Andrew Smith attests: “without Cti’s practical experience in the application of this technology, and the availability of fully operational, production-scale equipment, we would not have won this export order, so severe was the competition.  The first four propellers confirmed that the process could deliver the very precise castings required to produce extremely accurate propellers, and, as a bonus, considerable cost savings are possible – for example, the machining stock was reduced from 8mm to 3mm.  The order, in excess of £550k, represents 40% of our turnover and the facilities at Cti enabled us to minimise risk by preserving our working capital to such a degree that we only needed to make a minor investment for cutting tools, etc.  This is essential when a small company like ours takes on such a large-scale, long-term project. Without this order we would have had to downsize by a couple of jobs, whereas we actually recruited two operators.  Having access to cooperative facilities like this manned by personnel who can respond practically to our needs, and those of our customers, is immensely valuable and I am confident that this partnership will generate future business for us.  Cti has taught us the value of co-operative R&D; while we can’t conceivably afford to do it alone, we have gained immense value from the project in which Cti developed the Patternless®  Process.  We therefore jumped at the chance to be a partner again in a new European Craft project organised by Cti, called FASTCAST, which aims to extend the technology to complex castings required by sectors such as energy generation”.


clip_image011_000Sean Bianchi, Senior Hydrodynamicist at VT Group, says:  ”When Bamfords first proposed the new process for mould generation, I was very interested in the concept. For a ship to carry identical propellers was, in reality, quite novel. The normal manufacture of a set of propellers invariably results in slightly different geometries. In certain circumstances this results in varying power absorption, thrust generation and, in extreme cases, erosion.

The new Patternless® Process, although quite challenging in the early stages of the contract, has resulted in extremely accurate propeller castings.  When up to full operational capacity, propeller moulds can be manufactured in short timescales with an accuracy not achievable by conventional methods.

The first ship set of four propellers have recently undergone an extensive series of sea trials and have performed as per our predictions.  I have no doubts that this is the way forward and that Cti, through their investment, will be the benchmark that all propeller suppliers will strive to equal”.