High-speed 4-stroke diesels (often ~1,800 rpm class) in smaller and mid-size harbor/utility tugs
Two-stroke Detroit diesels (71/92 series) across a wide range of older and mid-power tugs
Medium-speed, heavy-duty engines (often ~900 rpm class), especially EMD 645 and, in some higher-power cases, Cat’s emerging 3600 series
Below is the most common “short list,” organized by what you actually tend to find on 1980s-built tugs.
1) EMD 645 (medium-speed two-stroke) — extremely common in higher-horsepower towing tugs
If you’re looking at larger 1980s conventional towing tugs (coastal/ocean towing and heavy barge work), EMD 645is one of the most frequently encountered engine families. The 645 was explicitly produced for locomotive, marine, and stationary use, and marine versions commonly run up to about 900 rpm.
Real-world tug examples (1980s vintage)
A 1980 tug example is documented as having two EMD 645E-7 engines producing 7,200 HP total.
A 1979 sea-barge tug technical summary lists two EMD 16-645 engines at 900 rpm and 2,800 bhp each, which reflects the same propulsion pattern widely used into the 1980s.
Where you saw them most (1980–1990):
Larger conventional towing tugs
Heavy assist / towing units where durability at sustained power mattered
Fleets standardized around EMD maintenance capability
2) Detroit Diesel two-strokes — Series 71 and Series 92 (highly prevalent across older and mid-power tugs)
Detroit Diesel’s Series 71 and later Series 92 were widespread in marine service for decades, and they show up constantly in 1980s tug inventories.
Series 71 production ran 1938–1995, and the series is widely documented as popular in marine applications.
Series 92 was introduced in 1974 as a successor family to the 71 series and was broadly adopted across many heavy-duty applications.
Common tug-relevant configurations you’ll encounter:
71 Series: 6-71 / 8V-71 / 12V-71 / 16V-71 (depending on vessel size and refits)
92 Series: 6V92 / 8V92 / 12V92 / 16V92 (in higher-output two-stroke packages)
Where you saw them most (1980–1990):
Older harbor tugs still in service through the 80s
Utility/work tugs and mixed fleets
Some coastal towing tugs, particularly where Detroit parts/knowledge were entrenched
3) Cummins KT/KTA family — KTA19, KTA38, KTA50 (common high-speed 4-stroke workboat/tug engines)
Cummins’ KT/KTA line is a classic commercial marine workhorse set, and it was very commonly specified or found in 1980s tug/workboat builds and repowers.
Cummins continues to publish dedicated “for Marine” pages for:
KTA19 for Marine
KTA38 for Marine
KTA50 for Marine
There are also fleet examples of 1980s towboats/tugs documented with twin KTA19 installations (typical of that decade’s smaller-to-mid towboat power band).
Where you saw them most (1980–1990):
Harbor/utility tugs (KTA19 and KTA38 especially)
Inland and near-coastal towing units
Operators prioritizing straightforward service and broad support
4) Caterpillar 3406/3400 series (high-speed 4-stroke) — very common in smaller-to-mid tug/workboat power bands
In the 1980s, Caterpillar’s 3400-family engines were widely used in commercial marine propulsion for workboats and smaller tugs. A representative example that remained common in the late 1980s is the mechanically governed Cat 3406C marine propulsion engine, rated around 365–400 bhp at 1800 rpm.
Where you saw them most (1980–1990):
Smaller harbor/utility tugs
Work tugs and service craft
Fleets that valued mechanical simplicity and dealer support
5) Caterpillar 3600 series (medium-speed) — less “by count,” but important in higher-power commercial marine applications from mid-80s onward
If you’re looking at the upper end of 1980s commercial marine power, Cat’s 3600 series begins to appear meaningfully after it goes into production in the mid-1980s:
A Maritime Reporter piece (June 1986) states Cat’s 3600 series entered production at its Lafayette plant and notes North American field operations began in August 1984, including examples of 3606 and 3612 marine engines in service.
How this shows up in tugs (1980–1990):
More niche than EMD/Detroit/Cummins in tugboats by raw count
But relevant for higher-horsepower commercial operators and certain markets where Cat medium-speed solutions were adopted post-1984
Practical Cheat Sheet (1980–1990)
If you want the “most likely engines” when you inspect a tug built in the 1980s:
Smaller harbor/utility tug
Cat 3406-class commercial marine propulsion
Cummins KTA19/KTA38
Detroit Diesel 71 series in many legacy builds
Mid-power tug / mixed work
Cummins KTA38/KTA50
Detroit Diesel 92 series increasingly common alongside 71s
Higher-horsepower towing tug
EMD 645 (very common; 900 rpm class marine engines)
Some Cat 3600 series adoption from mid-80s onward in higher-power commercial marine contexts.
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