This project grew from an original propeller for a small 19th century steam launch acquired at an antique sale in San Francisco in 2003.


8m long by 1.3m beam (max), it is of the style used in the 19th century on the Great Lakes (the curved-over prow is an adaption favoured for where floating ice can be encountered). It was built for me by Nop Velthuizen from Holland using glass fibre/epoxy over poplar strip planking. In return, I'm to supply the engine for a similar boat to be used on the canals there. The patterns and formers for this hull are in Ashburton and may be borrowed.
Piwakawaka under stirling power
Piwakawaka under stirling power


Stirling cycle engines use a closed cycle in which a quantity of working gas (air in the case of Stirling cycle air engines) is alternately heated and cooled. Combustion is external.
They are named after Robert Stirling, a Scottish Presbyterian minister who built (and patented) various versions from 1816. Air engines had been built before Stirling, but he is credited with developing the key elements that almost all 19th, 20th and 21st century examples still share. Stirling cycle engines have had brief bursts of popularity- like when not requiring boilers was an advantage for fractional horsepower engines against steam engine competition in the late 19th century- but have yet to establish any mainstream application. Being external combustion engines (and therefore able to use any heat source) and because of their theoretically excellent efficiency (difficult to achieve in practice though), they're an Engineers dream- and an Accountants nightmare - for 200 years, and still counting.

Click image to watch movie on You Tube
This engine is the 4th in a development series built since 2006 specifically for Piwakawaka.
It's gas fired, 2.5litre swept volume, uses unpressurised air as the working fluid, and is a 'beta' layout with cylindrical heat exchangers. It's first run in Piwakawaka exceeded 5knots, a useful improvement over earlier engines in this series and up with all known benchmarks.
It's designed to be built using average engineering skills and a minimum of equipment (cut-off saw, lathe, drill press, tig welder). And, not that this was a particular goal, it is entirely constructed of found and recycled materials; the rings are from old brake discs, the stainless steel is recycled from urinals and the displacer rod (hard chrome plated) is from a gas strut.

Anyone who wishes is welcome to copy it- I'll help with reasonable support and advice.
I do intend to prepare full drawings and instructions after another prototype or two.
These will be available here at peterlynnhimself.com

Peter Lynn, Ashburton, New Zealand, March 2012

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