Triple Expansion
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Build the Elliott Bay Triple

May 18 2018: 

Alloy and Part changes: We have just completed a revision and refinement of the Elliott Bay Triple Expansion Marine Engine castings kit. The CROSSHEADS will now be ductile iron (65-45-12), with toughness that enables lighter weight.  These parts (three per engine) now have less volume, specific machining surfaces, more as-cast surfaces, so they are more like original large marine engines.  Also, VALVE GEAR REGULATOR are also Ductile Iron, and their geometry was changed so their slots are parallel to the DRAG LINKS and so they rest vertically and close to the engine when in Ahead position. 

In addition, the SLIPPERS will now be bronze rather than iron, and, all other sliding and bearing parts will now be cast in a more expensive C905 Bearing Bronze, an alloy that equals SAE 660 alloy properties for the service in this engine, and can be more easily sourced because fewer foundries are capable of casting lead-containing bronzes.  At the same time, foundry mechanization required us to re-mount patterns on more robust boards, which gave us an opportunity to refine some geometries. 

Drawings review: This revision also included a thorough drawings review, made in light of former builders' suggestions and corrections.  The world seems to have fewer "old fashioned blue chip professional machinists and fitters," than when we first offered these castings, twenty years ago.  At that time, one said, "Just send me the castings; the drawings might be helpful; I apprenticed at Yarrow shipyard in 1935; the governor marked chalk on the floor and we knew what to do."  Nowadays, builders depend more on drawings, so, to facilitate:  every part has its own drawing (using ANSI Y-14.5, "Dimensioning and Tolerancing Standards"), and we added assembly drawings, some with notes and narrative to help guide builders who may not have prior experience with marine steam engines, but who want the experience Victorian Era shop practice, then become their own marine engineer.

Cast CRANK SHAFT:  While some builders are accustomed to the complexities of  making a "built-up" crank shaft, and some still may prefer this method, we made tooling for the shaft to be cast in Ductile Iron, which many will find easier to make, either on their own lathe or by sending it out to a crankshaft grinder.  Flanges on both ends of the casting provide holding and center locations for the four axes, the main shaft and three throes.  The abaft flange can be machined as the propeller shaft coupling flange.  A fat section is added to the shaft at BEARING NO. 1 location for the builder to tool thrust bearing RINGS into the shaft (and COLLARS into No.1 MAIN BEARING brasses) if a traditional THRUST BEARING is preferred by the builder, rather than a store-bought-off-the-shelf package thrust bearing. The crankshaft involved expensive patternmaking and its foundry cost is high, so any builders who prefer to make a built-up shaft are welcome to a discount if they do not want the casting.

Cliff Blackstaffe, a marine engineer from the steam age who lived until 1989 told me: "the crankshaft on a shipon which I was Chief was not forged or welded or shrinked, but soft-soldered."  Something to think about!

Spend the same time making a correct engine as an incorrect one. Re-create the established practice of 125 years ago.  The makers of old did not make steam engines the way they did because they knew no better; their methods and materials remain the best way today, with few exceptions.

The engine to the left is the Elliott Bay triple being lowered into the Elliott Bay fantail hull owned by David Porter of Sunset Beach, California.  The boiler (not shown) is a charcoal- fired, ASME Code Elliott Bay boiler which at 40 square feet heating surface pushes the boat at its hull speed of 7 knots.  This particular engine was specially fitted with a Lowe pump for air and feedwater; however, the engine is supplied with castings for air, feed, and auxilary pumps driven from each of the three crossheads.  Cylinder dimensions are HP 2.75, IP 4.375, LP 6.5 and stroke is 4 inches.  Both the HP and IP valves are piston; LP is slide.   Each of the three valvegears has cut-off adjustment, and, the builder has a choice of "split" or "closed" top end connecting and eccentric rods.  The kit consists of 96 castings and 144 drawings. Bar stock and fasteners are not supplied.  Choose WITHOUT crankshaft if you prefer to make a "built-up" crankshaft.  Price $5,600.  Drawings $300.


Triple Expansion Engine Kit WITH Cast Crankshaft         $6,200.00

Triple Engine WITHOUT Cast Crankshaft                      $5,600.00

Drawings Only with USA delivery                              $307.25

Drawings Only with Canada delivery                          $326.90

Drawings Only with delivery beyond USA/Canada     $337.45



Our triple expansion marine engine is a reduced-size replica of engines made for torpedoboats in the 1890s.  We did not simply scale down  dimensions, but we checked original texts used by designers back then to determine cylinder diameters, bearing areas, valve events, etc.  The same part that was a casting 100 years ago is a casting in our kit, and it is made of the same metal.  Here we admit, however, that we have adopted a modern bearing bronze that is resistant to galling with gravity lubrication up to 600 rpm, and we supply bronze stock for you to turn rings.  And, we will substitute aluminum for iron bedplate if the customer wants to save 40 pounds (18 Kg) weight and can get the part deep annodized black after machining. Fifteen of these engines have been or are currently being built in six countries.  Five of these engine are being built in England, the traditional source for small marine steam.

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The Triple Kit's Castings
This photo shows many of the triple kit's castings layed out on a table.  The engine in the background is the same engine pictured above.  In foreground are valvegear bearings and immediately behind are mainbearing caps and boxes (that are fitted into the bedplate); to the Left are two of three bronze pump bodies, and to their right are reversing levers and eccentrics.  In midground are pistons, bottom and top cylinder covers, and cast ductile stock for making rings for all three cylinders and valves (directly behind pumps).

The triple also has independent cut-off adjustment on each cylinder, so the engineer can "take a card" on the engine and balance the work to be done by each cylinder.  I had the good fortune to be tutored by the late Cliff Blackstaffe on the advantages of independent cut-off:  the first launch we built commercially had a two-cylinder compound engine that had gag screws on the weighshaft bellcranks.  It ran "ragged" until Cliff began to work the screws in and out on both valve gears until the engine began to run smooth--even for a compound.  Cliff was one of the last "19th century marine engineers" even though he was born in the 20th.  See his articles in STEAMBOATS & Modern Steam Launches, available from this website, Model Engineer, and Light Steam Power.  Triples are inherently smooth because their cranks are equally positioned at 120 degrees, and the ability to refine cut-off can make them nearly vibrationless.  This triple pushes our 23-foot hull at 7 knots at 400 rpm at 100 psi; it will operate as slowly as 20 rpm.  While it's cylinder walls are designed with a 10x hoop strength "safety" factor at 300 psi, this engine captures the pleasures of marine engineering at low pressure.

What do we mean by the term fitter?  Fitting was a trade that has nearly died out but that was essential in machine manufacturing before precision manufacturing, and was an essential task in producing engines.  Fitters took over after the machinists.  With trammels, gauges, and hand-scrapers they brought an assembly of machined parts into tolerance and alignment.  Imagine, for example, aligning a ten-foot-high cast column of a marine engine; the underside of its base had to be painstakingly scraped away to "tip" the column into position at its top.  Ten-thousandths off the base to move the top over by thousandths.  Even with boat-sized engines , more than machining is needed.  As Cliff Balckstaffe often reminded, "It was the fitters, not the machinists, that made rivalries for smoothness and quietness among the trans-Atlantic liners. "

To see an Elliott Bay Triple being built, go to Peter Cowie's Website at: .

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Cylinder Boring

Greg Linden of Sedalia, Colorado (former commander of a Navy tugboat with a triple expansion engine) supplied this photo of cylinder boring.  On the left, the cored passageways leading to the IP cylinder from the adjacent piston valve can be seen; the cutter has just finished first cut on the LP bore.  Note the relief cuts in the bores of the finished block which all "run-by" of the pistons to prevent moraine build up, a requirement for long life.

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