With the overall idea in his head he began to sketch out an engine design, which was built into a prototype and exhibited at the Hutchwilco Boat Show and is now on display at Motat.
The Shepherd Engine is an axial sleeve diesel engine. It inverts the core motion of the combustion engine and has fixed pistons and reciprocating cylinders converting linear motion into rotary motion without the use of a crankshaft.
The advantage is that it produces greater power, is cheaper to run, environmentally cleaner and cheaper to build.
The problem for Shepherd Engine Ltd is a ubiquitous one: finance.
Shepherd is convinced that the engine will revolutionise everything from manufacturing in New Zealand to motor vehicles. He just needs the money to build an updated prototype and move forward.
The first round of funding came from friends and family and paid for patents.
The company has decided to issue shares, which will be offered to the public this year.
Pat Castle, a lawyer who runs Propel, a company that specialises in assisting innovators, says the first round of funding for inventors is usually from what he refers to as "friends, family and fools".
The next stage, says Castle, is funding from "propellers" who assist inventors with finance and mentoring.
"When the invention is validated further it would be referred to a professional angel investor, or in some cases [business incubator] the Icehouse."
Not all inventions are born in garages. Most universities have the machinery in place to incubate inventors and their products and are a hotbed of innovation.
One university-based product is a garment for measuring the wearer's respiratory rate developed by Footfalls and Heartbeats, which emerged from AUT's Textile and Design Lab.
The garments have conductive yarns that measure the wearer's respiratory rate without the use of obtrusive heart-rate monitors.
Most universities have departments specifically aimed at identifying and commercialising inventions, such as the University of Auckland's technology development department at Auckland UniServices and Victoria University's Viclink.
These departments don't just help university-based inventors, says Steve Corbett, chief executive of Massey University's ecentre. They provide services to members of the community who want to "de-risk" their inventions by getting professional assistance and advice.
Corbett says the ecentre often connects academics and their research capability with the garage inventors who come to it for advice.
The Government also finances research that produces innovation. One scientist who has emerged from that route is Marcus King, who has been "inventing" practical and marketable devices for 27 years.
The Industrial Research Ltd (formerly DSIR) principal engineer doesn't consider his products "inventions". He does practical research using scientific methods.
"It is very well defined how we carry out research," says King.
"Occasionally inventions come out of it."
King's first commercial "invention" was a tractor-driven automated pollination machine for kiwifruit. His other innovations over the years have included devices for primary producers, forestry, and the horticultural industry.
He is now regarded as New Zealand's premier inventor of assistive technology for people with disabilities. He began by working with patients and clinicians at the Burwood Spinal Unit, where he developed rehabilitation products.
His more recent commercial products have been aimed at the 46,000 stroke survivors in New Zealand every year, a market that is also huge internationally.
A number of King's innovations have been patented and developed into products for export and the domestic markets by Wellington medical device manufacturer Im-Able.
King does not seek fame and fortune through his inventions. He's more than happy to receive a salary for doing what he loves, and feel that he is benefiting "New Zealand Inc".
At the other end of the scale, the blokes-in-sheds innovators and inventors can be a little eccentric, Castle admits. But they always need to be taken seriously.
"They can appear quite unusual. They have qualities we can't measure - and faith."
Even if one invention doesn't come off, the next might be worth millions.
Sometimes the problem that an inventor seeks to solve can be remarkably simple, although the answer isn't always. Builder Walter Hensch's clients wanted rounded corners for their internal fit-out, but plasterboard doesn't bend. Fibrous plaster can create rounded corners, but has a different finish.
The breakthrough for the product Roundy was to perfect a curve down to a radius of 200mm without fracturing or cutting the plasterboard, creating a seamless corner.
The rounded plasterboard is now used in a number of commercial and residential buildings and the company he runs with wife Margaret - Corner Solutions International - is in the process of licensing Roundy to manufacturers in Korea and other countries.
