The building of a replica 1898 Nathanael Herreshoff triple expansion steam engine – as told by Chris McMullen.
The Herreshoff engine is a triple expansion type with cylinders 3-1/2” x 5”x 8” with a 4-1/2” stroke. It is a smaller version of that depicted in the L Francis Herreshoff book ‘The Wizard Of Bristol’ page 228.
The engine is very different to what the textbooks on the subject show. Everything designed by Nathanael Herreshoff seems to be that way. He certainly never copied traditional thinking but worked it out for him self.
Those interested may notice the two crankshafts gear driven one to one. The right hand one drives the piston valves. Going astern is effected by sliding bush or sleeve within the driven gear activated by a lever, this rotates the valve C/S to a new position. The bush, gear and shaft required machining male and female three start threads, left and right hand 8” pitch! Not easy. The threads have / had to be cut on a planer using a dividing head coupled to the motion. Modern cars use a camshaft driven by a timing belt, similar to Herreshoff but remember this engine was designed in 1898! The engine is very short to allow the crankshaft to be supported by two bearings and also to prevent loss of heat as the exhaust steam travels from one cylinder to the next, thus trying to reduce pressure loss.
If you look at the image of the crankshaft casting (below) you will notice the overhung balance weights. Notice the lack of material in the web between the second and third journal. The crank can’t be ground and there is no easy way to machine the metal designed to be eliminated by casting. Casting this crank was a mission in SG iron. To cast it in steel (with 1/4” to the foot possible contraction) is going to be more difficult to achieve the correct length.
H.M.C.O had an outside foundry cast their steel but I notice in reading a recent article on Herreshoff Anchors they did have problems with their steel castings.
The base of the engine is a bronze casting to hold oil. The engine max revs are about 700 so the engine will have to be enclosed or throw oil everywhere.
There are good drawings available for this engine but no tolerances are given. I guess the fitters knew what was required. The original drawings were coloured to show the different materials, as was normal drafting practice. The prints I got were black and white and difficult to read. No layers as in CAD drawing.
The Boiler is a three-drum type with curved tubes. It is similar to a Yarrow Type boiler. All the circulation is achieved in the tubes, the outer tubes being cooler than the inner. Once the circulation starts it continues. This was proven by Yarrows experiment in the early 1900’s. So Herreshoff and Yarrow, an ocean apart, came to similar conclusions. The upper drum of the boiler is 8“ OD, the lower drums 4-1/2” all with 5/16” wall. The 1/2“ tubes are expanded. Not easy to do up a tube just over 4” ID.
The boiler was built under survey. The working pressure is 250 PSI.
There are no pumps on the engine. The boiler is fed and the cooled exhaust condensate is removed for reuse by an independent steam driven combined feed and air pump. These pumps were the only item on the launch not made in house by H.M.C.O. There were no drawings of these Marsh Pumps made by The American Steam Pump Co., Battle Creek Mitch. I copied mine from ‘Vapo’, an incredibly clever but simple pump with two moving parts but very difficult to manufacture.
I should add there has been no fabrication. Everything has been cast in iron or bronze.
Again this interesting project has been done for no other reason than for my own personal satisfaction. I guess Prof. Evers Burtner’s comments (see copy of magazine article below), I quote “It is too bad that this engine is so complicated that amateurs would not be tempted to build one of their own”, was red rag to a bull.
To view part one i.e. the boat click here https://waitematawoodys.com/2014/07/07/chris-mcmullens-herreshoff-steam-launch/
Click Any Image / Photo Below To Enlarge
LFH 1970’s Letter1
LFH 1970’s Letter2
Evers Burnter article1
Evers Burnter article2
Simpson Strickland Steam Launch
Herreshoff Steam Launch
Orginial Herreshoff engine
Orginial Herreshoff boiler
McMullen Engine cylinder & moulding 1987
McMullen replica
Crankshaft casing
McMullen replica
Vapor as found by Chris M
