puffers & vics

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puffer engines

The earliest puffer engines, such as the one which powered the 1856 "Thomas" were simple single cylinder non-condensing units and would have looked very much like the one in the mid-19th century drawing below right, although this particular one appears to probably have been for industrial rather than marine use.

These engines exhausted the used steam after each power stroke directly from the cylinder up the funnel to atmosphere, the distinctive sound of which gave rise to the name "puffer",   This wasn't a problem as, as these vessels operated on canals as opposed to the sea, they had an unlimited supply of fresh water to keep them going.  The name "puffer" was to attach itself to a whole genre, even when in later years they were fitted with condensing compound units, and laterly with diesels!

Initial forays by vessels powered by these engines into the salt water of the Clyde soon led to the appreciation that salt water and boilers did not mix: the salt and other minerals in sea water quickly led to the boiler tubes clogging up with the resultant risk of them exploding, which a few did and sometimes with fatal results for the puffer's crew. The "quick-fix" was to regularly flush the boilers through with fresh water but this was clearly not a long-term solution.

This led to the compound two-cylinder condensing engine being adopted as standard. A much more efficient unit, this engine re-cycled its used steam by cooling it and then returning it to the boiler for re-use. In this two cylinder design the first took the high pressure steam directly from the boiler usually at in excess of 100 psi, and then exhausted it to the second low-pressure cylinder, at around 30 psi, which extracted most of the energy left before it exited the spent steam to the condenser.  The fact that steam condenses into a very much smaller volume of water creates a vacuum on the outlet side of the lp cylinder and this also delivers additional power. The picture below is of a typical two-cylinder compound marine engine, although probably somewhat smaller than those used in puffers. The smaller diameter HP cylinder is left of centre, steam exhausted from it is fed by the pipe running lower left to upper right to enter the low pressure cylinder before being exhausted to the condenser via the pipe pointing at the camera.

It is interesting to note that the wartime development of the puffer, the Ministry of War Transport's VICs, were powered by two cylinder compound steam engines although by this time the diesel had become the norm for vessels of their size. The reason for this is actually quite simple: in engineering terms the steam unit itself was simple. In other words it could be built in low-techology factories, as opposed to the much more sophisticated engineering required for internal combustion engines. A few VICs were built with oil-fired boilers rather than coal burners, including VIC56, but accurate records of which others are sparse. . Only seven late-build "Improved VICs" (79, 80, 101,102 and 103 by Richards of Lowestoft and 105 & 106 by the Shipbuilding Corporation at Newcastle) were diesel powered from new. A good description of the development and operation of steam engines is given in Wikipedia

After the war many of the pre-war Clyde puffers as well as some of the surviving VICs which had migrated north to the Clyde were re-engined with diesels, for the most part from the Kelvin company. Some puffers however continued in steam power well into the 60s. The diesel conversion, by freeing the space taken up by the boiler, also allowed a roomier superstructure and improved crew accommodation to be incorporated. At the same time the trademark tall slender puffer lum for'ard of the wheelhouse became squatter and moved aft allowing the helmsman an unobstructed view ahead.

Paul Hunter, a regular contributor to ClydeMaritime, has kindly supplied some photographs taken by himself of VIC32's engineroom as it is in 2013. The engine is the original and the boiler an exact replica
Photographs copyright Paul Hunter 2013

of the original. Click on the thumbnails below to see larger copies.