By ROBIN BAILEY



Two Aucklanders, each with a passion for yachting, an engineering background and a talent for lateral thinking, have made a breakthrough in the specialised field of marine propulsion.



Bryan Bartley and John Blundell have developed and patented a new form of self-feathering propeller for yachts from 20ft to 40ft powered by motors from 10hp to 50hp.



The pair began work on the propeller eight years ago after deciding there had to be a better way than the existing geared feathering prop.

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They experimented with variations of today's prop by testing them on their own yachts before coming up with the composite-bladed version that is now on the international market.



With their Kiwi Feather Prop the blades are free to follow the water flow, acting like underwater weathervanes. Geared feathering propellers line up with the drive shaft, which may be 15 degrees or more to the water flow. If one blade turns to the water flow, the other turns against it through the gearing, creating auto-rotation and increased drag.



The blades of the Kiwi prop are made of a tough modern composite material similar to that used for the props on high-performance 250 hp outboards. Because this material has a similar density to salt water it is almost floating, making the blades responsive to changes in the direction of water flow.



The inventors say one of the main advantages of their simple and robust system is that it does not require expensive sets of machined bevel gears and small bearings which are characteristics of other geared feathering propellers.



Bryan Bartley: "There is no corrosion because our composite blades are not big electrodes as are other propellers, but are insulators. Also the pitch is easily adjusted using an Allen key with the prop installed so it can be fine-tuned for maximum performance. This aspect is so simple it can be carried out by mask and flippers with the boat in the water."



He adds that there have been no structural failures on any of the propellers installed so far and like John Blundell he is confident the test programme they have carried out and the number of Kiwi props now in service means that their reliability is proven.



Protecting their intellectual property has cost the inventors more than $40,000 so far and the Kiwi prop is patented in the United States, Australia and New Zealand, which they see as the main markets. They plan to extend coverage to Europe as the marketing programme develops.



The feathered prop won an inventors' award at the 1994 New Zealand Easter Show which helped move the invention into sales mode. Blundell says word of mouth among the sailing fraternity, coupled with a modest promotional campaign in the boating press has lifted sales of the prop by around 400 per cent a year. And like many other manufacturers of specialist products the internet has proved a useful sales aid. Their www.kiwiprops.co.nz site has helped spread the word worldwide.



Dennis Craig, from the Engine Room at Westhaven in Auckland, has played an important role in getting the Blundell-Bartley invention into the marketplace. From his perspective, the secret of its success is simple.



"I was introduced to the prop by John, who is an old yachting mate," Craig says. "We had sailed together years ago in 18-footers and in M-class before we both progressed to grown-up boats, so it was logical that we kept in touch during the development of the Kiwi prop.



"Our company had been selling and fitting European feathering props for years. These were both excellent and expensive. The local product proved equally or more efficient and with the imports retailing at around $3500 and a comparable local three-bladed version at $1800, our cost-conscious New Zealand clients took little convincing."



Price will no doubt also be the deciding factor in potential markets internationally.