This is a factory fresh VT12-825-M image from the original sales literature that is still in the ship’s engineering files from the time the engine was purchased.  

1964 Cummins  VT12-825-M

Not all diesel engines have glamorous jobs in fancy places… like under the hood of your pickup. Some toil in the dark, buried deep in the bowels of a ship. Such was the life of this 12-cylinder Cummins VT12, also known as a VT12-825-M.

Here is where the Cummins V12 started, the 1936 Model VL. In the mid-1930s, the practicality of a diesel powered locomotive was starting to compete with the  steamers and developments were ongoing in diesel manufacturing to accommodate that market. Cummins got involved, first by building a locomotive powered by two 250 hp Model L sixes. Cummins engineers then put two of the 2309 cubic inch model Ls together on one crankcase in a 60 degree vee to make the 500 horsepower (at 1000 rpm) VL. A pair of these babies were installed into a locomotive for tests but the project didn’t get far. General Electric and General Motors soon became heavy hitters in diesel locomotive development and Cummins wisely realized they were outclassed and dropped their locomotive work. This VL is shown with the new Cummins Model A automotive engine about 1937. Only about 15 of these engines were produced.

In 1966 when the Great lakes ore boat SS Col. James M. Schoonmaker was 55 years old, she got a very useful upgrade in the form of a bow thruster. “What’s that?” you landlubbers ask. In the simplest terms, it’s propulsion that moves a ship sideways rather than forward or back. It’s very useful for maneuvering to or away from dock. It’s typically located in the forward part of a vessel but some have them in several locations.

VT12 engine number 391965 has lived it’s entire life on the bottom level of the bow section of SS Schoonmaker. Over 14 years of service, it acquired 3,445 hours of operation. It started via air supplied by a compressor elsewhere on the boat. Cooling comes from a cooling grid inside the propeller tunnel and the system holds 90 gallons.

A ship the size of Schoonmaker won’t get by with an outboard-sized bow thruster, so when the thruster was added in the ‘65-66 off-season, they needed some beef. The engine selected was the marineized VT12-825-M. The “825” indicated the 825 horsepower pleasure boat rating, the highest rating for this engine family at the time, the absolute maximum intermittent allowable output in marine use. In normal marine use, the operator would limit operation to 700 horsepower at 1850 rpm.

VT12 History

The conceptual origins of the V1710 Series go back to the mid-1930s and a monstrous 4,638 cubic inch V12 Cummins built for use in an experimental diesel locomotive. Cummins Engineer and Historian, Keith Baylor, says only about 15 of these engines were built.

The VT12 is more or less as it was when last run in 1980. Condition is unknown but after sitting 41 years in a dank hold, it’s likely to be locked up. We know a bunch of you are screaming, “Somebody go down there and get ‘er running.” That’s what all gearheads will think but the Museum of the Great Lakes has a lot of obstacles in the way of that. Besides insurance, repair costs and fabricating a new stack (the old one was cut off and capped many years back), there are maritime regulations that prevent the museum from running any of the engines without jumping thru a whole lot of very expensive hoops. Sadly, this diesel’s running days are over. Too bad hardly anyone ever goes down there to pat it on the cylinder head and say thanks.

Next up was the V1486 in the NVH line that debuted in March of 1949, originally with a Double Disc injection system. It displaced 1,486 cubic inches from a 5.125 x 6-inch bore and stroke. Baylor tells us that in 1953, the V1486 was the first production Cummins engine to be turbocharged. It was also the first to be converted to the PT injection system in January of 1954. The NA variants were typically called the NVH-12 (or NVH-1200) and the turbocharged units VT12. They typically cranked out a maximum rated 400 and 600 horses respectively, both at 2100 rpm. Production ran into 1968 and overlapped with the V1710 series. There were also 600 horsepower supercharged models.

The engine sets just aft of the thruster tunnel and drives an American Shipbuilding Company “AmThrust” dual counter-rotating propeller thruster unit. Between the engine and the AmThrust is a Twin Disc MG-521 gearbox with a 4.087:1 ratio. The AmThrust adds another 1.33:1 ratio drop.
The thruster tunnel on Schoonmaker is about 6.3 feet in diameter, just a few inches larger than the six foot diameter, counter-rotating AmThrust propellers. The AmThrust can produce 18,000 pounds of thrust using 700 of the VT12’s horsepower. That’s a little more thrust than one jet engine on a Boing 737 airliner can produce.

The V1710 series debuted for 1960 in two forms, naturally aspirated and turbocharged. In development, the NA engine was internally code-named “Volume” and the turbo was “Victor.” They were introduced at the same time as the venerated 855 cubic inch NH six and a little known and short lived (‘60-67) 950 cubic inch V8 called the VT8 or V950. A natural gas fuel V1710 was introduced at the same time. They can generally be considered to all be in the same family.

The Captain had full control of the bow thruster from the bridge via this control and could monitor operation via the panel. Tom Kubiak, the ship’s maintenance supervisor, describes the addition of the bow thruster as a major milestone in the boat’s life, allowing the owners to save a great deal of money on tugboat fees. Remember that the ship’s main propulsion is at one end only and its ability to move the ship, or the ships bow, laterally is very limited. The Schoonmaker is 617 feet long and was once the largest ship on the Great Lakes. In her later years, she was still in the “big’un” class of lake boats. Even with tugs assisting, as they almost always did before the thruster was installed, tying up a vessel displacing 32,600 tons (that’s with a full load) was an epic event. The bow thruster enabled the Captain to push or hold the ships bow against wind or tide, or move the bow towards or away from a dock or pier. The bow thruster would also be very useful in the Soo Locks that connect Lakes Superior and Huron or in navigating in tight river spaces or harbors. The thruster paid for itself quickly by significantly cutting operating costs and reducing delays.

The V1710 series was designed for heavy construction, industrial, generators and marine use. It was a little big for trucks, though the VT8 did find a home in trucks. In the 1964 era of Schoonmaker’s unit, the V1710 NA versions typically had a base maximum power rating of 525 horsepower at 2100 rpm and the VT line was 700. In 1968, the VT1710 line was aftercooled and the ratings bumped to 800 and later 900 horsepower. A 980 horsepower rating is the highest shown for the latest engines in the books we have. The V1710 series has survived into today as the V28 or VTA28. It’s built overseas (India and China) and used overseas as a non-emissions engine in marine, construction and generator applications. Cummins considers it one of their home runs.

VT12 Tech

The VT12 is a V-12 with a narrow 40 degree vee. You could say the VT12 is two 855 sixes put together onto one crankshaft. It displaces 1,710 cubic inches from 12 cylinders with a 5.5 x 6.0 inch bore and stroke. It uses the Cummins PT injection system, which was an early iteration of a common rail system that is still being used by Cummins, both in it’s original or a modified form depending on the market. It has seven main bearings, the journals of which are 5-inches in diameter. The rod journals are 3.75 inches in diameter. Wet sleeves are used and the aluminum pistons have three compression and one oil ring. The piston pin is full floating, with hearings in the piston and the rod. Compression ratio is 14.1:1. The VT12-825-M assembly, complete with gearbox, weighs 8,100 pounds.

The predecessor and short time stablemate the V1710 series was the V1486 line. Here is a 1952 NVHIS-1486 at the Cummins Historical Restoration facility being evaluated by Engineers Ben Schulte to see if it’s in good enough shape to run again. The engine powered a backup generator in a large Rhode Island building. This supercharged version makes over 600 horsepower using two Cummins Twin Disc injection pumps. Four of the turbocharged versions of these engines were used to power the 95-foot Coast Guard Cape-Class Cutters starting the early 1950s.
This is a factory fresh VT12-825-M image from the original sales literature that is still in the ship’s engineering files from the time the engine was purchased.

At full intermittent power, the performance graph shows the engine would use approximately 47 gallons per hour. Baylor supplied the build card for the Schoonmaker engine and it was certified March 25, 1964. In its test, the engine delivered 16 psi boost, about what you’d expect for an engine with no intercooler, and used 43 gallons per hour at an 800 horsepower rating. The VT12 engine saw a lot of use here in the states until emissions controls hit the heavy duty diesel market.

Locked Away For Life

The Schoonmaker’s thruster engine compartment is six decks down from the bridge, literally as low as you can go in the boat. Because the path to it is a narrow, dark, steep and torturous, it isn’t on the museum tour route. It’s not likely the old Cummins will ever be seen by more than a few people. It’s not likely to run again either. In a way, it’s kind of sad that something once so useful to the operation of this ship, something that kept an old ship working efficiently in the modern era, has to retire in total obscurity. Perhaps this story will inspire a few of you old soot heads to raise a glass to a bit of mechanical history that was once a very important part of a very historic ship.



Museum of the Great Lakes


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