New Axiom Propeller to Help Cut Shipping Costs
Fri, 21 September 2012
With fuel costs spiralling and increasingly stringent environmental regulations affecting marine communities globally, the need to conserve vessel energy is an ongoing consideration for ship and boat operators.
In addition to lighter ship construction techniques, utilisation of composites and fuel monitoring systems, many players in this sector are reassessing their propulsion arrangements in recognition of the key benefits that optimised propeller forms can deliver towards this end.
One company which has been developing radically redesigned blades in its range of propellers designed to dramatically reduce fuel consumption is Northamptonshire based Axiom Propellers owned by Alan and David Watts.
The first Axiom propeller – unique for the fact that there is no twist with regards to pitch and the propelled race is cylindrical in its form in direct contrast with the marine screw - was launched at METS in 2008.
Since the propeller was first launched, around 700 vessels have been fitted with an Axiom, with inland vessel owners comprising a major chunk of Axiomʼs customer base.
Four years on and the company has added further propellers to its range – the latest is the DWS-type propeller suitable for yachts, work boats and shipping up to 150ft.
Extensive cavitation tunnel testing has been carried out at the Emerson facility, Newcastle University and sea trials are currently ongoing.
So far this latest propeller has been fitted to half a dozen vessels with ‘phenomenal’ results.
One vessel currently testing the DWS is the Plymouth Pilot Bumbly II operating on a daily basis in the Felixstowe area, with significant benefits reported by the vessel’s pilots including lower wash and wake with acceleration and top speed improved compared to a typical Archimedean screw. Slow speed manoeuvrability is also better with a tighter turning circle and precise astern performance.
Bollard pull trials have also been conducted pitching a quality screw against an Axiom DWS resulting in an eight per cent improvement for the latter which if fitted within a Kort type nozzle, would also give further improvements. Devices used before and after a screw propeller such as ducts, spoilers and rudder-bulb fins which straighten out the water flow are not needed when fitting an Axiom propeller.
“The DWS prop is the result of many years of research and development and is designed specifically to have improved performance together with better handling and stopping. The prop is unique in its blade symmetry, giving equal thrust ahead and astern, never before achieved with marine propellers.” said David.
“Over the last four years we have been perfecting our propeller techniques allowing Axiom to expand into different markets. No-one has produced anything significantly new for many years. There have been small innovations, but nothing on the scale of the DWS propeller with its completely redesigned blades.”
He added: “A marine screw moves 15 per cent more water than it needs to due to induced rotation, which is pure waste.
“Due to its blade shape, with no pitch, the four quadrant data of the DWS is uniform, resulting in equal, smooth thrust leaving the blades, removing the need to fit energy saving devices that straighten out the water flow before and after the propeller. Slip has been reduced giving improved and more economic passage times. Less wash is produced and there are enhanced handling and stopping characteristics.”
His comments are backed up by cavitation tunnel and open water testing, both providing proof that the Axiom prop has equal thrust ahead and astern due to its blade form with ʻsymmetric characteristics in almost all quadrantsʼ.
Compared to a screw propeller, the Axiom provides immense benefit to shipping through a huge reduction in induced and axial rotation. With a conventional screw, Negative Slip moves more water than is actually needed to propel a vessel, wasting the energy which goes into rotating the water instead of accelerating it.
The propellers are made, in the main, from AB2 (a form of NiAIBr). They are designed to fit conventional shaft and pod arrangements, with controllable ʻpitchʼ, feathering and folding types in development. Engine horse power and revolutions per minute are controlled by the overall diameter and the angle of attack (shear) of the blades.
The Axiom DWS is available in two, three and four blade forms and gives vessels the ability to maintain a faster average speed, even in adverse conditions, thus reducing passage time and providing an immense benefit to shipping. Reduced propeller slip reduces fuel usage by five to eight per cent.