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.
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.
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.
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.
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 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 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.
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.
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