Trevithick Dredger Engine. The Dredger
by John
I have no intention of modelling the dredger, but in making decisions about the engine base have gone back to the sources to find out about the gun ships. These are referred to as “gun brig”, “bomb-ship”, “hulk of a dismasted ship”, in letters by Trevithick and others.
The first three of these dredgers were recorded by Trevithick as being 80, 120 tons and 300 tons.
This diagram is probably of the dredger “Blazer”, with a 6hp Trevithick engine powering the bucket chain and winch. The cylinder diameter was 14.5″ and the stroke was 4′. Trevithick recorded that his dredger would lift 100 tons of mud per hour. Rock and gravel 180 tons per 6-8 hour tide. It must have been impressive enough for him to obtain a contract to lift 500,000 tons per year from the bottom of the Thames at 6 pence per ton. Other dredgers had Trevithick engines of up to 20hp. (ref. “The Life of Richard Trevithick” by Francis Trevithick 1872)
Magnified view of the engine house on the dredger. Note the relative sizes of the flywheel and the bucket chain driving gear.
And this is the diagram of a cross section of a bomb-vessel from a century before Trevithick. It is mounting a 13″ bore mortar. Note the massive supporting beams. You can see why Trevithick chose this type of vessel to mount his steam engine and dredging machinery. 
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