Ships Nostalgia - View Single Post - Doxford Engines 3-legged
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Old 21st February 2012, 17:03
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Duncan112 Duncan112 is offline  
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Originally Posted by Mike S View Post
I was under the impression that the classic Doxford was a victim of it's own design in that the crankshaft was unable to handle the increasing horsepower of it's rivals and they reached the design limit.
Still a wonderful engine and a famous part of maritime history.
That's always been my opinion because there are only 4 ways to increase the power of a reciprocating engine:

1) Increase the cylinder diameter but this increases the distance between the main bearing centres, in the case of a Doxford this distance is already large because of the presence of the side rods and bearings. This would result in the crankshaft bending too much between the main bearings.

2) Increase the piston stroke - this would lead to an over long cylinder liner with associated casting problems, the tripartite liner as an attempt to overcome this was never really successful

3) Increase the mean effective pressure in the cylinder - this would increase the bending moment on the crankshaft - see 1 above

4) Increase the number of cylinders - this would lengthen an already long engine increasing the size of the machinery space and eating into cargo space.

Mind you, material science and technology has come on a great deal in the 30 years since the demise of the Doxford, maybe these problems could now be overcome.

One other problem was the additional survey requirements of the bearings for the side rods, 2 bottom ends and crossheads.
“Those who cannot remember the past are condemned to repeat it.”

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